Sample records for fabricate quantum dots

  1. Design and fabrication of quantum-dot lasers

    E-Print Network [OSTI]

    Nabanja, Sheila

    2008-01-01T23:59:59.000Z

    Semiconductor lasers using quantum-dots in their active regions have been reported to exhibit significant performance advantages over their bulk semiconductor and quantum-well counterparts namely: low threshold current, ...

  2. SiGe quantum dot single-hole transistor fabricated by atomic force microscope nanolithography and silicon epitaxial-regrowth

    E-Print Network [OSTI]

    Rokhinson, Leonid

    SiGe quantum dot single-hole transistor fabricated by atomic force microscope nanolithography; published online 10 November 2006 A SiGe quantum dot single-hole transistor passivated by silicon epitaxial are reproducible, in sharp contrast with the noisy and irreproducible I-V characteristics of unpassivated SiGe

  3. Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

    E-Print Network [OSTI]

    Payette, C; Koppinen, P J; Dovzhenko, Y; Sturm, J C; Petta, J R

    2011-01-01T23:59:59.000Z

    We perform quantum Hall measurements on three types of commercially available modulation doped Si/SiGe heterostructures to determine their suitability for depletion gate defined quantum dot devices. By adjusting the growth parameters, we are able to achieve electron gases with charge densities 1-3 X 10^{11}/cm^2 and mobilities in excess of 100,000 cm^2/Vs. Double quantum dot devices fabricated on these heterostructures show clear evidence of single charge transitions as measured in dc transport and charge sensing and exhibit electron temperatures of 100 mK in the single quantum dot regime.

  4. Single charge sensing and transport in double quantum dots fabricated from commercially grown Si/SiGe heterostructures

    E-Print Network [OSTI]

    C. Payette; K. Wang; P. J. Koppinen; Y. Dovzhenko; J. C. Sturm; J. R. Petta

    2012-03-21T23:59:59.000Z

    We perform quantum Hall measurements on three types of commercially available modulation doped Si/SiGe heterostructures to determine their suitability for depletion gate defined quantum dot devices. By adjusting the growth parameters, we are able to achieve electron gases with charge densities 1-3 X 10^{11}/cm^2 and mobilities in excess of 100,000 cm^2/Vs. Double quantum dot devices fabricated on these heterostructures show clear evidence of single charge transitions as measured in dc transport and charge sensing and exhibit electron temperatures of 100 mK in the single quantum dot regime.

  5. Fabrication and optimization of light emitting devices with core-shell quantum dots

    E-Print Network [OSTI]

    Song, Katherine Wei

    2013-01-01T23:59:59.000Z

    Quantum dot light emitting devices (QD-LEDs) are promising options for the next generation of solid state lighting, color displays, and other optoelectronic applications. Overcoating quantum dots (QDs) -- semiconducting ...

  6. Fabrication and characterization of p-channel Si double quantum dots

    SciTech Connect (OSTI)

    Yamada, Ko; Kambara, Tomohiro; Oda, Shunri [Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552 (Japan); Kodera, Tetsuo, E-mail: kodera.t.ac@m.titech.ac.jp [Department of Physical Electronics, Quantum Nanoelectronics Research Center, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552 (Japan); PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho Kawaguchi, Saitama 332-0012 (Japan)

    2014-09-15T23:59:59.000Z

    Lithographically defined p-channel Si single hole transistors (SHTs) and double quantum dot (DQD) devices are fabricated and characterized. Coulomb oscillations are clearly evident at a temperature of 4.2?K. The charging energy and the diameter of the SHT are estimated from the Coulomb diamonds. Honeycomb-like charge stability diagrams are observed from measurements of the DQD devices. Single hole transitions through the DQD are detected using an integrated SHT as a charge sensor, and a few-hole regime of the DQD is observed.

  7. Quantum dot Ge/TiO{sub 2} heterojunction photoconductor fabrication and performance

    SciTech Connect (OSTI)

    Church, Carena P.; Carter, Sue A., E-mail: sacarter@ucsc.edu [Department of Physics, University of California Santa Cruz, Santa Cruz, California 95064 (United States); Muthuswamy, Elayaraja; Kauzlarich, Susan M. [Department of Chemistry, University of California Davis, Davis, California 95616 (United States)] [Department of Chemistry, University of California Davis, Davis, California 95616 (United States); Zhai, Guangmei [Key Laboratory of Interface Science and Engineering in Advanced Materials of Ministry of Education, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030024 (China)] [Key Laboratory of Interface Science and Engineering in Advanced Materials of Ministry of Education, Taiyuan University of Science and Technology, Taiyuan, Shanxi 030024 (China)

    2013-11-25T23:59:59.000Z

    Spun cast TiO{sub 2}-Ge quantum dot (QD) heterojunction type photodetectors have been fabricated and characterized, with interest paid to photocurrent enhancements related to device design. Performance as a function of absorber layer thickness, QD size, and back contact is investigated. We have achieved ultra-thin (?200?nm) devices with photocurrents at 0.5?V of 10{sup ?4} A cm{sup ?2} while the thickest devices have photocurrents at 0.5?V of 10{sup ?2} A cm{sup ?2} with on-off ratios >100, which represents 5 orders of magnitude increase in photocurrents over previously fabricated Ge QD devices. At 0.5?V bias, the currents in our devices are competitive with thin-film Ge photovoltaics.

  8. Fabrication of InAs quantum dots in AlAs/GaAs DBR pillar microcavities for single photon sources

    SciTech Connect (OSTI)

    Zhang Bingyang; Solomon, Glenn S.; Pelton, Matthew; Plant, Jocelyn; Santori, Charles; Vuckovic, Jelena; Yamamoto, Yoshihisa [Quantum Entanglement Project, ICORP, JST, Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085 (United States)

    2005-04-01T23:59:59.000Z

    We report the molecular beam epitaxy growth of low-density strain-induced InAs quantum dots (QD) embedded in an AlAs/GaAs distributed Bragg reflector structure for a triggered photon source. By optimal selection of growth temperature, InAs deposited thickness and other experimental parameters, it is possible to grow low density (10/{mu}m{sup 2}) InAs quantum dots with a suitable emission wavelength for a triggered photon source. The empirical formulas for the refractive indices of AlAs and GaAs materials at high temperature over a wide wavelength range are constructed by combining high resolution x-ray diffraction, dynamic optical reflectivity, and optical reflectivity spectrum techniques. Utilizing the electron-beam lithography and electron-cyclotron-resonance plasma etching techniques, a micropost microcavity with the top diameter of 0.6 {mu}m and the post height of 4.2 {mu}m has been fabricated. Narrow, spectrally limited single QD emission embedded in a micropost microcavity is observed in the photoluminescence.

  9. Semiconductor quantum dots with light-hole exciton ground state: fabrication and fine structure

    E-Print Network [OSTI]

    Y. H. Huo; B. J. Witek; S. Kumar; R. Singh; E. Zallo; R. Grifone; D. Kriegner; R. Trotta; N. Akopian; J. Stangl; V. Zwiller; G. Bester; A. Rastelli; O. G. Schmidt

    2012-08-31T23:59:59.000Z

    Quantum dots (QDs) can act as convenient hosts of two-level quantum szstems, such as single electron spins, hole spins or excitons (bound electron-hole pairs). Due to quantum confinement, the ground state of a single hole confined in a QD usually has dominant heavy-hole (HH) character. For this reason light-hole (LH) states have been largely neglected, despite the fact that may enable the realilzation of coherent photon-to-spin converters or allow for faster spin manipulation compared to HH states. In this work, we use tensile strains larger than 0.3% to switch the ground state of excitons confined in high quality GaAs/AlGaAs QDs from the conventional HH- to LH-type. The LH-exciton fine structure is characterized by two in-plane-polarized lines and, ~400 micro-eV above them, by an additional line with pronounced out-of-plane oscillator strength, consistent with theoretical predictions based on atomistic empirical pseudopotential calculations and a simple mesoscopic model.

  10. Quantum Dots: Theory

    E-Print Network [OSTI]

    Vukmirovic, Nenad

    2010-01-01T23:59:59.000Z

    Petersilka, Density Functional Theory (Springer, New York,Quantum Dots: Theory Nenad Vukmirovi´ and Lin-Wang Wang cdensity functional theory; electronic structure; empirical

  11. Dynamics of Quantum Dot Photonic Crystal Lasers

    E-Print Network [OSTI]

    Bryan Ellis; Ilya Fushman; Dirk Englund; Bingyang Zhang; Yoshihisa Yamamoto; Jelena Vuckovic

    2007-03-07T23:59:59.000Z

    Quantum dot photonic crystal membrane lasers were fabricated and the large signal modulation characteristics were studied. We find that the modulation characteristics of quantum dot lasers can be significantly improved using cavities with large spontaneous emission coupling factor. Our experiments show, and simulations confirm, that the modulation rate is limited by the rate of carrier capture into the dots to around 30GHz in our present system.

  12. A quantum dot heterojunction photodetector

    E-Print Network [OSTI]

    Arango, Alexi Cosmos, 1975-

    2005-01-01T23:59:59.000Z

    This thesis presents a new device architecture for photodetectors utilizing colloidally grown quantum dots as the principle photo-active component. We implement a thin film of cadmium selenide (CdSe) quantum dot sensitizers, ...

  13. Synthesis of CdSe quantum dots for quantum dot sensitized solar cell

    SciTech Connect (OSTI)

    Singh, Neetu, E-mail: singh.neetu1985@gmail.com; Kapoor, Avinashi [Department of Electronic Science, University of Delhi South Campus, New Delhi-110 021 (India); Kumar, Vinod [Department of Physics, University of the Free State, Bloemfontein, ZA9300 (South Africa); Mehra, R. M. [School of Engineering and Technology, Sharda University, Greater Noida-201 306, U.P. (India)

    2014-04-24T23:59:59.000Z

    CdSe Quantum Dots (QDs) of size 0.85 nm were synthesized using chemical route. ZnO based Quantum Dot Sensitized Solar Cell (QDSSC) was fabricated using CdSe QDs as sensitizer. The Pre-synthesized QDs were found to be successfully adsorbed on front ZnO electrode and had potential to replace organic dyes in Dye Sensitized Solar Cells (DSSCs). The efficiency of QDSSC was obtained to be 2.06 % at AM 1.5.

  14. Nontoxic quantum dot research improves solar cells

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Nontoxic quantum dot research improves solar cells Nontoxic quantum dot research improves solar cells Solar cells made with low-cost, nontoxic copper-based quantum dots can achieve...

  15. The effects of fabrication temperature on current-voltage characteristics and energy efficiencies of quantum dot sensitized ZnOH-GO hybrid solar cells

    SciTech Connect (OSTI)

    Islam, S. M. Z. [IUSL, Department of Physics, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Department of Physics and Engineering Physics, Fordham University, 441 E. Fordham Road, Bronx, New York 10458 (United States); Department of Electrical Engineering, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Gayen, Taposh [IUSL, Department of Physics, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Department of Physics and Engineering Physics, Fordham University, 441 E. Fordham Road, Bronx, New York 10458 (United States); Tint, Naing; Alfano, Robert, E-mail: ralfano@sci.ccny.cuny.edu [IUSL, Department of Physics, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Department of Electrical Engineering, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Shi, Lingyan [IUSL, Department of Physics, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Department of Biomedical Engineering, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States); Seredych, Mykola; Bandosz, Teresa J. [Department of Chemistry, The City College of New York, 160 Convent Ave., New York, New York 10031 (United States)

    2014-11-07T23:59:59.000Z

    The effects of fabrication temperature are investigated on the performance of CdSe quantum dot (QD)-sensitized hybrid solar cells of the composite material of zinc (hydr)oxide (ZnOH-GO)with 2?wt.?% graphite oxide. The current-voltage (I-V) and photo-current measurements show that higher fabrication temperatures yield greater photovoltaic power conversion efficiencies that essentially indicate more efficient solar cells. Two Photon Fluorescence images show the effects of temperature on the internal morphologies of the solar devices based on such materials. The CdSe-QD sensitized ZnOH-GO hybrid solar cells fabricated at 450?°C showing conversion of ?10.60% under a tungsten lamp (12.1 mW/cm{sup 2}) are reported here, while using potassium iodide as an electrolyte. The output photocurrent, I (?A) with input power, P (mW/cm{sup 2}) is found to be superlinear, showing a relation of I?=?P{sup n}, where n?=?1.4.

  16. Self-organized formation of quantum dots of a material on a substrate

    DOE Patents [OSTI]

    Zhang, Zhenyu (232 Long Bow Rd., Knoxville, TN 37922); Wendelken, John F. (925 Suwanee Rd., Knoxville, TN 37923); Chang, Ming-Che (F4-2, No. 178 Sec 5 Minsheng East Rd., Taipei, TW); Pai, Woei Wu (1F, No. 17, Alley 11, Lane 202, Ming Chyuan Rd., Pan Chou City, Taipei County, TW)

    2001-01-01T23:59:59.000Z

    Systems and methods are described for fabricating arrays of quantum dots. A method for making a quantum dot device, includes: forming clusters of atoms on a substrate; and charging the clusters of atoms such that the clusters of atoms repel one another. The systems and methods provide advantages because the quantum dots can be ordered with regard to spacing and/or size.

  17. Nanoscale engineering boosts performance of quantum dot light...

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum dot light emitting diodes Nanoscale engineering boosts performance of quantum dot light emitting diodes Quantum dots are nano-sized semiconductor particles whose emission...

  18. Quantum dot conjugates in a sub-micrometer fluidic channel

    DOE Patents [OSTI]

    Stavis, Samuel M.; Edel, Joshua B.; Samiee, Kevan T.; Craighead, Harold G.

    2010-04-13T23:59:59.000Z

    A nanofluidic channel fabricated in fused silica with an approximately 500 nm square cross section was used to isolate, detect and identify individual quantum dot conjugates. The channel enables the rapid detection of every fluorescent entity in solution. A laser of selected wavelength was used to excite multiple species of quantum dots and organic molecules, and the emission spectra were resolved without significant signal rejection. Quantum dots were then conjugated with organic molecules and detected to demonstrate efficient multicolor detection. PCH was used to analyze coincident detection and to characterize the degree of binding. The use of a small fluidic channel to detect quantum dots as fluorescent labels was shown to be an efficient technique for multiplexed single molecule studies. Detection of single molecule binding events has a variety of applications including high throughput immunoassays.

  19. INSTITUTE for QUANTUM STRUCTURES AND DEVICES

    E-Print Network [OSTI]

    Plotkin, Steven S.

    , and #12;the design and fabrication of quantum devices based on magnetic, quantum dot, and superconducting

  20. Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors

    SciTech Connect (OSTI)

    Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A. [Department of Engineering Mathematics and Physics, Faculty of Engineering, Cairo University, Giza (Egypt)

    2014-02-14T23:59:59.000Z

    A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.

  1. Quantum Dot Light Emitting Diode

    SciTech Connect (OSTI)

    Kahen, Keith

    2008-07-31T23:59:59.000Z

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m{sup 2}, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  2. Quantum Dot Light Emitting Diode

    SciTech Connect (OSTI)

    Keith Kahen

    2008-07-31T23:59:59.000Z

    The project objective is to create low cost coatable inorganic light emitting diodes, composed of quantum dot emitters and inorganic nanoparticles, which have the potential for efficiencies equivalent to that of LEDs and OLEDs and lifetime, brightness, and environmental stability between that of LEDs and OLEDs. At the end of the project the Recipient shall gain an understanding of the device physics and properties of Quantum-Dot LEDs (QD-LEDs), have reliable and accurate nanocrystal synthesis routines, and have formed green-yellow emitting QD-LEDs with a device efficiency greater than 3 lumens/W, a brightness greater than 400 cd/m2, and a device operational lifetime of more than 1000 hours. Thus the aim of the project is to break the current cost-efficiency paradigm by creating novel low cost inorganic LEDs composed of inorganic nanoparticles.

  3. Temperature-Dependent Electron Transport in Quantum Dot Photovoltaics

    E-Print Network [OSTI]

    Padilla, Derek

    2013-01-01T23:59:59.000Z

    4.4 Photovoltaics in Practice . . . . . . . . . . . . . .milestones. Quantum dot photovoltaics is in the bottom-rightIN QUANTUM DOT PHOTOVOLTAICS A dissertation submitted in

  4. Temperature-Dependent Electron Transport in Quantum Dot Photovoltaics

    E-Print Network [OSTI]

    Padilla, Derek

    2013-01-01T23:59:59.000Z

    cell efficiency milestones. Quantum dot photovoltaics is inphotovoltaics provide the potential to create high-efficiencycell efficiency milestones. Quantum dot photovoltaics is in

  5. A Graphene Quantum Dot with a Single Electron Transistor as Integrated Charge Sensor

    E-Print Network [OSTI]

    Ling-Jun Wang; Gang Cao; Tao Tu; Hai-Ou Li; Cheng Zhou; Xiao-Jie Hao; Zhan Su; Guang-Can Guo; Guo-Ping Guo; Hong-Wen Jiang

    2010-08-28T23:59:59.000Z

    We have developed an etching process to fabricate a quantum dot and a nearby single electron transistor as a charge detector in a single layer graphene. The high charge sensitivity of the detector is used to probe Coulomb diamonds as well as excited spectrum in the dot, even in the regime where the current through the quantum dot is too small to be measured by conventional transport means. The graphene based quantum dot and integrated charge sensor serve as an essential building block to form a solid-state qubit in a nuclear-spin-free quantum world.

  6. Development of low-temperature solution-processed colloidal quantum dot-based solar cells

    E-Print Network [OSTI]

    Chang, Liang-Yi, Ph. D. Massachusetts Institute of Technology

    2013-01-01T23:59:59.000Z

    Solution-processed solar cells incorporating organic semiconductors and inorganic colloidal quantum dots (QDs) are potential alternatives to conventional solar cells fabricated via vacuum or high-temperature sintering ...

  7. Thick-shell nanocrystal quantum dots

    DOE Patents [OSTI]

    Hollingsworth, Jennifer A. (Los Alamos, NM); Chen, Yongfen (Eugene, OR); Klimov, Victor I. (Los Alamos, NM); Htoon, Han (Los Alamos, NM); Vela, Javier (Los Alamos, NM)

    2011-05-03T23:59:59.000Z

    Colloidal nanocrystal quantum dots comprising an inner core having an average diameter of at least 1.5 nm and an outer shell, where said outer shell comprises multiple monolayers, wherein at least 30% of the quantum dots have an on-time fraction of 0.80 or greater under continuous excitation conditions for a period of time of at least 10 minutes.

  8. Phonon Mediated Off-Resonant Quantum Dot-Cavity Coupling

    E-Print Network [OSTI]

    Arka Majumdar; Yiyang Gong; Erik D. Kim; Jelena Vuckovic

    2010-12-14T23:59:59.000Z

    A theoretical model for the phonon-mediated off-resonant coupling between a quantum dot and a cavity, under resonant excitation of the quantum dot, is presented. We show that the coupling is caused by electron-phonon interaction in the quantum dot and is enhanced by the cavity. We analyze recently observed resonant quantum dot spectroscopic data by our theoretical model.

  9. Semiconductor Quantum Dots and Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells

    E-Print Network [OSTI]

    George, Steven C.

    to Third-Generation Photovoltaic Solar Cells A. J. Nozik,*,, M. C. Beard, J. M. Luther, M. Law,§ R. J. Applications: Quantum Dot Solar Cells 6884 6.1. Quantum Dot Solar Cell Configurations 6885 6.1.1. Photoelectrodes Composed of Quantum Dot Arrays 6885 6.1.2. Quantum Dot-Sensitized Nanocrystalline TiO2 Solar Cells

  10. Photodetectors based on colloidal quantum dots

    E-Print Network [OSTI]

    Oertel, David C. (David Charles)

    2007-01-01T23:59:59.000Z

    Inspired by recent work demonstrating photocurrent enhancement in quantum-dot (QD) solids via post-deposition chemical annealing and by recent successes incorporating single monolayers of QDs in light-emitting devices ...

  11. Synthesis and characterization of infrared quantum dots

    E-Print Network [OSTI]

    Harris, Daniel Kelly

    2014-01-01T23:59:59.000Z

    This thesis focuses on the development of synthetic methods to create application ready quantum dots (QDs) in the infrared for biological imaging and optoelectronic devices. I concentrated primarily on controlling the size ...

  12. Single photon emission from site-controlled InGaN/GaN quantum dots

    SciTech Connect (OSTI)

    Zhang, Lei; Hill, Tyler A.; Deng, Hui, E-mail: dengh@umich.edu [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109 (United States)] [Department of Physics, University of Michigan, 450 Church Street, Ann Arbor, Michigan 48109 (United States); Teng, Chu-Hsiang; Lee, Leung-Kway; Ku, Pei-Cheng, E-mail: peicheng@umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)] [Department of Electrical Engineering and Computer Science, University of Michigan, 1301 Beal Ave., Ann Arbor, Michigan 48109 (United States)

    2013-11-04T23:59:59.000Z

    Single photon emission was observed from site-controlled InGaN/GaN quantum dots. The single-photon nature of the emission was verified by the second-order correlation function up to 90?K, the highest temperature to date for site-controlled quantum dots. Micro-photoluminescence study on individual quantum dots showed linearly polarized single exciton emission with a lifetime of a few nanoseconds. The dimensions of these quantum dots were well controlled to the precision of state-of-the-art fabrication technologies, as reflected in the uniformity of their optical properties. The yield of optically active quantum dots was greater than 90%, among which 13%–25% exhibited single photon emission at 10?K.

  13. Thermoelectric transport through strongly correlated quantum dots

    E-Print Network [OSTI]

    T. A. Costi; V. Zlatic

    2010-07-08T23:59:59.000Z

    The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}< T_{2}$. Such sign changes in $S(T)$ are particularly sensitive signatures of strong correlations and Kondo physics. The relevance of this to recent thermopower measurements of Kondo correlated quantum dots is discussed. We discuss the figure of merit, power factor and the degree of violation of the Wiedemann-Franz law in quantum dots. The extent of temperature scaling in the thermopower and thermal conductance of quantum dots in the Kondo regime is also assessed.

  14. Engineered Quantum Dot Single Photon Sources

    E-Print Network [OSTI]

    Sonia Buckley; Kelley Rivoire; Jelena Vuckovic

    2012-10-03T23:59:59.000Z

    Fast, high efficiency, and low error single photon sources are required for implementation of a number of quantum information processing applications. The fastest triggered single photon sources to date have been demonstrated using epitaxially grown semiconductor quantum dots (QDs), which can be conveniently integrated with optical microcavities. Recent advances in QD technology, including demonstrations of high temperature and telecommunications wavelength single photon emission, have made QD single photon sources more practical. Here we discuss the applications of single photon sources and their various requirements, before reviewing the progress made on a quantum dot platform in meeting these requirements.

  15. Nanostructured architectures for colloidal quantum dot solar cells

    E-Print Network [OSTI]

    Jean, Joel, S.M. Massachusetts Institute of Technology

    2013-01-01T23:59:59.000Z

    This thesis introduces a novel ordered bulk heterojunction architecture for colloidal quantum dot (QD) solar cells. Quantum dots are solution-processed nanocrystals whose tunable bandgap energies make them a promising ...

  16. Electron tunneling and spin relaxation in a lateral quantum dot

    E-Print Network [OSTI]

    Amasha, Sami

    2008-01-01T23:59:59.000Z

    We report measurements that use real-time charge sensing to probe a single-electron lateral quantum dot. The charge sensor is a quantum point contact (QPC) adjacent to the dot and the sensitivity is comparable to other ...

  17. Fast quantum dot single photon source triggered at telecommunications wavelength

    E-Print Network [OSTI]

    Kelley Rivoire; Sonia Buckley; Arka Majumdar; Hyochul Kim; Pierre Petroff; Jelena Vuckovic

    2010-12-20T23:59:59.000Z

    We demonstrate a quantum dot single photon source at 900 nm triggered at 300 MHz by a continuous wave telecommunications wavelength laser followed by an electro-optic modulator. The quantum dot is excited by on-chip-generated second harmonic radiation, resonantly enhanced by a GaAs photonic crystal cavity surrounding the InAs quantum dot. Our result suggests a path toward the realization of telecommunications-wavelength-compatible quantum dot single photon sources with speeds exceeding 1 GHz.

  18. Mini Review Water-soluble quantum dots for biomedical applications

    E-Print Network [OSTI]

    ­emission matrix (EEM) reveals that quantum dots always emit the same lights no matter what excita- tion wavelength

  19. Postdoctoral Positions: Si/SiGe Quantum Dots and Quantum Computing Eriksson Group

    E-Print Network [OSTI]

    Saffman, Mark

    Postdoctoral Positions: Si/SiGe Quantum Dots and Quantum Computing Eriksson Group Department in the area of Si/SiGe quantum dots and quantum computing. Recent advances in our group include single

  20. Photoluminescence from In0.5Ga0.5As/GaP quantum dots coupled to photonic crystal cavities

    E-Print Network [OSTI]

    Kelley Rivoire; Sonia Buckley; Yuncheng Song; Minjoo Larry Lee; Jelena Vuckovic

    2012-01-05T23:59:59.000Z

    We demonstrate room temperature visible wavelength photoluminescence from In0.5Ga0.5As quantum dots embedded in a GaP membrane. Time-resolved above band photoluminescence measurements of quantum dot emission show a biexpontential decay with lifetimes of ~200 ps. We fabricate photonic crystal cavities which provide enhanced outcoupling of quantum dot emission, allowing the observation of narrow lines indicative of single quantum dot emission. This materials system is compatible with monolithic integration on Si, and is promising for high efficiency detection of single quantum dot emission as well as optoelectronic devices emitting at visible wavelengths.

  1. Single-dot optical emission from ultralow density well-isolated InP quantum dots

    SciTech Connect (OSTI)

    Ugur, A.; Hatami, F.; Masselink, W. T. [Department of Physics, Humboldt-Universitaet zu Berlin, Newtonstrasse 15, D-12489 Berlin (Germany); Vamivakas, A. N.; Lombez, L.; Atatuere, M. [Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE (United Kingdom)

    2008-10-06T23:59:59.000Z

    We demonstrate a straightforward way to obtain single well-isolated quantum dots emitting in the visible part of the spectrum and characterize the optical emission from single quantum dots using this method. Self-assembled InP quantum dots are grown using gas-source molecular-beam epitaxy over a wide range of InP deposition rates, using an ultralow growth rate of about 0.01 atomic monolayers/s, a quantum-dot density of 1 dot/{mu}m{sup 2} is realized. The resulting isolated InP quantum dots embedded in an InGaP matrix are individually characterized without the need for lithographical patterning and masks on the substrate. Such low-density quantum dots show excitonic emission at around 670 nm with a linewidth limited by instrument resolution. This system is applicable as a single-photon source for applications such as quantum cryptography.

  2. Scalable quantum computer architecture with coupled donor-quantum dot qubits

    DOE Patents [OSTI]

    Schenkel, Thomas; Lo, Cheuk Chi; Weis, Christoph; Lyon, Stephen; Tyryshkin, Alexei; Bokor, Jeffrey

    2014-08-26T23:59:59.000Z

    A quantum bit computing architecture includes a plurality of single spin memory donor atoms embedded in a semiconductor layer, a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, wherein a first voltage applied across at least one pair of the aligned quantum dot and donor atom controls a donor-quantum dot coupling. A method of performing quantum computing in a scalable architecture quantum computing apparatus includes arranging a pattern of single spin memory donor atoms in a semiconductor layer, forming a plurality of quantum dots arranged with the semiconductor layer and aligned with the donor atoms, applying a first voltage across at least one aligned pair of a quantum dot and donor atom to control a donor-quantum dot coupling, and applying a second voltage between one or more quantum dots to control a Heisenberg exchange J coupling between quantum dots and to cause transport of a single spin polarized electron between quantum dots.

  3. Bilayer graphene quantum dot defined by topgates

    SciTech Connect (OSTI)

    Müller, André; Kaestner, Bernd; Hohls, Frank; Weimann, Thomas; Pierz, Klaus; Schumacher, Hans W., E-mail: hans.w.schumacher@ptb.de [Physikalisch-Technische Bundesanstalt, Bundesallee 100, 38116 Braunschweig (Germany)

    2014-06-21T23:59:59.000Z

    We investigate the application of nanoscale topgates on exfoliated bilayer graphene to define quantum dot devices. At temperatures below 500 mK, the conductance underneath the grounded gates is suppressed, which we attribute to nearest neighbour hopping and strain-induced piezoelectric fields. The gate-layout can thus be used to define resistive regions by tuning into the corresponding temperature range. We use this method to define a quantum dot structure in bilayer graphene showing Coulomb blockade oscillations consistent with the gate layout.

  4. Gates controlled parallel-coupled double quantum dot on both single layer and bilayer graphene

    E-Print Network [OSTI]

    Lin-Jun Wang; Guo-Ping Guo; Da Wei; Gang Cao; Tao Tu; Ming Xiao; Guang-Can Guo; A. M. Chang

    2011-04-22T23:59:59.000Z

    Here we report the fabrication and quantum transport measurements of gates controlled parallel-coupled double quantum dot on both bilayer and single layer graphene. It is shown that the interdot coupling strength of the parallel double dots can be effectively tuned from weak to strong regime by both the in-plane plunger gates and back gate. All the relevant energy scales and parameters of the graphene parallel-coupled double dot can be extracted from the honeycomb charge stability diagrams revealed through the transport measurements.

  5. Thermoelectric transport through strongly correlated quantum dots

    E-Print Network [OSTI]

    Costi, T A; 10.1103/PhysRevB.81.235127

    2010-01-01T23:59:59.000Z

    The thermoelectric properties of strongly correlated quantum dots, described by a single level Anderson model coupled to conduction electron leads, is investigated using Wilson's numerical renormalization group method. We calculate the electronic contribution, $K_{\\rm e}$, to the thermal conductance, the thermopower, $S$, and the electrical conductance, $G$, of a quantum dot as a function of both temperature, $T$, and gate voltage, ${\\rm v}_g$, for strong, intermediate and weak Coulomb correlations, $U$, on the dot. For strong correlations and in the Kondo regime, we find that the thermopower exhibits two sign changes, at temperatures $T_{1}({\\rm v}_g)$ and $T_{2}({\\rm v}_g)$ with $T_{1}law in ...

  6. Quantum Dots Promise to Significantly Boost Solar Cell Efficiencies (Fact Sheet)

    SciTech Connect (OSTI)

    Not Available

    2013-08-01T23:59:59.000Z

    In the search for a third generation of solar-cell technologies, a leading candidate is the use of 'quantum dots' -- tiny spheres of semiconductor material measuring only about 2-10 billionths of a meter in diameter. Quantum dots have the potential to dramatically increase the efficiency of converting sunlight into energy -- perhaps even doubling it in some devices -- because of their ability to generate more than one bound electron-hole pair, or exciton, per incoming photon. NREL has produced quantum dots using colloidal suspensions; then, using molecular self-assembly, they have been fabricated into the first-ever quantum-dot solar cells. While these devices operate with only 4.4% efficiency, they demonstrate the capability for low-cost manufacturing.

  7. Local Quantum Dot Tuning on Photonic Crystal Chips

    E-Print Network [OSTI]

    Andrei Faraon; Dirk Englund; Ilya Fushman; Nick Stoltz; Pierre Petroff; Jelena Vuckovic

    2007-03-28T23:59:59.000Z

    Quantum networks based on InGaAs quantum dots embedded in photonic crystal devices rely on QDs being in resonance with each other and with the cavities they are embedded in. We developed a new technique based on temperature tuning to spectrally align different quantum dots located on the same chip. The technique allows for up to 1.8nm reversible on-chip quantum dot tuning.

  8. Quasiresonant Excitation of InP/InGaP Quantum Dots Using Second Harmonic Generated in a Photonic Crystal Cavity

    E-Print Network [OSTI]

    Buckley, Sonia; Hatami, Fariba; Vuckovic, Jelena

    2012-01-01T23:59:59.000Z

    Indistinguishable single photons are necessary for quantum information processing applications. Resonant or quasiresonant excitation of single quantum dots provides greater single photon indistinguishability than incoherent pumping, but is also more challenging experimentally. Here, we demonstrate high signal to noise quasiresonant excitation of InP/InGaP quantum dots. The excitation is provided via second harmonic generated from a telecommunications wavelength laser resonant with the fundamental mode of a photonic crystal cavity, fabricated at twice the quantum dot transition wavelength. The second harmonic is generated using the \\chi(2) nonlinearity of the InGaP material matrix.

  9. Quasiresonant Excitation of InP/InGaP Quantum Dots Using Second Harmonic Generated in a Photonic Crystal Cavity

    E-Print Network [OSTI]

    Sonia Buckley; Kelley Rivoire; Fariba Hatami; Jelena Vuckovic

    2012-10-03T23:59:59.000Z

    Indistinguishable single photons are necessary for quantum information processing applications. Resonant or quasiresonant excitation of single quantum dots provides greater single photon indistinguishability than incoherent pumping, but is also more challenging experimentally. Here, we demonstrate high signal to noise quasiresonant excitation of InP/InGaP quantum dots. The excitation is provided via second harmonic generated from a telecommunications wavelength laser resonant with the fundamental mode of a photonic crystal cavity, fabricated at twice the quantum dot transition wavelength. The second harmonic is generated using the \\chi(2) nonlinearity of the InGaP material matrix.

  10. Electron counting in quantum dots

    E-Print Network [OSTI]

    Fominov, Yakov

    source drain pg M. Sigrist Ciorga et al., PRB 61, R16315 (2000) Elzerman et al. PRB 67, 161308 (2003) #12 extreme near field optics #12;Photons or phonons? GaAs InAs Gustavsson et al., PRB 78, 035324 (2008) #12S. Schnez et al. PRB 78 (2008) 140 nm circular dot 1000-100-200 Energy (meV) 0 2 4 6 8 B(T) 0 100 200

  11. Deposition of colloidal quantum dots by microcontact printing for LED display technology

    E-Print Network [OSTI]

    Kim, LeeAnn

    2006-01-01T23:59:59.000Z

    This thesis demonstrates a new deposition method of colloidal quantum dots within a quantum dot organic light-emitting diode (QD-LED). A monolayer of quantum dots is microcontact printed as small as 20 ,Lm lines as well ...

  12. An environmental impact assessment of quantum dot photovoltaics (QDPV) from raw material acquisition through use

    E-Print Network [OSTI]

    Illinois at Chicago, University of

    An environmental impact assessment of quantum dot photovoltaics (QDPV) from raw material of Environmental Engineering, Beytepe, Ankara, Turkey b Institute for Environmental Science and Policy, University: Life cycle assessment Quantum dots Nanophotovoltaics Quantum dot photovoltaic modules Solar energy

  13. Separability and dynamical symmetry of Quantum Dots

    SciTech Connect (OSTI)

    Zhang, P.-M., E-mail: zhpm@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Zou, L.-P., E-mail: zoulp@impcas.ac.cn [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Horvathy, P.A., E-mail: horvathy@lmpt.univ-tours.fr [Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou (China); Laboratoire de Mathématiques et de Physique Théorique, Tours University (France); Gibbons, G.W., E-mail: G.W.Gibbons@damtp.cam.ac.uk [Department of Applied Mathematics and Theoretical Physics, Cambridge University, Cambridge (United Kingdom)

    2014-02-15T23:59:59.000Z

    The separability and Runge–Lenz-type dynamical symmetry of the internal dynamics of certain two-electron Quantum Dots, found by Simonovi? et al. (2003), are traced back to that of the perturbed Kepler problem. A large class of axially symmetric perturbing potentials which allow for separation in parabolic coordinates can easily be found. Apart from the 2:1 anisotropic harmonic trapping potential considered in Simonovi? and Nazmitdinov (2013), they include a constant electric field parallel to the magnetic field (Stark effect), the ring-shaped Hartmann potential, etc. The harmonic case is studied in detail. -- Highlights: • The separability of Quantum Dots is derived from that of the perturbed Kepler problem. • Harmonic perturbation with 2:1 anisotropy is separable in parabolic coordinates. • The system has a conserved Runge–Lenz type quantity.

  14. alloy quantum dots: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  15. assembled quantum dots: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  16. asymmetry quantum dots: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  17. Photovoltaic performance of ultra-small PbSe quantum dots

    E-Print Network [OSTI]

    Ma, Wanli

    2014-01-01T23:59:59.000Z

    Colloidal Quantum Dots for Photovoltaics: Fundamentals andSchottky-Quantum Dot Photovoltaics for Efficient InfraredDJ; Klimov, VI, Hybrid Photovoltaics Based on Semiconductor

  18. A quantum dot implementation of the quantum NAND algorithm

    E-Print Network [OSTI]

    J. M. Taylor

    2007-08-10T23:59:59.000Z

    We propose a physical implementation of the quantum NAND tree evaluation algorithm. Our approach, based on continuous time quantum walks, uses the wave interference of a single electron in a heirarchical set of tunnel coupled quantum dots. We find that the query complexity of the NAND tree evaluation does not suffer strongly from disorder and dephasing, nor is it directly limited by temperature or restricted dimensionality for 2-d structures. Finally, we suggest a potential application of this algorithm to the efficient determination of high-order correlation functions of complex quantum systems.

  19. Comment on "Analysis of quantum coherent semiconductor quantum dot p-i-n junction photovoltaic cells"

    E-Print Network [OSTI]

    Scully, Marlan O

    2010-01-01T23:59:59.000Z

    This is a comment on PRL paper by A.P. Kirk "Analysis of quantum coherent semiconductor quantum dot p-i-n junction photovoltaic cells"

  20. Controlling quantum dot energies using submonolayer bandstructure engineering

    SciTech Connect (OSTI)

    Yu, L.; Law, S.; Wasserman, D. [Department of Electrical and Computer Engineering, University of Illinois Urbana Champaign, Urbana, Illinois 61801 (United States); Jung, D.; Lee, M. L. [Department of Electrical Engineering, Yale University, New Haven, Connecticut 06520 (United States); Shen, J.; Cha, J. J. [Department of Mechanical Engineering and Materials Science and Energy Science Institute, Yale University, New Haven, Connecticut 06520 (United States)

    2014-08-25T23:59:59.000Z

    We demonstrate control of energy states in epitaxially-grown quantum dot structures formed by stacked submonolayer InAs depositions via engineering of the internal bandstructure of the dots. Transmission electron microscopy of the stacked sub-monolayer regions shows compositional inhomogeneity, indicative of the presence of quantum dots. The quantum dot ground state is manipulated not only by the number of deposited InAs layers, but also by control of the thickness and material composition of the spacing layers between submonolayer InAs depositions. In this manner, we demonstrate the ability to shift the quantum dot ground state energy at 77?K from 1.38?eV to 1.88?eV. The results presented offer a potential avenue towards enhanced control of dot energies for a variety of optoelectronic applications.

  1. Synthesis and optical properties of cadmium selenide quantum dots for white light-emitting diode application

    SciTech Connect (OSTI)

    Xu, Xianmei; Wang, Yilin; Gule, Teri; Luo, Qiang [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Zhou, Liya, E-mail: zhouliyatf@163.com [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China); Gong, Fuzhong [School of Chemistry and Chemical Engineering, Guangxi University, Nanning 53000 (China)

    2013-03-15T23:59:59.000Z

    Highlights: ? Stable CdSe QDs were synthesized by the one-step and two-level process respectively. ? The fabricated white LEDs show good white balance. ? CdSe QDs present well green to yellow band luminescence. ? CdSe QDs displayed a broad excitation band. - Abstract: Yellow light-emitting cadmium selenide quantum dots were synthesized using one-step and two-step methods in an aqueous medium. The structural luminescent properties of these quantum dots were investigated. The obtained cadmium selenide quantum dots displayed a broad excitation band suitable for blue or near-ultraviolet light-emitting diode applications. White light-emitting diodes were fabricated by coating the cadmium selenide samples onto a 460 nm-emitting indium gallium nitrite chip. Both samples exhibited good white balance. Under a 20 mA working current, the white light-emitting diode fabricated via the one-step and two-step methods showed Commission Internationale de l’Éclairage coordinates at (0.27, 0.23) and (0.27, 0.33), respectively, and a color rendering index equal to 41 and 37, respectively. The one-step approach was simpler, greener, and more effective than the two-step approach. The one-step approach can be enhanced by combining cadmium selenide quantum dots with proper phosphors.

  2. Single photoelectron spin detection and angular momentum transfer in a gate defined quantum dot

    E-Print Network [OSTI]

    Takafumi Fujita; Kazuhiro Morimoto; Haruki Kiyama; Giles Allison; Marcus Larsson; Arne Ludwig; Sascha R. Valentin; Andreas D. Wieck; Akira Oiwa; Seigo Tarucha

    2015-04-14T23:59:59.000Z

    Recent innovations in fabricating nanoscale confined spin systems have enabled investigation of fundamental quantum correlations between single quanta of photons and matter states. Realization of quantum state transfer from photon polarization to electron spin using gate defined quantum dots (QDs) may give evidence of preserved coherence of angular momentum basis states at the photon-spin interface. The interface would enlarge the concept of quantum information technology, in which single photogenerated electron spins are manipulated with the dots, but this remains a serious challenge. Here, we report the detection of single electron spins generated by polarized single photons via a double QD (DQD) to verify the angular momentum transfer from single photons to single electrons. Pauli spin blockade (PSB) is used to project the photoelectron spin state onto the up or down spin state. Our result promises the realization of coherent quantum state transfer and development of hybrid photon and spin quantum technology.

  3. Thin Film Solar Cells Derived from Sintered Semiconductor Quantum Dots: Cooperative Research and Development Final Report, CRADA number CRD-07-00226

    SciTech Connect (OSTI)

    Ginley, D. S.

    2010-07-01T23:59:59.000Z

    The NREL/Evident team will develop techniques to fabricate thin film solar cells where the absorption layers comprising the solar cells are derived from sintered semiconductor quantum dots.

  4. Manipulating Quantum Dots to Nanometer Precision by Control of Flow

    E-Print Network [OSTI]

    Waks, Edo

    Manipulating Quantum Dots to Nanometer Precision by Control of Flow Chad Ropp, Roland Probst on the dynamically manipulated QD. KEYWORDS Quantum dots, control, electroosmotic flow, subpixel averaging, photon of Standards and Technology, Gaithersburg, Maryland 20899 ABSTRACT We present a method for manipulating

  5. Quantum optics and cavity QED with quantum dots in photonic crystals

    E-Print Network [OSTI]

    Jelena Vuckovic

    2014-02-11T23:59:59.000Z

    This chapter will primarily focus on the studies of quantum optics with semiconductor, epitaxially grown quantum dots embedded in photonic crystal cavities. We will start by giving brief introductions into photonic crystals and quantum dots, then proceed with the introduction to cavity quantum electrodynamics (QED) effects, with a particular emphasis on the demonstration of these effects on the quantum dot-photonic crystal platform. Finally, we will focus on the applications of such cavity QED effects.

  6. Nontoxic quantum dot research improves solar cells

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645U.S. DOE Office of Science (SC)Integrated CodesTransparencyDOE Project Taps HPCNew4OrganicNontoxic quantum dot

  7. Temperature Dependence of Single CdSe/ZnS Quantum Dots Luminescence Lifetime

    E-Print Network [OSTI]

    Paris-Sud XI, Université de

    , such as quantum dots (QDs), has grown dramatically. These semiconductor QDs bridge the gap between single

  8. Location deterministic biosensing from quantum-dot-nanowire assemblies

    SciTech Connect (OSTI)

    Liu, Chao [Materials Science and Engineering Program, Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712 (United States); Kim, Kwanoh [Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Fan, D. L., E-mail: dfan@austin.utexas.edu [Materials Science and Engineering Program, Texas Materials Institute, University of Texas at Austin, Austin, Texas 78712 (United States); Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States)

    2014-08-25T23:59:59.000Z

    Semiconductor quantum dots (QDs) with high fluorescent brightness, stability, and tunable sizes, have received considerable interest for imaging, sensing, and delivery of biomolecules. In this research, we demonstrate location deterministic biochemical detection from arrays of QD-nanowire hybrid assemblies. QDs with diameters less than 10?nm are manipulated and precisely positioned on the tips of the assembled Gold (Au) nanowires. The manipulation mechanisms are quantitatively understood as the synergetic effects of dielectrophoretic (DEP) and alternating current electroosmosis (ACEO) due to AC electric fields. The QD-nanowire hybrid sensors operate uniquely by concentrating bioanalytes to QDs on the tips of nanowires before detection, offering much enhanced efficiency and sensitivity, in addition to the position-predictable rationality. This research could result in advances in QD-based biomedical detection and inspires an innovative approach for fabricating various QD-based nanodevices.

  9. Chains of quantum dot molecules grown on Si surface pre-patterned by ion-assisted nanoimprint lithography

    SciTech Connect (OSTI)

    Smagina, Zh. V.; Stepina, N. P., E-mail: stepina@isp.nsc.ru; Zinovyev, V. A.; Kuchinskaya, P. A. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novikov, P. L.; Dvurechenskii, A. V. [Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Lavrenteva 13, 630090 Novosibirsk (Russian Federation); Novosibirsk State University, Pirogova, 2, 630090 Novosibirsk (Russian Federation)

    2014-10-13T23:59:59.000Z

    An original approach based on the combination of nanoimprint lithography and ion irradiation through mask has been developed for fabrication of large-area periodical pattern on Si(100). Using the selective etching of regions amorphized by ion irradiation ordered structures with grooves and ridges were obtained. The shape and depth of the relief were governed by ion energy and by the number of etching stages as well. Laterally ordered chains of Ge quantum dots were fabricated by molecular beam epitaxy of Ge on the pre-patterned Si substrates. For small amount of Ge deposited chains contain separate quantum dot molecules. The increase of deposition amount leads to overlapping of quantum dot molecules with formation of dense homogeneous chains of quantum dots. It was shown that the residual irradiation-induced bulk defects underneath the grooves suppress nucleation of Ge islands at the bottom of grooves. On pre-patterned substrates with whole defect regions, etched quantum dots grow at the bottom of grooves. The observed location of Ge quantum dots is interpreted in terms of local strain-mediated surface chemical potential which controls the sites of islands nucleation. The local chemical potential is affected by additional strain formed by the residual defects. It was shown by molecular dynamics calculations that these defects form the compressive strain at the bottom of grooves.

  10. Competing interactions in semiconductor quantum dots

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    van den Berg, R.; Brandino, G. P.; El Araby, O.; Konik, R. M.; Gritsev, V.; Caux, J. -S.

    2014-10-01T23:59:59.000Z

    We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. Onmore »the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.« less

  11. Competing interactions in semiconductor quantum dots

    DOE Public Access Gateway for Energy & Science Beta (PAGES Beta)

    van den Berg, R. [Univ. of Amsterdam (Netherlands). Inst. for Theoretical Physics; Brandino, G. P. [Univ. of Amsterdam (Netherlands). Inst. for Theoretical Physics; El Araby, O. [Univ. of Amsterdam (Netherlands). Inst. for Theoretical Physics; Konik, R. M. [Brookhaven National Lab. (BNL), Upton, NY (United States); Gritsev, V. [Univ. of Amsterdam (Netherlands). Inst. for Theoretical Physics; Caux, J. -S. [Univ. of Amsterdam (Netherlands). Inst. for Theoretical Physics

    2014-10-01T23:59:59.000Z

    We introduce an integrability-based method enabling the study of semiconductor quantum dot models incorporating both the full hyperfine interaction as well as a mean-field treatment of dipole-dipole interactions in the nuclear spin bath. By performing free induction decay and spin echo simulations we characterize the combined effect of both types of interactions on the decoherence of the electron spin, for external fields ranging from low to high values. We show that for spin echo simulations the hyperfine interaction is the dominant source of decoherence at short times for low fields, and competes with the dipole-dipole interactions at longer times. On the contrary, at high fields the main source of decay is due to the dipole-dipole interactions. In the latter regime an asymmetry in the echo is observed. Furthermore, the non-decaying fraction previously observed for zero field free induction decay simulations in quantum dots with only hyperfine interactions, is destroyed for longer times by the mean-field treatment of the dipolar interactions.

  12. Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna

    E-Print Network [OSTI]

    Krishna, Sanjay

    Photovoltaic quantum dot quantum cascade infrared photodetector A. V. Barve and S. Krishna Citation subject to AIP license or copyright; see http://apl.aip.org/about/rights_and_permissions #12;Photovoltaic) Design and characterization of a quantum dot quantum cascade detector for photovoltaic midwave infrared

  13. Minimal Self-Contained Quantum Refrigeration Machine Based on Four Quantum Dots

    E-Print Network [OSTI]

    Davide Venturelli; Rosario Fazio; Vittorio Giovannetti

    2013-06-22T23:59:59.000Z

    We present a theoretical study of an electronic quantum refrigerator based on four quantum dots arranged in a square configuration, in contact with as many thermal reservoirs. We show that the system implements the basic minimal mechanism for acting as a self-contained quantum refrigerator, by demonstrating heat extraction from the coldest reservoir and the cooling of the nearby quantum-dot.

  14. Entanglement distribution for a practical quantum-dot-based quantum processor architecture

    E-Print Network [OSTI]

    Timothy P. Spiller; Irene D'Amico; Brendon W. Lovett

    2007-04-13T23:59:59.000Z

    We propose a quantum dot architecture for enabling universal quantum information processing. Quantum registers, consisting of arrays of vertically stacked self-assembled semiconductor quantum dots, are connected by chains of in-plane self-assembled dots. We propose an entanglement distributor, a device for producing and distributing maximally entangled qubits on demand, communicated through in-plane dot chains. This enables the transmission of entanglement to spatially separated register stacks, providing a resource for the realisation of a sizeable quantum processor built from coupled register stacks of practical size. Our entanglement distributor could be integrated into many of the present proposals for self-assembled quantum dot-based quantum computation. Our device exploits the properties of simple, relatively short, spin-chains and does not require microcavities. Utilizing the properties of self-assembled quantum dots, after distribution the entanglement can be mapped into relatively long lived spin qubits and purified, providing a flexible, distributed, off-line resource.

  15. Linewidth broadening of a quantum dot coupled to an off-resonant cavity

    E-Print Network [OSTI]

    Arka Majumdar; Andrei Faraon; Erik Kim; Dirk Englund; Hyochul Kim; Pierre Petroff; Jelena Vuckovic

    2010-03-11T23:59:59.000Z

    We study the coupling between a photonic crystal cavity and an off-resonant quantum dot under resonant excitation of the cavity or the quantum dot. Linewidths of the quantum dot and the cavity as a function of the excitation laser power are measured. We show that the linewidth of the quantum dot, measured by observing the cavity emission, is significantly broadened compared to the theoretical estimate. This indicates additional incoherent coupling between the quantum dot and the cavity.

  16. The impact of disorder on charge transport in three dimensional quantum dot resonant tunneling structures

    SciTech Connect (OSTI)

    Puthen-Veettil, B., E-mail: b.puthen-veettil@unsw.edu.au; Patterson, R.; König, D.; Conibeer, G.; Green, M. A. [Australian Centre for Advanced Photovoltaics, UNSW, Sydney 2052 (Australia)

    2014-10-28T23:59:59.000Z

    Efficient iso-entropic energy filtering of electronic waves can be realized through nanostructures with three dimensional confinement, such as quantum dot resonant tunneling structures. Large-area deployment of such structures is useful for energy selective contacts but such configuration is susceptible to structural disorders. In this work, the transport properties of quantum-dot-based wide-area resonant tunneling structures, subject to realistic disorder mechanisms, are studied. Positional variations of the quantum dots are shown to reduce the resonant transmission peaks while size variations in the device are shown to reduce as well as broaden the peaks. Increased quantum dot size distribution also results in a peak shift to lower energy which is attributed to large dots dominating transmission. A decrease in barrier thickness reduces the relative peak height while the overall transmission increases dramatically due to lower “series resistance.” While any shift away from ideality can be intuitively expected to reduce the resonance peak, quantification allows better understanding of the tolerances required for fabricating structures based on resonant tunneling phenomena/.

  17. Designing Small Silicon Quantum Dots with Low Reorganization Energy

    E-Print Network [OSTI]

    Zang, Xiaoning

    2015-01-01T23:59:59.000Z

    A first principles, excited state analysis is carried out to identify ways of producing silicon quantum dots with low excitonic reorganization energy. These focus on the general strategy of either reducing or constraining exciton-phonon coupling, and four approaches are explored. The results can be implemented in quantum dot solids to mitigate polaronic effects and increase the lifetime of coherent excitonic superpositions. It is demonstrated that such designs can also be used to alter the shape of the spectral density for reorganization so as to reduce the rates of both decoherence and dissipation. The results suggest that it may be possible to design quantum dot solids that support partially coherent exciton transport.

  18. Factorization of Dirac Equation and Graphene Quantum Dot

    E-Print Network [OSTI]

    Youness Zahidi; Ahmed Jellal; Hocine Bahlouli; Mohammed El Bouziani

    2014-05-14T23:59:59.000Z

    We consider a quantum dot described by a cylindrically symmetric 2D Dirac equation. The potentials representing the quantum dot are taken to be of different types of potential configuration, scalar, vector and pseudo-scalar to enable us to enrich our study. Using various potential configurations, we found that in the presence of a mass term an electrostatically confined quantum dot can accommodate true bound states, which is in agreement with previous work. The differential cross section associated with one specific potential configuration has been computed and discussed as function of the various potential parameters.

  19. Steering of a Bosonic Mode with a Double Quantum Dot

    E-Print Network [OSTI]

    T. Brandes; N. Lambert

    2003-02-13T23:59:59.000Z

    We investigate the transport and coherence properties of a double quantum dot coupled to a single damped boson mode. Our numerically results reveal how the properties of the boson distribution can be steered by altering parameters of the electronic system such as the energy difference between the dots. Quadrature amplitude variances and the Wigner function are employed to illustrate how the state of the boson mode can be controlled by a stationary electron current through the dots.

  20. Optimal tunneling enhances the quantum photovoltaic effect in double quantum dots

    E-Print Network [OSTI]

    Wang, Chen

    We investigate the quantum photovoltaic effect in double quantum dots by applying the nonequilibrium quantum master equation. A drastic suppression of the photovoltaic current is observed near the open circuit voltage, ...

  1. Temperature-Dependent Electron Transport in Quantum Dot Photovoltaics

    E-Print Network [OSTI]

    Padilla, Derek

    2013-01-01T23:59:59.000Z

    to enhanced photovoltaic device efficiency. ACS nano, 2(11):Photovoltaic Devices Introduction Thin-film quantum dot (QD) photovoltaics provide the potential to create high-efficiencyefficiency under such illumina- tion. A non-ideal model of a photovoltaic

  2. Engineering a Robust Photovoltaic Device with Quantum Dots and Bacteriorhodopsin

    E-Print Network [OSTI]

    Renugopalakrishnan, Venkatesan

    We present a route toward a radical improvement in solar cell efficiency using resonant energy transfer and sensitization of semiconductor metal oxides with a light-harvesting quantum dot (QD)/bacteriorhodopsin (bR) layer ...

  3. Quantum Dot Tracers for Use in Engineered Geothermal Systems

    Broader source: Energy.gov [DOE]

    DOE Geothermal Peer Review 2010 - Presentation. Project objective: To develop and demonstrate a new class of tracers?semiconductor nanoparticles(quantum dots)?that offer great promise for use in characterizing fracture networks in EGS reservoirs.

  4. Self-Sustaining Dynamical Nuclear Polarization Oscillations in Quantum Dots

    E-Print Network [OSTI]

    Rudner, M. S.

    Early experiments on spin-blockaded double quantum dots revealed robust, large-amplitude current oscillations in the presence of a static (dc) source-drain bias. Despite experimental evidence implicating dynamical nuclear ...

  5. Study of field driven electroluminescence in colloidal quantum dot solids

    E-Print Network [OSTI]

    Bozyigit, Deniz

    Semiconductor nanocrystals, or quantum dots(QDs), promise to drive advances in electronic light generation. It was recently shown that long range transport of charge, which is typically required for electric excitation and ...

  6. Hybrid organic/quantum dot thin film structures and devices

    E-Print Network [OSTI]

    Coe-Sullivan, Seth (Seth Alexander)

    2005-01-01T23:59:59.000Z

    Organic light emitting diodes have undergone rapid advancement over the course of the past decade. Similarly, quantum dot synthesis has progressed to the point that room temperature highly efficient photoluminescence can ...

  7. Local droplet etching – Nanoholes, quantum dots, and air-gap heterostructures

    SciTech Connect (OSTI)

    Heyn, Ch.; Sonnenberg, D.; Graf, A.; Kerbst, J.; Stemmann, A.; Hansen, W. [Institute of Applied Physics, University of Hamburg, Jungiusstr. 11, 20355 Hamburg (Germany)

    2014-05-15T23:59:59.000Z

    Local droplet etching (LDE) allows the self-organized generation of nanoholes in semiconductor surfaces and is fully compatible with molecular beam epitaxy (MBE). The influence of the process parameters as well as of droplet and substrate materials on the LDE nanohole morphology is discussed. Furthermore, recent applications of LDE, the fabrication of quantum dots by hole filling and the creation of air-gap heterostructures are addressed.

  8. Fluorescence from a quantum dot and metallic nanosphere hybrid system

    SciTech Connect (OSTI)

    Schindel, Daniel G. [Department of Mathematics and Statistics, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB, R3B 2E9 (Canada); Singh, Mahi R. [Department of Physics and Astronomy, University of Western Ontario, 1151 Richmond Street, London, ON, N6A 3K7 (Canada)

    2014-03-31T23:59:59.000Z

    We present energy absorption and interference in a quantum dot-metallic nanosphere system embedded on a dielectric substrate. A control field is applied to induce dipole moments in the nanosphere and the quantum dot, and a probe field is applied to monitor absorption. Dipole moments in the quantum dot or the metal nanosphere are induced, both by the external fields and by each other's dipole fields. Thus, in addition to direct polarization, the metal nanosphere and the quantum dot will sense one another via the dipole-dipole interaction. The density matrix method was used to show that the absorption spectrum can be split from one peak to two peaks by the control field, and this can also be done by placing the metal sphere close to the quantum dot. When the two are extremely close together, a self-interaction in the quantum dot produces an asymmetry in the absorption peaks. In addition, the fluorescence efficiency can be quenched by the addition of a metal nanosphere. This hybrid system could be used to create ultra-fast switching and sensing nanodevices.

  9. Double superexchange in quantum dot mesomaterials

    E-Print Network [OSTI]

    Wu, Zhigang

    of defects,2 and resist oxidation better.3 In addition, these small dots use their slice of the solar. An idea that has been explored for larger dots is to encapsulate them within an inorganic amorphous matrix yet to be achieved. A second approach is to encapsulate the dots within an organic polymer blend.12

  10. Green route synthesis of high quality CdSe quantum dots for applications in light emitting devices

    SciTech Connect (OSTI)

    Bera, Susnata, E-mail: susnata.bera@gmail.com [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Singh, Shashi B. [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India); Ray, S.K., E-mail: physkr@phy.iitkgp.ernet.in [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

    2012-05-15T23:59:59.000Z

    Investigation was made on light emitting diodes fabricated using CdSe quantum dots. CdSe quantum dots were synthesized chemically using olive oil as the capping agent, instead of toxic phosphine. Room temperature photoluminescence investigation showed sharp 1st excitonic emission peak at 568 nm. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting devices were fabricated by solution process. The electroluminescence study showed low turn on voltage ({approx}2.2 V) .The EL peak intensity was found to increase by increasing the operating current. - Graphical abstract: Light emitting diode was fabricated using CdSe quantum dots using olive oil as the capping agent, instead of toxic phosphine. Bi-layer organic/inorganic (P3HT/CdSe) hybrid light emitting device shows strong electroluminescence in the range 630-661 nm. Highlights: Black-Right-Pointing-Pointer CdSe Quantum dots were synthesized using olive oil as the capping agent. Black-Right-Pointing-Pointer Light emitting device was fabricated using CdSe QDs/P3HT polymer heterojunction. Black-Right-Pointing-Pointer The I-V characteristics study showed low turn on voltage at {approx}2.2 V. Black-Right-Pointing-Pointer The EL peak intensity increases with increasing the operating current.

  11. High excitation power photoluminescence studies of ultra-low density GaAs quantum dots

    SciTech Connect (OSTI)

    Sonnenberg, D.; Graf, A.; Paulava, V.; Heyn, Ch.; Hansen, W. [Institut für Angewandte Physik und Zentrum für Mikrostrukturforschung, Universität Hamburg, Jungiusstr. 11, 20355 Hamburg (Germany)

    2013-12-04T23:59:59.000Z

    We fabricate GaAs epitaxial quantum dots (QDs) by filling of self-organized nanoholes in AlGaAs. The QDs are fabricated under optimized process conditions and have ultra-low density in the 10{sup 6} cm{sup ?2} regime. At low excitation power the optical emission of single QDs exhibit sharp excitonic lines, which are attributed to the recombination of excitonic and biexcitonic states. High excitation power measurements reveal surprisingly broad emission lines from at least six QD shell states.

  12. Electrically-protected resonant exchange qubits in triple quantum dots

    E-Print Network [OSTI]

    J. M. Taylor; V. Srinivasa; J. Medford

    2013-04-12T23:59:59.000Z

    We present a modulated microwave approach for quantum computing with qubits comprising three spins in a triple quantum dot. This approach includes single- and two-qubit gates that are protected against low-frequency electrical noise, due to an operating point with a narrowband response to high frequency electric fields. Furthermore, existing double quantum dot advances, including robust preparation and measurement via spin-to-charge conversion, are immediately applicable to the new qubit. Finally, the electric dipole terms implicit in the high frequency coupling enable strong coupling with superconducting microwave resonators, leading to more robust two-qubit gates.

  13. Nonclassical Radiation from a Single Quantum Dot P. Michler1

    E-Print Network [OSTI]

    Buratto, Steve

    Nonclassical Radiation from a Single Quantum Dot P. Michler1 ) (a, b), A. Imamoglu (a), A. Kiraz (a nature of radiation and provides direct evi- dence that the emission source is a single two-level quantum of a single atom in an atomic beam [1] and from a single ion which has been stored in a radiofrequency trap [2

  14. Low-Cost Photovoltaics: Luminescent Solar Concentrators And Colloidal Quantum Dot Solar Cells

    E-Print Network [OSTI]

    Leow, Shin Woei

    2014-01-01T23:59:59.000Z

    enhancing the efficiency of solar cells and extending theirA. J. Nozik, “Quantum dot solar cells,” Phys. E Low-Dimens.oxide PbS quantum dot solar cells at low temperature,” Appl.

  15. An Investigation on Gel Electrophoresis with Quantum Dots End-labeled DNA

    E-Print Network [OSTI]

    Chen, Xiaojia

    2009-05-15T23:59:59.000Z

    explored manipulating DNA fragments by end labeling DNA molecules with quantum dot nanocrystals. The quantum dot-DNA conjugates can be further modified through binding interactions with biotinylated single-stranded DNA primers. Single molecule visualization...

  16. Liquid-phase plasma synthesis of silicon quantum dots embedded in carbon matrix for lithium battery anodes

    SciTech Connect (OSTI)

    Wei, Ying [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); College of Chemistry and Chemical Engineering, Bohai University, Jinzhou 121000 (China); Yu, Hang; Li, Haitao; Ming, Hai; Pan, Keming; Huang, Hui [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); Liu, Yang, E-mail: yangl@suda.edu.cn [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China); Kang, Zhenhui, E-mail: zhkang@suda.edu.cn [Institute of Functional Nano and Soft Materials (FUNSOM) and Jiangsu Key Laboratory for Carbon-Based Functional Materials and Devices, Soochow University, Suzhou (China)

    2013-10-15T23:59:59.000Z

    Graphical abstract: - Highlights: • Silicon quantum dots embedded in carbon matrix (SiQDs/C) were fabricated. • SiQDs/C exhibits excellent battery performance as anode materials with high specific capacity. • The good performance was attributed to the marriage of small sized SiQDs and carbon. - Abstract: Silicon quantum dots embedded in carbon matrix (SiQDs/C) nanocomposites were prepared by a novel liquid-phase plasma assisted synthetic process. The SiQDs/C nanocomposites were demonstrated to show high specific capacity, good cycling life and high coulmbic efficiency as anode materials for lithium-ion battery.

  17. Efficient photon extraction from a quantum dot in a broad-band planar cavity antenna

    SciTech Connect (OSTI)

    Ma, Yong, E-mail: y.ma@hw.ac.uk; Kremer, Peter E.; Gerardot, Brian D., E-mail: B.D.Gerardot@hw.ac.uk [Institute of Photonics and Quantum Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS (United Kingdom)

    2014-01-14T23:59:59.000Z

    We analyse the extraction of photons emitted from single InAs quantum dots embedded in planar microcavities. The structures are designed to achieve broad-band operation and high-collection efficiency from a device requiring straightforward fabrication, even with electrical contacts. The designs consist of a quantum dot in a GaAs membrane with asymmetric top and bottom mirrors and a top-side solid immersion lens (SIL). Four separate cases are considered in our design: a GaAs membrane only (case 1), GaAs membrane with a glass SIL on top (case 2), a GaAs membrane with a glass SIL on top and a back mirror consisting of Au (case 3), a GaAs membrane with a glass SIL on top of a distribute Bragg reflector mirror and Au back mirror (case 4). Both finite difference time domain and analytical simulations are used to calculate the electric field, power density, and far-field radiation pattern. For optimized structures (case 4), we obtain significant extraction efficiencies (>50%) with modest Purcell enhancements (?20%) and a large spectral full-width-half-maximum (>100?nm). The high-extraction efficiency, broad-band operation, and facile fabrication make the proposed structures promising for realistic quantum dot devices.

  18. Intermediate-band photosensitive device with quantum dots having tunneling barrier embedded in organic matrix

    DOE Patents [OSTI]

    Forrest, Stephen R. (Ann Arbor, MI)

    2008-08-19T23:59:59.000Z

    A plurality of quantum dots each have a shell. The quantum dots are embedded in an organic matrix. At least the quantum dots and the organic matrix are photoconductive semiconductors. The shell of each quantum dot is arranged as a tunneling barrier to require a charge carrier (an electron or a hole) at a base of the tunneling barrier in the organic matrix to perform quantum mechanical tunneling to reach the respective quantum dot. A first quantum state in each quantum dot is between a lowest unoccupied molecular orbital (LUMO) and a highest occupied molecular orbital (HOMO) of the organic matrix. Wave functions of the first quantum state of the plurality of quantum dots may overlap to form an intermediate band.

  19. Cost-Effective Fabrication Routes for the Production of Quantum...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Production of Quantum Well Type Structures and Recovery of Waste Heat from Heavy Duty Trucks Cost-Effective Fabrication Routes for the Production of Quantum Well Type Structures...

  20. Coherent excitation of a strongly coupled quantum dot - cavity system

    E-Print Network [OSTI]

    Dirk Englund; Arka Majumdar; Andrei Faraon; Mitsuru Toishi; Nick Stoltz; Pierre Petroff; Jelena Vuckovic

    2009-02-19T23:59:59.000Z

    We have studied the coherent excitation of a strongly coupled QD/photonic crystal cavity system. Time-resolved reflectivity measurements show the vacuum Rabi oscillation of the dot in the cavity. Next, we considered the resonant driving of a cavity-detuned dot, which efficiently populates the cavity mode. This cavity-controlled read-out channel allows high-resolution single quantum dot spectroscopy. Autocorrelation measurements on the cavity mode show antibunching and suggest the use of the resonantly driven QD/cavity system as an on-demand source of single photons with potentially near-unity indistinguishability.

  1. Reducing charge trapping in PbS colloidal quantum dot solids

    SciTech Connect (OSTI)

    Balazs, D. M.; Nugraha, M. I.; Bisri, S. Z.; Loi, M. A., E-mail: m.a.loi@rug.nl [Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4, Groningen 9747AG (Netherlands); Sytnyk, M.; Heiss, W. [Institute for Semiconductor and Solid State Physics, University of Linz, Altenbergerstr. 69, Linz 4040 (Austria)

    2014-03-17T23:59:59.000Z

    Understanding and improving charge transport in colloidal quantum dot solids is crucial for the development of efficient solar cells based on these materials. In this paper, we report high performance field-effect transistors based on lead-sulfide colloidal quantum dots (PbS CQDs) crosslinked with 3-mercaptopropionic acid (MPA). Electron mobility up to 0.03 cm{sup 2}/Vs and on/off ratio above 10{sup 5} was measured; the later value is the highest in the literature for CQD Field effect transistors with silicon-oxide gating. This was achieved by using high quality material and preventing trap generation during fabrication and measurement. We show that air exposure has a reversible p-type doping effect on the devices, and that intrinsically MPA is an n-type dopant for PbS CQDs.

  2. Final LDRD report : infrared detection and power generation using self-assembled quantum dots.

    SciTech Connect (OSTI)

    Cederberg, Jeffrey George; Ellis, Robert; Shaner, Eric Arthur

    2008-02-01T23:59:59.000Z

    Alternative solutions are desired for mid-wavelength and long-wavelength infrared radiation detection and imaging arrays. We have investigated quantum dot infrared photodetectors (QDIPs) as a possible solution for long-wavelength infrared (8 to 12 {mu}m) radiation sensing. This document provides a summary for work done under the LDRD 'Infrared Detection and Power Generation Using Self-Assembled Quantum Dots'. Under this LDRD, we have developed QDIP sensors and made efforts to improve these devices. While the sensors fabricated show good responsivity at 80 K, their detectivity is limited by high noise current. Following efforts concentrated on how to reduce or eliminate this problem, but with no clear path was identified to the desired performance improvements.

  3. A highly efficient (>6%) Cd1xMnxSe quantum dot sensitized solar cell

    E-Print Network [OSTI]

    Cao, Guozhong

    A highly efficient (>6%) Cd1ÀxMnxSe quantum dot sensitized solar cell Jianjun Tian,*a Lili Lv,a Chengbin Fei,b Yajie Wang,b Xiaoguang Liua and Guozhong Cao*bc Quantum dot sensitized solar cells (QDSCs-effective solar cell. The design and synthesis of quantum dots (QDs) for achieving high photoelectric performance

  4. Properties of GaN and ZnO Quantum Dots

    E-Print Network [OSTI]

    CHAPTER 3 Properties of GaN and ZnO Quantum Dots Vladimir A. Fonoberov, Alexander A. Balandin Nano. GaN Quantum Dots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 120 2.1. Electron and Hole States in Strained Wurtzite and Zincblende GaN Quantum Dots

  5. Temperature-Tuning of Near-Infrared Monodisperse Quantum Dot Solids at

    E-Print Network [OSTI]

    Hone, James

    include solar energy conversion as well as quantum communication. In quantum dot systems, the dot sizes photovoltaics, capturing the infrared spectrum, and also exhibiting possible multi- exciton generation.4. Incoherent Fo¨rster resonance energy transfer (FRET) 8­11 can occur between different-sized quantum dots

  6. Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas

    E-Print Network [OSTI]

    Coppersmith, Susan N.

    Quantum dots and etch-induced depletion of a silicon two-dimensional electron gas L. J. Klein, K. L coupled quantum dots containing individual electrons whose spins act as qubits.4 We have made recent in a silicon quantum dot can be held constant for up to 11 hours. This fulfills an important milestone towards

  7. Arrays of nanoscale magnetic dots: Fabrication by x-ray interference lithography and characterization

    SciTech Connect (OSTI)

    Heyderman, L.J.; Solak, H.H.; David, C.; Atkinson, D.; Cowburn, R.P.; Nolting, F. [Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland); Nanomagnetism Group, Department of Physics, University of Durham, Rochester Building, Science Laboratories, South Road, Durham DH1 3LE (United Kingdom); Swiss Light Source, Paul Scherrer Institut, CH-5232 Villigen PSI (Switzerland)

    2004-11-22T23:59:59.000Z

    X-ray interference lithography (XIL) was employed in combination with electrodeposition to fabricate arrays of nanoscale nickel dots which are uniform over 40 {mu}m and have periods down to 71 nm. Using extreme-ultraviolet light, XIL has the potential to produce magnetic dot arrays over large areas with periods well below 50 nm, and down to a theoretical limit of 6.5 nm for a 13 nm x-ray wavelength. In the nickel dot arrays, we observed the effect of interdot magnetic stray field interactions. Measuring the hysteresis loops using the magneto-optical Kerr effect, a double switching via the vortex state was observed in the nickel dots with diameters down to 44 nm and large dot separations. As the dot separations are reduced to below around 50 nm a single switching, occurring by collective rotation of the magnetic spins, is favored due to interdot magnetic stray field interactions. This results in magnetic flux closure through several dots which could be visualized with micromagnetic simulations. Further evidence of the stray field interactions was seen in photoemission electron microscopy images, where bands of contrast corresponding to chains of coupled dots were observed.

  8. Photovoltaic performance of ultra-small PbSe quantum dots

    E-Print Network [OSTI]

    Ma, Wanli

    2014-01-01T23:59:59.000Z

    Y; Alivisatos, AP, Photovoltaic Devices Employing TernaryPhotovoltaic performance of ultra-small PbSe quantum dotsquantum dot, solar cell, photovoltaic, quantum size effect

  9. Simulations of the spontaneous emission of a quantum dot near a gap plasmon waveguide

    SciTech Connect (OSTI)

    Perera, Chamanei S., E-mail: cp.hettiarachchige@qut.edu.au; Vernon, Kristy C.; Mcleod, Angus [Plasmonic Device Group, Queensland University of Technology, GPO box 2434, Brisbane, Queensland (Australia)

    2014-02-07T23:59:59.000Z

    In this paper, we modeled a quantum dot at near proximity to a gap plasmon waveguide to study the quantum dot-plasmon interactions. Assuming that the waveguide is single mode, this paper is concerned about the dependence of spontaneous emission rate of the quantum dot on waveguide dimensions such as width and height. We compare coupling efficiency of a gap waveguide with symmetric configuration and asymmetric configuration illustrating that symmetric waveguide has a better coupling efficiency to the quantum dot. We also demonstrate that optimally placed quantum dot near a symmetric waveguide with 50?nm?×?50?nm cross section can capture 80% of the spontaneous emission into a guided plasmon mode.

  10. Photon-Assisted Tunneling in a Carbon Nanotube Quantum Dot

    E-Print Network [OSTI]

    not use highly doped Si to avoid leakage of the high- frequency signal to the back gate. The quantum dot is formed between aluminum source/drain contacts, and the potential can be tuned using an aluminum side to source and drain contacts. To transport the microwave signal to the device, we use semirigid coaxial

  11. Quantum Dot-Aptamer Conjugates for Synchronous Cancer Imaging, Therapy,

    E-Print Network [OSTI]

    Zhang, Liangfang

    a novel quantum dot (QD)-aptamer(Apt)-doxorubicin (Dox) conjugate [QD-Apt(Dox)] as a targeted cancer of prostate cancer cells that express the PSMA protein. The intercalation of Dox, a widely used antineoplastic in a targeted QD-Apt(Dox) conjugate with reversible self- quenching properties based on a Bi-FRET mechanism

  12. Quantum dot-based nanomaterials for biological imaging

    E-Print Network [OSTI]

    Zimmer, John P. (John Philip)

    2006-01-01T23:59:59.000Z

    Quantum dot-based fluorescent probes were synthesized and applied to biological imaging in two distinct size regimes: (1) 100-1000 nm and (2) < 10 nm in diameter. The larger diameter range was accessed by doping CdSe/ZnS ...

  13. Supplementary Document CdSe quantum dot synthesis

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    , TOP (Sigma Aldrich) have been used as pure as supplied from the companies without further purification solar cell The reflection measurements have been carried out for the nanopillar solar cells before that the reflection of Si nanopillar solar cells drops off with the integration of quantum dots by 9-14%, which shows

  14. Solution-processed high-performance colloidal quantum dot tandem photodetectors on flexible substrates

    SciTech Connect (OSTI)

    Jiang, Zhenyu; You, Guanjun; Wang, Li; Liu, Jie; Xu, Jian, E-mail: jianxu@engr.psu.edu [Department of Engineering Science and Mechanics, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Hu, Wenjia [China Tianchen Engineering Corporation, Tianjin 300400 (China); Zhang, Yu [State Key Laboratory on Integrated Optoelectronics and College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China)

    2014-08-28T23:59:59.000Z

    We report a high-performance colloidal quantum dot (CQD)-based near-infrared tandem photodetector fabricated on flexible substrates via solution-processed method. The tandem photodetector on poly(ethylene terephthalate) substrates exhibited low dark current and high detectivities over ?8.8?×?10{sup 11} Jones at near infrared range at ?0.5?V bias and over ?10{sup 13} Jones near 0 bias. The critical bend radii of ?8?mm and ?3?mm have been demonstrated for tensile and compressive bending, respectively. The performance of photodetectors remains stable under mechanical stress, making PbSe CQD material a promise candidate for flexible infrared sensing applications.

  15. High performance continuous wave 1.3??m quantum dot lasers on silicon

    SciTech Connect (OSTI)

    Liu, Alan Y., E-mail: ayliu01@engineering.ucsb.edu; Norman, Justin [Materials Department, University of California Santa Barbara, California 93106 (United States); Zhang, Chong [Department of Electrical and Computer Engineering, University of California Santa Barbara, California 93106 (United States); Snyder, Andrew; Lubyshev, Dmitri; Fastenau, Joel M.; Liu, Amy W. K. [IQE, Inc., Bethlehem, Pennsylvania 18015 (United States); Gossard, Arthur C.; Bowers, John E. [Materials Department, University of California Santa Barbara, California 93106 (United States); Department of Electrical and Computer Engineering, University of California Santa Barbara, California 93106 (United States)

    2014-01-27T23:59:59.000Z

    We demonstrate record performance 1.3??m InAs quantum dot lasers grown on silicon by molecular beam epitaxy. Ridge waveguide lasers fabricated from the as-grown material achieve room temperature continuous wave thresholds as low as 16?mA, output powers exceeding 176 mW, and lasing up to 119?°C. P-modulation doping of the active region improves T{sub 0} to the range of 100–200?K while maintaining low thresholds and high output powers. Device yield is presented showing repeatable performance across different dies and wafers.

  16. Double-Dot Quantum Ratchet Driven by an Independently Biased Quantum Point Contact V. S. Khrapai,1,2

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    Double-Dot Quantum Ratchet Driven by an Independently Biased Quantum Point Contact V. S. Khrapai,1 of the two quantum dots. The results are interpreted in terms of a quantum ratchet phenomenon in a DQD possessing current be- cause of broken spatial symmetry, so-called ratchets, ap- pear in a variety

  17. NREL Certifies First All-Quantum-Dot Photovoltaic Cell; Demonstrates Stability, Performance (Fact Sheet)

    SciTech Connect (OSTI)

    Not Available

    2011-02-01T23:59:59.000Z

    Researchers at the National Renewable Energy Laboratory (NREL) have certified the first all-quantum-dot photovoltaic cell, which was based on lead sulfide and demonstrated reasonable quantum dot solar cell performance for an initial efficiency measurement along with good stability. The certified open-circuit voltage of the quantum dot cell is greater than that possible from bulk lead sulfide because of quantum confinement.

  18. Cooling an electron gas using quantum dot based electronic refrigeration

    E-Print Network [OSTI]

    Prance, Jonathan Robert

    2009-10-13T23:59:59.000Z

    Cooling an electron gas using quantum dot based electronic refrigeration Jonathan Robert Prance August 28, 2009 Downing College, University of Cambridge A thesis submitted for the degree of Doctor of Philosophy Preface The work presented... dots. Conventionally, low temperature measurements of 2DEGs are made by cooling the sample to 1.5 K with liquid Helium-4, to 300 mK with liquid Helium-3, or even down to a few mK using a dilution refrigerator. However, at lower temperatures the electron...

  19. Photoconductivity of Si/Ge multilayer structures with Ge quantum dots pseudomorphic to the Si matrix

    SciTech Connect (OSTI)

    Talochkin, A. B., E-mail: tal@thermo.isp.nsc.ru; Chistokhin, I. B. [Russian Academy of Sciences, Rzhanov Institute of Semiconductor Physics, Siberian Branch (Russian Federation)

    2011-07-15T23:59:59.000Z

    Longitudinal photoconductivity spectra of Si/Ge multilayer structures with Ge quantum dots grown pseudomorphically to the Si matrix are studied. Lines of optical transitions between hole levels of quantum dots and Si electronic states are observed. This allowed us to construct a detailed energy-level diagram of electron-hole levels of the structure. It is shown that hole levels of pseudomorphic Ge quantum dots are well described by the simplest 'quantum box' model using actual sizes of Ge islands. The possibility of controlling the position of the long-wavelength photosensitivity edge by varying the growth parameters of Si/Ge structures with Ge quantum dots is determined.

  20. Ordered quantum dot molecules and single quantum dots formed by self-organized anisotropic strain engineering

    SciTech Connect (OSTI)

    Lippen, T. van; Noetzel, R.; Hamhuis, G.J.; Wolter, J.H. [European Institute of Telecommunication Technologies/Communication Technology, Basic Research and Applications (eiTT/COBRA) Inter-University Research Institute, Eindhoven University of Technology, 5600 MB Eindhoven (Netherlands)

    2005-02-15T23:59:59.000Z

    An ordered lattice of lateral InAs quantum dot (QD) molecules is created by self-organized anisotropic strain engineering of an (In,Ga)As/GaAs superlattice (SL) template on GaAs(311)B by molecular-beam epitaxy, constituting a Turing pattern in solid state. The SL template and InAs QD growth conditions, such as the number of SL periods, growth temperatures, amount and composition of deposited (In,Ga)As, and insertion of Al-containing layers, are studied in detail for an optimized QD ordering within and among the InAs QD molecules on the SL template nodes, which is evaluated by atomic force microscopy. The average number of InAs QDs within the molecules is controlled by the thickness of the upper GaAs separation layer on the SL template and the (In,Ga)As growth temperature in the SL. The strain-correlated growth in SL template formation and QD ordering is directly confirmed by high-resolution x-ray diffraction. Ordered arrays of single InAs QDs on the SL template nodes are realized for elevated SL template and InAs QD growth temperatures together with the insertion of a second InAs QD layer. The InAs QD molecules exhibit strong photoluminescence (PL) emission up to room temperature. Temperature-dependent PL measurements exhibit an unusual behavior of the full width at half maximum, indicating carrier redistribution solely within the QD molecules.

  1. Simulation of quantum dots size and spacing effect for intermediate band solar cell application based on InAs quantum dots arrangement in GaAs

    SciTech Connect (OSTI)

    Hendra, P. I. B., E-mail: ib.hendra@gmail.com; Rahayu, F., E-mail: ib.hendra@gmail.com; Darma, Y., E-mail: ib.hendra@gmail.com [Physical Vapor Deposition Laboratory, Physics of Material Electronics Research, Faculty of Mathematics and Natural Sciences, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung 40132 (Indonesia)

    2014-03-24T23:59:59.000Z

    Intermediate band solar cell (IBSC) has become a promising technology in increasing solar cell efficiency. In this work we compare absorption coefficient profile between InAs quantum dots with GaAs bulk. We calculate the efficiency of GaAs bulk and GaAs doped with 2, 5, and 10 nm InAs quantum dot. Effective distances in quantum dot arrangement based on electron tunneling consideration were also calculated. We presented a simple calculation method with low computing power demand. Results showed that arrangement of quantum dot InAs in GaAs can increase solar cell efficiency from 23.9 % initially up to 60.4%. The effective distance between two quantum dots was found 2 nm in order to give adequate distance to prevent electron tunneling and wave functions overlap.

  2. Optical Nonlinearities and Ultrafast Carrier Dynamics in Semiconductor Quantum Dots

    SciTech Connect (OSTI)

    Klimov, V.; McBranch, D.; Schwarz, C.

    1998-08-10T23:59:59.000Z

    Low-dimensional semiconductors have attracted great interest due to the potential for tailoring their linear and nonlinear optical properties over a wide-range. Semiconductor nanocrystals (NC's) represent a class of quasi-zero-dimensional objects or quantum dots. Due to quantum cordhement and a large surface-to-volume ratio, the linear and nonlinear optical properties, and the carrier dynamics in NC's are significantly different horn those in bulk materials. napping at surface states can lead to a fast depopulation of quantized states, accompanied by charge separation and generation of local fields which significantly modifies the nonlinear optical response in NC's. 3D carrier confinement also has a drastic effect on the energy relaxation dynamics. In strongly confined NC's, the energy-level spacing can greatly exceed typical phonon energies. This has been expected to significantly inhibit phonon-related mechanisms for energy losses, an effect referred to as a phonon bottleneck. It has been suggested recently that the phonon bottleneck in 3D-confined systems can be removed due to enhanced role of Auger-type interactions. In this paper we report femtosecond (fs) studies of ultrafast optical nonlinearities, and energy relaxation and trap ping dynamics in three types of quantum-dot systems: semiconductor NC/glass composites made by high temperature precipitation, ion-implanted NC's, and colloidal NC'S. Comparison of ultrafast data for different samples allows us to separate effects being intrinsic to quantum dots from those related to lattice imperfections and interface properties.

  3. Antimony mediated growth of high-density InAs quantum dots for photovoltaic cells

    SciTech Connect (OSTI)

    Tutu, F. K.; Wu, J.; Lam, P.; Tang, M.; Liu, H. [Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE (United Kingdom)] [Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE (United Kingdom); Miyashita, N.; Okada, Y. [Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8904 (Japan)] [Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-Ku, Tokyo 153-8904 (Japan); Wilson, J.; Allison, R. [Defence Science and Technology Laboratory, Portsdown West, Portsdown Hill Road, Fareham Hants PO17 6AD (United Kingdom)] [Defence Science and Technology Laboratory, Portsdown West, Portsdown Hill Road, Fareham Hants PO17 6AD (United Kingdom)

    2013-07-22T23:59:59.000Z

    We report enhanced solar cell performance using high-density InAs quantum dots. The high-density quantum dot was grown by antimony mediated molecular beam epitaxy. In-plane quantum dot density over 1 × 10{sup 11} cm{sup ?2} was achieved by applying a few monolayers of antimony on the GaAs surface prior to quantum dot growth. The formation of defective large clusters was reduced by optimization of the growth temperature and InAs coverage. Comparing with a standard quantum dot solar cell without the incorporation of antimony, the high-density quantum dot solar cell demonstrates a distinct improvement in short-circuit current from 7.4 mA/cm{sup 2} to 8.3 mA/cm{sup 2}.

  4. A Reconfigurable Gate Architecture for Si/SiGe Quantum Dots

    E-Print Network [OSTI]

    D. M. Zajac; T. M. Hazard; X. Mi; K. Wang; J. R. Petta

    2015-02-05T23:59:59.000Z

    We demonstrate a reconfigurable quantum dot gate architecture that incorporates two interchangeable transport channels. One channel is used to form quantum dots and the other is used for charge sensing. The quantum dot transport channel can support either a single or a double quantum dot. We demonstrate few-electron occupation in a single quantum dot and extract charging energies as large as 6.6 meV. Magnetospectroscopy is used to measure valley splittings in the range of 35-70 microeV. By energizing two additional gates we form a few-electron double quantum dot and demonstrate tunable tunnel coupling at the (1,0) to (0,1) interdot charge transition.

  5. Cost-Effective Fabrication Routes for the Productionof Quantum...

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    Productionof Quantum-Well-Type Structures and Recovoery of Waste Heat from Heavy-Duty Trucks Cost-Effective Fabrication Routes for the Productionof Quantum-Well-Type Structures and...

  6. Single-electron shuttle based on a silicon quantum dot

    E-Print Network [OSTI]

    K. W. Chan; M. Mottonen; A. Kemppinen; N. S. Lai; K. Y. Tan; W. H. Lim; A. S. Dzurak

    2011-10-05T23:59:59.000Z

    We report on single-electron shuttling experiments with a silicon metal-oxide-semiconductor quantum dot at 300 mK. Our system consists of an accumulated electron layer at the Si/SiO_2 interface below an aluminum top gate with two additional barrier gates used to deplete the electron gas locally and to define a quantum dot. Directional single-electron shuttling from the source and to the drain lead is achieved by applying a dc source-drain bias while driving the barrier gates with an ac voltage of frequency f_p. Current plateaus at integer levels of ef_p are observed up to f_p = 240 MHz operation frequencies. The observed results are explained by a sequential tunneling model which suggests that the electron gas may be heated substantially by the ac driving voltage.

  7. Resonant scattering of surface plasmon polaritons by dressed quantum dots

    SciTech Connect (OSTI)

    Huang, Danhong; Cardimona, Dave [Air Force Research Laboratory, Space Vehicles Directorate, Kirtland Air Force Base, New Mexico 87117 (United States); Easter, Michelle [Department of Mechanical Engineering, Stevens Institute of Technology, 1 Castle Point Terrace, Hoboken, New Jersey 07030 (United States); Gumbs, Godfrey [Department of Physics and Astronomy, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065 (United States); Maradudin, A. A. [Department of Physics and Astronomy, University of California, Irvine, California 92697 (United States); Lin, Shawn-Yu [Department of Electrical, Computer and Systems Engineering, Rensselaer Polytechnic Institute, 110 8th Street, Troy, New York 12180 (United States); Zhang, Xiang [Department of Mechanical Engineering, 3112 Etcheverry Hall, University of California at Berkeley, Berkeley, California 94720 (United States)

    2014-06-23T23:59:59.000Z

    The resonant scattering of surface plasmon-polariton waves (SPP) by embedded semiconductor quantum dots above the dielectric/metal interface is explored in the strong-coupling regime. In contrast to non-resonant scattering by a localized dielectric surface defect, a strong resonant peak in the spectrum of the scattered field is predicted that is accompanied by two side valleys. The peak height depends nonlinearly on the amplitude of SPP waves, reflecting the feedback dynamics from a photon-dressed electron-hole plasma inside the quantum dots. This unique behavior in the scattered field peak strength is correlated with the occurrence of a resonant dip in the absorption spectrum of SPP waves due to the interband photon-dressing effect. Our result on the scattering of SPP waves may be experimentally observable and applied to spatially selective illumination and imaging of individual molecules.

  8. Enhanced Two-Photon Processes in Quantum Dots inside Photonic Crystal Nanocavities and Quantum Information Processing Applications

    E-Print Network [OSTI]

    Ziliang Lin; Jelena Vuckovic

    2009-07-02T23:59:59.000Z

    We show that the two-photon transition rates of quantum dots coupled to nanocavities are enhanced by up to 8 orders of magnitude relative to quantum dots in bulk host. We then propose how to take advantage of this enhancement to implement coherent quantum dot excitation by two-photon absorption, entangled photon pair generation by two-photon spontaneous emission, and single-photon generation at telecommunication wavelengths by two-photon stimulated and spontaneous emission.

  9. Formation of long-range ordered quantum dots arrays in amorphous matrix by ion beam irradiation

    SciTech Connect (OSTI)

    Buljan, M. [Charles University in Prague, Prague 12116 (Czech Republic); Ruder Boskovic Institute, Zagreb 10000 (Croatia); Bogdanovic-Radovic, I.; Karlusic, M.; Desnica, U. V.; Radic, N.; Dubcek, P. [Ruder Boskovic Institute, Zagreb 10000 (Croatia); Drazic, G. [Jozef Stefan Institute, Ljubljana 1000 (Slovenia); Salamon, K. [Institute of Physics, Zagreb 10000 (Croatia); Bernstorff, S. [Sincrotrone Trieste, Basovizza 34012 (Italy); Holy, V. [Charles University in Prague, Prague 12116 (Czech Republic)

    2009-08-10T23:59:59.000Z

    We demonstrate the production of a well ordered three-dimensional array of Ge quantum dots in amorphous silica matrix. The ordering is achieved by ion beam irradiation and annealing of a multilayer film. Structural analysis shows that quantum dots nucleate along the direction of the ion beam used for irradiation, while the mutual distance of the quantum dots is determined by the diffusion properties of the multilayer material rather than the distances between traces of ions that are used for irradiation.

  10. Features of the electronic spectrum in a type-I core - shell quantum dot

    SciTech Connect (OSTI)

    Igoshina, S E; Karmanov, A A [Penza State University, Penza (Russian Federation)

    2013-01-31T23:59:59.000Z

    The model is proposed, which allows one to solve the problem of finding the energy spectrum and the wave function of an electron in a type-I core - shell quantum dot. It is shown that the size of the core and shell can serve as control parameters for the optimisation of the energy structure of the quantum dot in order to obtain the real structures with desired electrophysical and optical properties. (quantum dots)

  11. Whispering gallery modes in quantum dot-embedded dielectric microspheres for tagless remote refractometric sensing

    E-Print Network [OSTI]

    Pang, Shuo

    2008-10-10T23:59:59.000Z

    S coating. The CdSe/Zns core/shell quantum dots are prepared colloidally via organometallic synthesis. In these experiments, green quantum dots with an emission peak at 530nm are used. The absorption and emission spectra are shown in Figure 9. 23... WHISPERING GALLERY MODES IN QUANTUM DOT-EMBEDDED DIELECTRIC MICROSPHERES FOR TAGLESS REMOTE REFRACTOMETRIC SENSING A Thesis by SHUO PANG Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment...

  12. Computational models for the berry phase in semiconductor quantum dots

    SciTech Connect (OSTI)

    Prabhakar, S., E-mail: rmelnik@wlu.ca; Melnik, R. V. N., E-mail: rmelnik@wlu.ca [M2NeT Lab, Wilfrid Laurier University, 75 University Ave W, Waterloo, ON N2L 3C5 (Canada); Sebetci, A. [Department of Mechanical Engineering, Mevlana University, 42003, Konya (Turkey)

    2014-10-06T23:59:59.000Z

    By developing a new model and its finite element implementation, we analyze the Berry phase low-dimensional semiconductor nanostructures, focusing on quantum dots (QDs). In particular, we solve the Schrödinger equation and investigate the evolution of the spin dynamics during the adiabatic transport of the QDs in the 2D plane along circular trajectory. Based on this study, we reveal that the Berry phase is highly sensitive to the Rashba and Dresselhaus spin-orbit lengths.

  13. Cavity Quantum Electrodynamics with a Single Quantum Dot Coupled to a Photonic Molecule

    E-Print Network [OSTI]

    Arka Majumdar; Armand Rundquist; Michal Bajcsy; Jelena Vu?kovi?

    2012-01-30T23:59:59.000Z

    We demonstrate the effects of cavity quantum electrodynamics for a quantum dot coupled to a photonic molecule, consisting of a pair of coupled photonic crystal cavities. We show anti-crossing between the quantum dot and the two super-modes of the photonic molecule, signifying achievement of the strong coupling regime. From the anti-crossing data, we estimate the contributions of both mode-coupling and intrinsic detuning to the total detuning between the super-modes. Finally, we also show signatures of off-resonant cavity-cavity interaction in the photonic molecule.

  14. Investigation of quantum confinement behavior of zinc sulphide quantum dots synthesized via various chemical methods

    SciTech Connect (OSTI)

    Jose, Meera, E-mail: gunasekaran@karunya.edu; Sakthivel, T., E-mail: gunasekaran@karunya.edu; Chandran, Hrisheekesh T., E-mail: gunasekaran@karunya.edu; Nivea, R., E-mail: gunasekaran@karunya.edu; Gunasekaran, V., E-mail: gunasekaran@karunya.edu [Nanomaterials Research Lab, Department of Nanoscience and Technology, Karunya University, Coimbatore - 641 114, Tamil Nadu (India)

    2014-10-15T23:59:59.000Z

    In this work, undoped and Ag-doped ZnS quantum dots were synthesized using various chemical methods. The products were characterized using X-ray diffraction (XRD), UV-visible spectroscopy and Photoluminescence spectroscopy. Our results revealed that the size of the as-prepared samples range from 1–6 nm in diameter and have a cubic zinc-blende structure. Also, we observed the emission of different wavelength of light from different sized quantum dots of the same material due to quantum confinement effect. The results will be presented in detail and ZnS can be a potential candidate for optical device development and applications.

  15. GaN/AlN Quantum Wells and Quantum Dots for Unipolar Devices at Telecommunication Wavelengths

    SciTech Connect (OSTI)

    Julien, Francois H.; Tchernycheva, Maria; Doyennette, Laetitia; Nevou, Laurent; Lupu, Anatole; Warde, Elias [Institut d'Electronique Fondamentale, Universite Paris Sud, UMR 8622 CNRS, 91405 Orsay (France); Guillot, Fabien; Monroy, Eva; Bellet-Amalric, Edith [Equipe mixte CEACNRS-UJF, DRFMC/SP2M/PSC, CEA Grenoble, 17 rue des Martyrs, 38054 Grenoble (France); Vardi, Alon; Bahir, Gad [Departement of Electrical Engineering, Technion-Israel Institute of Technology, Haifa 3200 (Israel)

    2007-04-10T23:59:59.000Z

    We report on the latest achievements in terms of growth and optical investigation of ultrathin GaN/AlN isolated and coupled quantum wells grown by plasma-assisted molecular-beam epitaxy. We also present the observation of intraband absorption in self-organized GaN quantum dots and on the application to infrared photodetection at telecommunication wavelengths.

  16. artificial quantum-dot helium: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  17. acid-capped cdse quantum-dot: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  18. Size and spatial homogeneity of SiGe quantum dots in amorphous silica matrix

    SciTech Connect (OSTI)

    Buljan, Maja [Faculty of Mathematics and Physics, Charles University in Prague, Prague 12116 (Czech Republic); Ruder Boskovic Institute, P.O. Box 180, 10002 Zagreb (Croatia); Pinto, Sara R. C.; Rolo, Anabela G.; Levichev, Sergey; Gomes, Maria J. M. [Physics Department, University of Minho, 4710-057 Braga (Portugal); Kashtiban, Reza J.; Bangert, Ursel [Nanostructured Materials Research Group, School of Materials, University of Manchester, P.O. Box 88, Manchester, M1 7HS (United Kingdom); Chahboun, Adil [Physics Department, University of Minho, 4710-057 Braga (Portugal); Department of Physics, Dhar Mehraz Sciences Faculty, BP 1796, Fes (Morocco); Holy, Vaclav [Faculty of Mathematics and Physics, Charles University in Prague, Prague 12116 (Czech Republic)

    2009-10-15T23:59:59.000Z

    In this paper, we present a study of structural properties of SiGe quantum dots formed in amorphous silica matrix by magnetron sputtering technique. We investigate deposition conditions leading to the formation of dense and uniformly sized quantum dots, distributed homogeneously in the matrix. X-ray and Raman spectroscopy were used to estimate the Si content. A detailed analysis based on grazing incidence small angle x-ray scattering revealed the influence of the deposition conditions on quantum dot sizes, size distributions, spatial arrangement, and concentration of quantum dots in the matrix, as well as the Si:Ge content.

  19. REVIEW ARTICLE Semiconductor quantum dot-sensitized

    E-Print Network [OSTI]

    Cao, Guozhong

    of low-cost and high-performance solar cells for sustainable energy sources to re- place fossil fuels has) fabrication methods of QDs, and 4) nanocrystalline photoelectrodes for solar cells. We also make suggestions band gap depending on the QD size, 2) a larger extinction coefficient, 3) higher stability toward water

  20. Resonant excitation and photon entanglement from semiconductor quantum dots

    E-Print Network [OSTI]

    Ana Predojevi?

    2015-03-01T23:59:59.000Z

    In this chapter we review the use of semiconductor quantum dots as sources of quantum light. Principally, we focus on resonant two-photon excitation, which is a method that allows for on-demand generation of photon pairs. We explore the advantages of resonant excitation and present a number of measurements that were made in this excitation regime. In particular, we cover the following topics: photon statistics, coherent manipulation of the ground-excited state superposition, and generation of time-bin entangled photon pairs.

  1. Highly uniform, multi-stacked InGaAs/GaAs quantum dots embedded in a GaAs nanowire

    SciTech Connect (OSTI)

    Tatebayashi, J., E-mail: tatebaya@iis.u-tokyo.ac.jp; Ota, Y. [NanoQUINE, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Ishida, S.; Nishioka, M.; Iwamoto, S.; Arakawa, Y. [NanoQUINE, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan); Institute of Industrial Science, The University of Tokyo, 4-6-1, Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

    2014-09-08T23:59:59.000Z

    We demonstrate a highly uniform, dense stack of In{sub 0.22}Ga{sub 0.78}As/GaAs quantum dot (QD) structures in a single GaAs nanowire (NW). The size (and hence emission energy) of individual QD is tuned by careful control of the growth conditions based on a diffusion model of morphological evolution of NWs and optical characterization. By carefully tailoring the emission energies of individual QD, dot-to-dot inhomogeneous broadening of QD stacks in a single NW can be as narrow as 9.3?meV. This method provides huge advantages over traditional QD stack using a strain-induced Stranski-Krastanow growth scheme. We show that it is possible to fabricate up to 200 uniform QDs in single GaAs NWs using this growth technique without degradation of the photoluminescence intensity.

  2. Epitaxial lift-off of quantum dot enhanced GaAs single junction solar cells

    SciTech Connect (OSTI)

    Bennett, Mitchell F.; Bittner, Zachary S.; Forbes, David V.; Hubbard, Seth M., E-mail: smhsps@rit.edu [Rochester Institute of Technology, Rochester, New York 14623 (United States); Rao Tatavarti, Sudersena; Wibowo, Andree; Pan, Noren; Chern, Kevin [MicroLink Devices, Inc., Niles, Illinois 60714 (United States)] [MicroLink Devices, Inc., Niles, Illinois 60714 (United States); Phillip Ahrenkiel, S. [South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 (United States)] [South Dakota School of Mines and Technology, Rapid City, South Dakota 57701 (United States)

    2013-11-18T23:59:59.000Z

    InAs/GaAs strain-balanced quantum dot (QD) n-i-p solar cells were fabricated by epitaxial lift-off (ELO), creating thin and flexible devices that exhibit an enhanced sub-GaAs bandgap current collection extending into the near infrared. Materials and optical analysis indicates that QD quality after ELO processing is preserved, which is supported by transmission electron microscopy images of the QD superlattice post-ELO. Spectral responsivity measurements depict a broadband resonant cavity enhancement past the GaAs bandedge, which is due to the thinning of the device. Integrated external quantum efficiency shows a QD contribution to the short circuit current density of 0.23?mA/cm{sup 2}.

  3. Manipulating surface diffusion and elastic interactions to obtain quantum dot multilayer arrangements over different length scales

    SciTech Connect (OSTI)

    Placidi, E., E-mail: ernesto.placidi@ism.cnr.it; Arciprete, F. [Istituto di Struttura della Materia, CNR, Via del Fosso del Cavaliere 100, 00133 Rome (Italy); Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Latini, V.; Latini, S.; Patella, F. [Università di Roma “Tor Vergata”, Dipartimento di Fisica, via della Ricerca Scientifica 1, 00133 Rome (Italy); Magri, R. [Dipartimento di Scienze Fisiche, Informatiche e Matematiche (FIM), Università di Modena e Reggio Emilia, and Centro S3 CNR-Istituto Nanoscienze, Via Campi 213/A, 4100 Modena (Italy); Scuderi, M.; Nicotra, G. [CNR-IMM, Strada VIII, 5, 95121 Catania (Italy)

    2014-09-15T23:59:59.000Z

    An innovative multilayer growth of InAs quantum dots on GaAs(100) is demonstrated to lead to self-aggregation of correlated quantum dot chains over mesoscopic distances. The fundamental idea is that at critical growth conditions is possible to drive the dot nucleation only at precise locations corresponding to the local minima of the Indium chemical potential. Differently from the known dot multilayers, where nucleation of new dots on top of the buried ones is driven by the surface strain originating from the dots below, here the spatial correlations and nucleation of additional dots are mostly dictated by a self-engineering of the surface occurring during the growth, close to the critical conditions for dot formation under the fixed oblique direction of the incoming As flux, that drives the In surface diffusion.

  4. Single photon absorption and dynamic control of a coupled quantum dot-cavity system

    E-Print Network [OSTI]

    Robert Johne; Andrea Fiore

    2011-10-11T23:59:59.000Z

    We theoretically investigate the dynamic interaction of a quantum dot in a nanocavity with timesymmetric single photon pulses. The simulations, based on a wavefunction approach, reveal that almost perfect single photon absorption occurs for quantum dot-cavity systems operating on the edge between strong and weak coupling regime. The computed maximum absorptions probability is close to unity for pulses with a typical length comparable to the half of the Rabi period. Furthermore, the dynamic control of the quantum dot energy via electric fields allows the freezing of the light-matter interaction leaving the quantum dot in its excited state. Shaping of single photon wavepackets by the electric field control is limited by the occurrence of chirping of the single photon pulse. This understanding of the interaction of single photon pulses with the quantum dot-cavity system provides the basis for the development of advanced protocols for quantum information processing in the solid state.

  5. Towards a feasible implementation of quantum neural networks using quantum dots

    E-Print Network [OSTI]

    M. V. Altaisky; N. N. Zolnikova; N. E. Kaputkina; V. A. Krylov; Yu. E. Lozovik; N. S. Dattani

    2015-03-17T23:59:59.000Z

    We propose an implementation of quantum neural networks using an array of single-electron quantum dots with dipole-dipole interactions. We demonstrate that this implementation is both feasible and versatile by studying it within the framework of GaAs based quantum dot qubits coupled to a reservoir of acoustic phonons; a system whose decoherence properties have been experimentally and theoretically characterized with meticulous detail, and is considered one of the most accurately understood open quantum systems. Using numerically exact Feynman integral calculations, we have found that the quantum coherence in our neural networks survive for several ns even at liquid nitrogen temperatures (77 K), which is three orders of magnitude higher than current implementations which are based on SQUIDs operating at temperatures in the mK range. Furthermore, the previous quantum dot based proposals required control via manipulating the phonon bath, which is extremely difficult in real experiments. An advantage of our implementation is that it can be easily controlled, since dipole-dipole interaction strengths can be changed via the spacing between the dots and applying external fields.

  6. Impact of nanostructure configuration on the photovoltaic performance of quantum dot arrays

    E-Print Network [OSTI]

    Berbezier, Aude

    2014-01-01T23:59:59.000Z

    In this work, an effective quantum model based on the non-equilibrium Green's function formalism is used to investigate a selectively contacted high density quantum dot array in an wide band gap host matrix for operation as a quantum dot-enhanced single junction solar cell. By establishing a direct relation between nanostructure configuration and optoelectronic properties, the investigation reveals the influence of inter-dot and dot-contact coupling strength on the radiative rates and consequently on the ultimate performance of photovoltaic devices with finite quantum dot arrays as the active medium. The dominant effects originate in the dependence of the Joint Density of States on the inter-dot coupling in terms of band width and effective band gap.

  7. Detecting quantum-coherent nanomechanical oscillations using the current-noise spectrum of a double quantum dot

    E-Print Network [OSTI]

    Neill Lambert; Franco Nori

    2008-12-17T23:59:59.000Z

    We consider a nanomechanical resonator coupled to a double quantum dot. We demonstrate how the finite-frequency current noise spectrum through the double quantum dot can be used to distinguish classical and quantum behaviour in the nearby nano-electromechanical resonator. We also show how the full frequency current noise spectrum gives important information on the combined double quantum dot-resonator energy spectrum. Finally, we point out regimes where the quantum state of the resonator becomes squeezed, and also examine the cross-correlated electron-phonon current noise.

  8. Physica E 32 (2006) 1416 Tuning the cross-gap transition energy of a quantum dot

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    2006-01-01T23:59:59.000Z

    ; Spectroscopy; Energy tuning Self-assembled semiconductor quantum dots (QDs) are of great interest for quantum resistance bridge circuit in combination with a lock in amplifier is used to measure the change in resistance

  9. Multispectral imaging via luminescent down-shifting with colloidal quantum dots

    E-Print Network [OSTI]

    Jaworski, Frank B.

    The high infrared quantum yield, continuous absorption spectrum, and band edge tunability of colloidal quantum dots (QD) has opened up new opportunities to use luminescent down shifting for multispectral imaging in the ...

  10. Title: Development of Plasmon Assisted Quantum DOT Sensors Multispectral and Polarization Selective Imaging

    E-Print Network [OSTI]

    Johnson, Eric E.

    Title: Development of Plasmon Assisted Quantum DOT Sensors for Multispectral and Polarization in plasmonic nanostructures. Spectral and polarization sensitive EO sensors provide unique remote sensing of subwavelength plasmon-polariton assisted quantum dot (QD) photodetectors (PDs) for pixel-level spectral

  11. Mid Infrared Focal Plane Arrays With Nanoscale Quantum Dots and Superlattices

    E-Print Network [OSTI]

    Krishna, Sanjay

    Mid Infrared Focal Plane Arrays With Nanoscale Quantum Dots and Superlattices S. Krishna Center- Molecular beam epitaxy, Nanoscale, Quantum Dots Superlattices, Antimonides, Mid-infrared photodetector. I. INTRODUCTION Presently, the state of the art photon detectors for the mid wave infrared (MWIR, 3-5 µm) and long

  12. Light extraction analysis and enhancement in a quantum dot light emitting diode

    E-Print Network [OSTI]

    Wu, Shin-Tson

    Light extraction analysis and enhancement in a quantum dot light emitting diode Ruidong Zhu outcoupling and angular performance of quantum dot light emitting diode (QLED). To illustrate the design principles, we use a red QLED as an example and compare its performance with an organic light emitting diode

  13. GeSi intermixing in Ge quantum dots on Si,,001... and Si,,111... F. Boscherinia)

    E-Print Network [OSTI]

    Ge­Si intermixing in Ge quantum dots on Si,,001... and Si,,111... F. Boscherinia) Laboratori December 1999 Exploiting Ge K-edge x-ray absorption spectroscopy we provide direct evidence of Si­Ge intermixing in self-organized strained and unstrained Ge quantum dots on Si, and provide a quantitative

  14. Rapid degradation of CdSe/ZnS colloidal quantum dots exposed to gamma irradiation

    E-Print Network [OSTI]

    New Mexico, University of

    Rapid degradation of CdSe/ZnS colloidal quantum dots exposed to gamma irradiation Nathan J. Withers are reported. Optical degradation is evaluated by tracking the dependence of photoluminescence intensity on irradiation dose. CdSe/ZnS quantum dots show poor radiation hardness, and severely degrade after less than 20

  15. Mechanism for thermoelectric figure-of-merit enhancement in regimented quantum dot superlattices

    E-Print Network [OSTI]

    Mechanism for thermoelectric figure-of-merit enhancement in regimented quantum dot superlattices propose a mechanism for enhancement of the thermoelectric figure-of-merit in regimented quantum dot, as a result, to the thermoelectric figure-of-merit enhancement. To maximize the improvement, one has to tune

  16. Evidence for formation of multi-quantum dots in hydrogenated graphene

    E-Print Network [OSTI]

    Chuang, Chiashain; Puddy, Reuben K; Connolly, Malcolm R; Lo, Shun-Tsung; Lin, Huang-De; Chen, Tse-Ming; Smith, Charles G; Liang, Chi-Te

    2012-08-16T23:59:59.000Z

    Abstract We report the experimental evidence for the formation of multi-quantum dots in a hydrogenated single-layer graphene flake. The existence of multi-quantum dots is supported by the low-temperature measurements on a field effect transistor...

  17. Review paper: Toward highly efficient quantum-dot-and dye-sensitized solar cells

    E-Print Network [OSTI]

    Park, Byungwoo

    Review paper: Toward highly efficient quantum-dot- and dye-sensitized solar cells Hongsik Choi Interface control Light harvesting Tandem solar cell a b s t r a c t Dye- and quantum-dot-sensitized solar technologies of silicon-based solar cells should be resolved [7]. Dye-sensitized solar cells (DSSCs) have been

  18. Characterization of a microwave frequency resonator via a nearby quantum dot

    E-Print Network [OSTI]

    Wallraff, Andreas

    and superconducting qubits. The study of the inter- action between the electromagnetic field of such a resonator of a hybrid system consisting of a microwave transmission-line resonator and a lateral quantum dot defined is studied by monitoring the electrical conductance through the quantum dot. The presence of a strong

  19. Ambient-Processed Colloidal Quantum Dot Solar Cells via Individual Pre-Encapsulation of Nanoparticles

    E-Print Network [OSTI]

    Ambient-Processed Colloidal Quantum Dot Solar Cells via Individual Pre-Encapsulation, 2010; E-mail: ted.sargent@utoronto.ca Solution-processed solar cells employing colloidal quantum dots-junction and tandem solar cells both rely on IR-band-gap semiconductors, there has been much recent emphasis

  20. Coupled electromechanical effects in wurtzite quantum dots with wetting layers in gate controlled electric fields: The multiband case

    E-Print Network [OSTI]

    Melnik, Roderick

    Coupled electromechanical effects in wurtzite quantum dots with wetting layers in gate controlled quantifies the electromechanical effects on the band structure of wurtzite quantum dots. c Systematic study on the band structure calculations of wurtzite AlN/GaN quantum dots with wetting layers (WLs). Based

  1. Water-soluble luminescent quantum dots and biomolecular conjugates thereof and related compositions and method of use

    DOE Patents [OSTI]

    Nie, Shuming (Bloomington, IN); Chan, Warren C. W. (Bloomington, IN); Emory, Steven R. (Los Alamos, NM)

    2002-01-01T23:59:59.000Z

    The present invention provides a water-soluble luminescent quantum dot, a biomolecular conjugate thereof and a composition comprising such a quantum dot or conjugate. Additionally, the present invention provides a method of obtaining a luminescent quantum dot, a method of making a biomolecular conjugate thereof, and methods of using a biomolecular conjugate for ultrasensitive nonisotopic detection in vitro and in vivo.

  2. Water-soluble luminescent quantum dots and biomolecular conjugates thereof and related compositions and methods of use

    DOE Patents [OSTI]

    Nie, Shuming; Chan, Warren C. W.; Emory, Stephen

    2007-03-20T23:59:59.000Z

    The present invention provides a water-soluble luminescent quantum dot, a biomolecular conjugate thereof and a composition comprising such a quantum dot or conjugate. Additionally, the present invention provides a method of obtaining a luminescent quantum dot, a method of making a biomolecular conjugate thereof, and methods of using a biomolecular conjugate for ultrasensitive nonisotopic detection in vitro and in vivo.

  3. Theory of dynamic nuclear polarization and feedback in quantum dots

    E-Print Network [OSTI]

    Sophia E. Economou; Edwin Barnes

    2014-04-06T23:59:59.000Z

    An electron confined in a quantum dot interacts with its local nuclear spin environment through the hyperfine contact interaction. This interaction combined with external control and relaxation or measurement of the electron spin allows for the generation of dynamic nuclear polarization. The quantum nature of the nuclear bath, along with the interplay of coherent external fields and incoherent dynamics in these systems renders a wealth of intriguing phenomena seen in recent experiments such as electron Zeeman frequency focusing, hysteresis, and line dragging. We develop in detail a fully quantum, self-consistent theory that can be applied to such experiments and that moreover has predictive power. Our theory uses the operator sum representation formalism in order to incorporate the incoherent dynamics caused by the additional, Markovian bath, which in self-assembled dots is the vacuum field responsible for electron-hole optical recombination. The beauty of this formalism is that it reduces the complexity of the problem by encoding the joint dynamics of the external coherent and incoherent driving in an effective dynamical map that only acts on the electron spin subspace. This together with the separation of timescales in the problem allows for a tractable and analytically solvable formalism. The key role of entanglement between the electron spin and the nuclear spins in the formation of dynamic nuclear polarization naturally follows from our solution. We demonstrate the theory in detail for an optical pulsed experiment and present an in-depth discussion and physical explanation of our results.

  4. Quantum Dots-based Reverse Phase Protein Microarray

    SciTech Connect (OSTI)

    Shingyoji, Masato; Gerion, Daniele; Pinkel, Dan; Gray, Joe W.; Chen, Fanqing

    2005-07-15T23:59:59.000Z

    CdSe nanocrystals, also called quantum dots (Qdots) are a novel class of fluorophores, which have a diameter of a few nanometers and possess high quantum yield, tunable emission wavelength and photostability. They are an attractive alternative to conventional fluorescent dyes. Quantum dots can be silanized to be soluble in aqueous solution under biological conditions, and thus be used in bio-detection. In this study, we established a novel Qdot-based technology platform that can perform accurate and reproducible quantification of protein concentration in a crude cell lysate background. Protein lysates have been spiked with a target protein, and a dilution series of the cell lysate with a dynamic range of three orders of magnitude has been used for this proof-of-concept study. The dilution series has been spotted in microarray format, and protein detection has been achieved with a sensitivity that is at least comparable to standard commercial assays, which are based on horseradish peroxidase (HRP) catalyzed diaminobenzidine (DAB) chromogenesis. The data obtained through the Qdot method has shown a close linear correlation between relative fluorescence unit and relative protein concentration. The Qdot results are in almost complete agreement with data we obtained with the well-established HRP-DAB colorimetric array (R{sup 2} = 0.986). This suggests that Qdots can be used for protein quantification in microarray format, using the platform presented here.

  5. Coupling of PbS Quantum Dots to Photonic Crystal Cavities at Room Temperature

    E-Print Network [OSTI]

    Ilya Fushman; Dirk Englund; Jelena Vuckovic

    2005-05-14T23:59:59.000Z

    We demonstrate the coupling of PbS quantum dot emission to photonic crystal cavities at room temperature. The cavities are defined in 33% Al, AlGaAs membranes on top of oxidized AlAs. Quantum dots were dissolved in Poly-methyl-methacrylate (PMMA) and spun on top of the cavities. Quantum dot emission is shown to map out the structure resonances, and may prove to be viable sources for room temperature cavity coupled single photon generation for quantum information processing applications. These results also indicate that such commercially available quantum dots can be used for passive structure characterization. The deposition technique is versatile and allows layers with different dot densities and emission wavelengths to be re-deposited on the same chip.

  6. Intermediate-band photosensitive device with quantum dots embedded in energy fence barrier

    DOE Patents [OSTI]

    Forrest, Stephen R. (Ann Arbor, MI); Wei, Guodan (Ann Arbor, MI)

    2010-07-06T23:59:59.000Z

    A plurality of layers of a first semiconductor material and a plurality of dots-in-a-fence barriers disposed in a stack between a first electrode and a second electrode. Each dots-in-a-fence barrier consists essentially of a plurality of quantum dots of a second semiconductor material embedded between and in direct contact with two layers of a third semiconductor material. Wave functions of the quantum dots overlap as at least one intermediate band. The layers of the third semiconductor material are arranged as tunneling barriers to require a first electron and/or a first hole in a layer of the first material to perform quantum mechanical tunneling to reach the second material within a respective quantum dot, and to require a second electron and/or a second hole in a layer of the first semiconductor material to perform quantum mechanical tunneling to reach another layer of the first semiconductor material.

  7. Computational modeling of electrophotonics nanomaterials: Tunneling in double quantum dots

    SciTech Connect (OSTI)

    Vlahovic, Branislav, E-mail: vlahovic@nccu.edu; Filikhin, Igor, E-mail: vlahovic@nccu.edu [Department of Physics, North Carolina Central University, 1801 Fayetteville Street, Durham, North Carolina 27707 (United States)

    2014-10-06T23:59:59.000Z

    Single electron localization and tunneling in double quantum dots (DQD) and rings (DQR) and in particular the localized-delocalized states and their spectral distributions are considered in dependence on the geometry of the DQDs (DQRs). The effect of violation of symmetry of DQDs geometry on the tunneling is studied in details. The cases of regular and chaotic geometries are considered. It will be shown that a small violation of symmetry drastically affects localization of electron and that anti-crossing of the levels is the mechanism of tunneling between the localized and delocalized states in DQRs.

  8. Photocurrent extraction efficiency in colloidal quantum dot photovoltaics

    SciTech Connect (OSTI)

    Kemp, K. W.; Wong, C. T. O.; Hoogland, S. H.; Sargent, E. H. [Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4 (Canada)] [Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4 (Canada)

    2013-11-18T23:59:59.000Z

    The efficiency of photocurrent extraction was studied directly inside operating Colloidal Quantum Dot (CQD) photovoltaic devices. A model was derived from first principles for a thin film p-n junction with a linearly spatially dependent electric field. Using this model, we were able to clarify the origins of recent improvement in CQD solar cell performance. From current-voltage diode characteristics under 1 sun conditions, we extracted transport lengths ranging from 39 nm to 86 nm for these materials. Characterization of the intensity dependence of photocurrent extraction revealed that the dominant loss mechanism limiting the transport length is trap-mediated recombination.

  9. Photoluminescence-enhanced biocompatible quantum dots by phospholipid functionalization

    SciTech Connect (OSTI)

    Shi Yunfeng [School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China); He Peng [Department of Chemistry, North Carolina State University, Raleigh, NC 27695 (United States)], E-mail: phe@ncsu.edu; Zhu Xinyuan [School of Chemistry and Chemical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Shanghai 200240 (China); Instrumental Analysis Center, Shanghai Jiao Tong University, 1954 Huashan Road, Shanghai 200030 (China)], E-mail: xyzhu@sjtu.edu.cn

    2008-10-02T23:59:59.000Z

    A simple two-step strategy using phospholipid (PPL) to functionalize core/shell CdSe/ZnS quantum dots (QDs) has been described. The experimental data show that the use of S-H terminated PPL results not only in the high colloidal stability of core/shell CdSe/ZnS QDs in the aqueous phase, but also in the significant enhancement of photoluminescence. The degree of the enhancement is a function of the PPL-CdSe/ZnS QDs sample concentration. These results might be promising for future biological platform in new devices ranging from photovoltaic cells to biosensors and other devices.

  10. Nanoscale engineering boosts performance of quantum dot light emitting

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645U.S. DOE Office of Science (SC)Integrated CodesTransparency VisitSilver Toyota PriusNSRdiodes Quantum dot light

  11. Activation of molecular catalysts using semiconductor quantum dots

    DOE Patents [OSTI]

    Meyer, Thomas J. (Chapel Hill, NC); Sykora, Milan (Los Alamos, NM); Klimov, Victor I. (Los Alamos, NM)

    2011-10-04T23:59:59.000Z

    Photocatalytic materials based on coupling of semiconductor nanocrystalline quantum dots (NQD) and molecular catalysts. These materials have capability to drive or catalyze non-spontaneous chemical reactions in the presence of visible radiation, ultraviolet radiation, or both. The NQD functions in these materials as a light absorber and charge generator. Following light absorption, the NQD activates a molecular catalyst adsorbed on the surface of the NQD via transfer of one or more charges (either electrons or electron-holes) from the NQD to the molecular catalyst. The activated molecular catalyst can then drive a chemical reaction. A photoelectrolytic device that includes such photocatalytic materials is also described.

  12. Shiny quantum dots brighten future of solar cells

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645U.S. DOE Office of ScienceandMesa del Sol HomeFacebookScholarship Fund scholarshipsShedding LightShiny quantum dots

  13. Sandia Energy - InAs Quantum Dot Transitions

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645U.S. DOE Office of Scienceand RequirementsCoatingsUltra-High-VoltagePower Company'sInAs Quantum Dot Transitions Home

  14. Theory of Electro-optic Modulation via a Quantum Dot Coupled to a Nano-resonator

    E-Print Network [OSTI]

    Arka Majumdar; Nicolas Manquest; Andrei Faraon; Jelena Vuckovic

    2009-11-27T23:59:59.000Z

    In this paper, we analyze the performance of an electro-optic modulator based on a single quantum dot strongly coupled to a nano-resonator, where electrical control of the quantum dot frequency is achieved via quantum confined Stark effect. Using realistic system parameters, we show that modulation speeds of a few tens of GHz are achievable with this system, while the energy per switching operation can be as small as 0.5 fJ. In addition, we study the non-linear distortion, and the effect of pure quantum dot dephasing on the performance of the modulator.

  15. High Efficiency Colloidal Quantum Dot Phosphors

    SciTech Connect (OSTI)

    Kahen, Keith

    2013-12-31T23:59:59.000Z

    The project showed that non-Cd containing, InP-based nanocrystals (semiconductor materials with dimensions of ~6 nm) have high potential for enabling next-generation, nanocrystal-based, on chip phosphors for solid state lighting. Typical nanocrystals fall short of the requirements for on chip phosphors due to their loss of quantum efficiency under the operating conditions of LEDs, such as, high temperature (up to 150 °C) and high optical flux (up to 200 W/cm2). The InP-based nanocrystals invented during this project maintain high quantum efficiency (>80%) in polymer-based films under these operating conditions for emission wavelengths ranging from ~530 to 620 nm. These nanocrystals also show other desirable attributes, such as, lack of blinking (a common problem with nanocrystals which limits their performance) and no increase in the emission spectral width from room to 150 °C (emitters with narrower spectral widths enable higher efficiency LEDs). Prior to these nanocrystals, no nanocrystal system (regardless of nanocrystal type) showed this collection of properties; in fact, other nanocrystal systems are typically limited to showing only one desirable trait (such as high temperature stability) but being deficient in other properties (such as high flux stability). The project showed that one can reproducibly obtain these properties by generating a novel compositional structure inside of the nanomaterials; in addition, the project formulated an initial theoretical framework linking the compositional structure to the list of high performance optical properties. Over the course of the project, the synthetic methodology for producing the novel composition was evolved to enable the synthesis of these nanomaterials at a cost approximately equal to that required for forming typical conventional nanocrystals. Given the above results, the last major remaining step prior to scale up of the nanomaterials is to limit the oxidation of these materials during the tens of thousands of hours of LED operation. Once the LED phosphor lifetime specifications are met, these nanocrystals will enable white LEDs for solid state lighting to simultaneously have increased efficiency and improved light quality, in addition to enabling the creation of custom light spectrums. These improvements to white LEDs will help accelerate the adoption of SSL, leading to large savings in US and worldwide energy costs.

  16. Energy spectra of two electrons in a circular quantum dot

    E-Print Network [OSTI]

    Anjana Sinha; Y. P. Varshni

    2002-08-27T23:59:59.000Z

    The electron interaction energy of two interacting electrons in a circular quantum dot (with hard wall confinement) is investigated in the framework of the semi-classical Wentzel-Kramers-Brillouin (WKB) approximation. The two electrons are assumed to be in an infinitely deep well of radius $r_0$, in a simple configuration with one electron fixed at the origin. The corresponding Schrodinger equation, with hard wall boundary conditions, is also solved exactly by numerical integration. It is observed that the agreement between the two energy values is quite good, suggesting that the WKB approximation works well for such a confined quantum system as well. This may provide motivation to extend this to more realistic confined potentials.

  17. Volmer-Weber Growth of Nanoscale Self-Assembled Quantum Dots

    SciTech Connect (OSTI)

    Huang, Rui

    2009-08-15T23:59:59.000Z

    Our research has focused on the fundamental understanding of the physical mechanisms and experimental methodologies to probe various growth conditions, their effects on density, size uniformity, and spatial organization of self-assembled quantum dots (SAQDs). Theoretical models and numerical simulations have been developed to understand the nonlinear dynamics of surface pattern evolution and self assembly processes. Fabrication processes of semiconductor and metal SAQDs on high-k dielectrics have been developed, which have enabled the technology development of high-speed, low-power nonvolatile memory devices for nanoelectronics applications. Over the four years of the project, six graduate students have been trained in this research project, and four of them have graduated with PhD degrees. Our research has been reported in 11 journal articles. Both PIs and their students have given numerous presentations at national/international conferences as well as invited seminars. A list of publications and presentations is attached to the end of this report.

  18. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect (OSTI)

    Pinto, S. R. C.; Ramos, M. M. D.; Gomes, M. J. M. [University of Minho, Centre of Physics and Physics Department, Braga 4710-057 (Portugal); Buljan, M. [Ruder Boskovic Institute, Bijenicka cesta 54, Zagreb 10000 (Croatia); Chahboun, A. [University of Minho, Centre of Physics and Physics Department, Braga 4710-057 (Portugal); Physics Department, FST Tanger, Tanger BP 416 (Morocco); Roldan, M. A.; Molina, S. I. [Departamento de Ciencia de los Materiales e Ing. Metalurgica y Q. I., Universidad de Cadiz, Cadiz (Spain); Bernstorff, S. [Sincrotrone Trieste, SS 14 km163, 5, Basovizza 34012 (Italy); Varela, M.; Pennycook, S. J. [Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Barradas, N. P.; Alves, E. [Instituto Superior Tecnico e Instituto Tecnologico e Nuclear-, EN10, Sacavem 2686-953 (Portugal)

    2012-04-01T23:59:59.000Z

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  19. Tuning the properties of Ge-quantum dots superlattices in amorphous silica matrix through deposition conditions

    SciTech Connect (OSTI)

    Pinto, S. [University of Minho, Portugal; Roldan Gutierrez, Manuel A [ORNL; Ramos, M. M.D. [University of Minho, Portugal; Gomes, M.J.M. [University of Minho, Portugal; Molina, S. I. [Universidad de Cadiz, Spain; Pennycook, Stephen J [ORNL; Varela del Arco, Maria [ORNL; Buljan, M. [R. Boskovic Institute, Zagreb, Croatia; Barradas, N. [Instituto Tecnologico e Nuclear (ITN), Lisbon, Portugal; Alves, E. [Instituto Tecnologico e Nuclear (ITN), Lisbon, Portugal; Chahboun, A. [FST Tanger, Morocco; Bernstorff, S. [Sincrotrone Trieste, Basovizza, Italy

    2012-01-01T23:59:59.000Z

    In this work, we investigate the structural properties of Ge quantum dot lattices in amorphous silica matrix, prepared by low-temperature magnetron sputtering deposition of (Ge+SiO{sub 2})/SiO{sub 2} multilayers. The dependence of quantum dot shape, size, separation, and arrangement type on the Ge-rich (Ge + SiO{sub 2}) layer thickness is studied. We show that the quantum dots are elongated along the growth direction, perpendicular to the multilayer surface. The size of the quantum dots and their separation along the growth direction can be tuned by changing the Ge-rich layer thickness. The average value of the quantum dots size along the lateral (in-plane) direction along with their lateral separation is not affected by the thickness of the Ge-rich layer. However, the thickness of the Ge-rich layer significantly affects the quantum dot ordering. In addition, we investigate the dependence of the multilayer average atomic composition and also the quantum dot crystalline quality on the deposition parameters.

  20. Green synthesis of highly efficient CdSe quantum dots for quantum-dots-sensitized solar cells

    SciTech Connect (OSTI)

    Gao, Bing; Shen, Chao; Zhang, Mengya; Yuan, Shuanglong; Yang, Yunxia, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn; Chen, Guorong, E-mail: yangyunxia@ecust.edu.cn, E-mail: grchen@ecust.edu.cn [Key Laboratory for Ultrafine Materials of Ministry of Education, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 (China); Zhang, Bo [Department of Physics, East China University of Science and Technology, Shanghai 200237 (China)

    2014-05-21T23:59:59.000Z

    Green synthesis of CdSe quantum dots for application in the quantum-dots-sensitized solar cells (QDSCs) is investigated in this work. The CdSe QDs were prepared with glycerol as the solvent, with sharp emission peak, full width at half maximum around 30?nm, and absorption peak from 475?nm to 510?nm. The reaction is environmental friendly and energy saving. What's more, the green synthesized CdSe QDs are coherence to the maximum remittance region of the solar spectrum and suitable as sensitizers to assemble onto TiO{sub 2} electrodes for cell devices application. What's more, the dynamic procedure of the carriers' excitation, transportation, and recombination in the QDSCs are discussed. Because the recombination of the electrons from the conduction band of TiO{sub 2}'s to the electrolyte affects the efficiency of the solar cells greatly, 3-Mercaptopropionic acid capped water-dispersible QDs were used to cover the surface of TiO{sub 2}. The resulting green synthesized CdSe QDSCs with Cu{sub 2}S as the electrode show a photovoltaic performance with a conversion efficiency of 3.39%.

  1. Real-time effective-action approach to the Anderson quantum dot

    E-Print Network [OSTI]

    Sexty, Denes; Pawlowski, Jan

    2010-01-01T23:59:59.000Z

    The non-equilibrium time evolution of an Anderson quantum dot is investigated. The quantum dot is coupled between two leads forming a chemical-potential gradient. We use Kadanoff-Baym dynamic equations within a non-perturbative resummation of the s-channel bubble chains. The effect of the resummation leads to the introduction of a frequency-dependent 4-point vertex. The tunneling to the leads is taken into account exactly. The method allows the determination of the transient as well as stationary transport through the quantum dot, and results are compared with different schemes discussed in the literature (fRG, ISPI, tDMRG and QMC).

  2. Real-time effective-action approach to the Anderson quantum dot

    E-Print Network [OSTI]

    Denes Sexty; Thomas Gasenzer; Jan Pawlowski

    2010-12-20T23:59:59.000Z

    The non-equilibrium time evolution of an Anderson quantum dot is investigated. The quantum dot is coupled between two leads forming a chemical-potential gradient. We use Kadanoff-Baym dynamic equations within a non-perturbative resummation of the s-channel bubble chains. The effect of the resummation leads to the introduction of a frequency-dependent 4-point vertex. The tunneling to the leads is taken into account exactly. The method allows the determination of the transient as well as stationary transport through the quantum dot, and results are compared with different schemes discussed in the literature (fRG, ISPI, tDMRG and QMC).

  3. Phonon-mediated coupling between quantum dots through an off-resonant microcavity

    E-Print Network [OSTI]

    Arka Majumdar; Michal Bajcsy; Armand Rundquist; Erik Kim; Jelena Vuckovic

    2011-11-30T23:59:59.000Z

    We present experimental results showing phonon-mediated coupling between two quantum dots embedded inside a photonic crystal microcavity. With only one of the dots being spectrally close to the cavity, we observe both frequency up-conversion and down-conversion of the pump light via a $\\sim1.2$ THz phonon. We demonstrate this process for both weak and strong regimes of dot-cavity coupling, and provide a simple theoretical model explaining our observations.

  4. Room-temperature lasing in microring cavities with an InAs/InGaAs quantum-dot active region

    SciTech Connect (OSTI)

    Kryzhanovskaya, N. V., E-mail: kryj@mail.ioffe.ru; Zhukov, A. E.; Nadtochy, A. M. [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation)] [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation); Maximov, M. V. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Moiseev, E. I. [St. Petersburg Polytechnic University (Russian Federation)] [St. Petersburg Polytechnic University (Russian Federation); Kulagina, M. M. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Savelev, A. V.; Arakcheeva, E. M. [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation)] [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation); Lipovskii, A. A. [St. Petersburg Polytechnic University (Russian Federation)] [St. Petersburg Polytechnic University (Russian Federation); Zubov, F. I. [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation)] [Russian Academy of Sciences, St. Petersburg Academic University, Nanotechnology Center for Research and Education (Russian Federation); Kapsalis, A.; Mesaritakis, C.; Syvridis, D. [University of Athens (Greece)] [University of Athens (Greece); Mintairov, A. [University of Notre Dame (United States)] [University of Notre Dame (United States); Livshits, D. [Innolume GmbH (Germany)] [Innolume GmbH (Germany)

    2013-10-15T23:59:59.000Z

    Microring cavities (diameter D = 2.7-7 {mu}m) with an active region based on InAs/InGaAs quantum dots are fabricated and their characteristics are studied by the microphotoluminescence method and near-field optical microscopy. A value of 22 000 is obtained for the Q factor of a microring cavity with the diameter D = 6 {mu}m. Lasing up to room temperature is obtained in an optically pumped ring microlaser with a diameter of D = 2.7 {mu}m.

  5. Engineering of quantum dot photon sources via electro-elastic fields

    E-Print Network [OSTI]

    Rinaldo Trotta; Armando Rastelli

    2015-03-01T23:59:59.000Z

    The possibility to generate and manipulate non-classical light using the tools of mature semiconductor technology carries great promise for the implementation of quantum communication science. This is indeed one of the main driving forces behind ongoing research on the study of semiconductor quantum dots. Often referred to as artificial atoms, quantum dots can generate single and entangled photons on demand and, unlike their natural counterpart, can be easily integrated into well-established optoelectronic devices. However, the inherent random nature of the quantum dot growth processes results in a lack of control of their emission properties. This represents a major roadblock towards the exploitation of these quantum emitters in the foreseen applications. This chapter describes a novel class of quantum dot devices that uses the combined action of strain and electric fields to reshape the emission properties of single quantum dots. The resulting electro-elastic fields allow for control of emission and binding energies, charge states, and energy level splittings and are suitable to correct for the quantum dot structural asymmetries that usually prevent these semiconductor nanostructures from emitting polarization-entangled photons. Key experiments in this field are presented and future directions are discussed.

  6. Distinctive Signature of Indium Gallium Nitride Quantum Dot Lasing in Microdisks Cavities

    E-Print Network [OSTI]

    Woolf, Alexander; Aharanovich, Igor; Zhu, Tongtong; Niu, Nan; Wang, Danqing; Oliver, Rachel A; Hu, Evelyn L

    2014-01-01T23:59:59.000Z

    Low threshold lasers realized within compact, high quality optical cavities enable a variety of nanophotonics applications. Gallium nitride (GaN) materials containing indium gallium nitride (InGaN) quantum dots and quantum wells offer an outstanding platform to study light matter interactions and realize practical devices such as efficient light emitting diodes and nanolasers. Despite progress in the growth and characterization of InGaN quantum dots, their advantages as the gain medium in low threshold lasers have not been clearly demonstrated. This work seeks to better understand the reasons for these limitations by focusing on the simpler, limited-mode microdisk cavities, and by carrying out comparisons of lasing dynamics in those cavities using varying gain media including InGaN quantum wells, fragmented quantum wells, and a combination of fragmented quantum wells with quantum dots. For each gain medium, we utilize the distinctive, high quality (Q~5500) modes of the cavities, and the change in the highest ...

  7. Enlarged symmetry and coherence in arrays of quantum dots A. V. Onufriev and J. B. Marston

    E-Print Network [OSTI]

    Onufriev, Alexey

    . A Hubbard model then describes a pillar array of coupled dots, and at half-filling the system can be mapped materials. Recent advances in nanofabrication tech- niques offer the possibility of constructing artificial- teractions that lift the degeneracy. However, as Stafford and Das Sarma noticed,3 semiconducting quantum dots

  8. High performance tunnel injection quantum dot comb laser

    SciTech Connect (OSTI)

    Lee, C.-S.; Guo Wei; Basu, Debashish; Bhattacharya, Pallab [Department of Electrical Engineering and Computer Science, Solid State Electronics Laboratory, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)

    2010-03-08T23:59:59.000Z

    A high-speed multiwavelength quantum dot comb laser, grown by molecular beam epitaxy, is demonstrated. The device is characterized with a 75.9 nm (full width at half maximum) and a 91.4 nm (DELTA{sub -15dB}) wide lasing spectrum. There are 105 and 185 simultaneously emitted longitudinal modes with a maximum channel intensity nonuniformity of less than 3 dB in the spectral range of 1231-1252 nm and 1274-1311 nm, respectively, for a laser with 1040 mum cavity length. The channel spacing can be tuned with cavity length and remains invariant in the temperature range of 300-323 K. The small signal modulation bandwidth is 7.5 GHz.

  9. Valley pair qubits in double quantum dots of gapped graphene

    E-Print Network [OSTI]

    G. Y. Wu; N. -Y. Lue; L. Chang

    2011-07-03T23:59:59.000Z

    The rise of graphene opens a new door to qubit implementation, as discussed in the recent proposal of valley pair qubits in double quantum dots of gapped graphene (Wu et al., arXiv: 1104.0443 [cond-mat.mes-hall]). The work here presents the comprehensive theory underlying the proposal. It discusses the interaction of electrons with external magnetic and electric fields in such structures. Specifically, it examines a strong, unique mechanism, i.e., the analogue of the 1st-order relativistic effect in gapped graphene. This mechanism is state mixing free and allows, together with the electrically tunable exchange coupling, a fast, all-electric manipulation of qubits via electric gates, in the time scale of ns. The work also looks into the issue of fault tolerance in a typical case, yielding at 10oK a long qubit coherence time (~O(ms)).

  10. Fluorescence quenching of CdSe quantum dots on graphene

    SciTech Connect (OSTI)

    Guo, Xi Tao; Hua Ni, Zhen, E-mail: zhni@seu.edu.cn; Yan Nan, Hai; Hui Wang, Wen [Department of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 211189 (China)] [Department of Physics and Key Laboratory of MEMS of the Ministry of Education, Southeast University, Nanjing 211189 (China); Yan Liao, Chun [Physics Department, National Photoelectric Technology and Functional Materials and Application of Science and Technology International Cooperation Base, Northwest University, Xi'an 710069 (China)] [Physics Department, National Photoelectric Technology and Functional Materials and Application of Science and Technology International Cooperation Base, Northwest University, Xi'an 710069 (China); Zhang, Yan; Wei Zhao, Wei [Jiangsu Key Laboratory for Design and Fabrication of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189 (China)] [Jiangsu Key Laboratory for Design and Fabrication of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189 (China)

    2013-11-11T23:59:59.000Z

    We studied systematically the fluorescence quenching of CdSe quantum dots (QDs) on graphene and its multilayers, as well as graphene oxide (GO) and reduced graphene oxide (rGO). Raman intensity of QDs was used as a quantitatively measurement of its concentration in order to achieve a reliable quenching factor (QF). It was found that the QF of graphene (?13.1) and its multilayers is much larger than rGO (?4.4), while GO (?1.5) has the lowest quenching efficiency, which suggests that the graphitic structure is an important factor for quenching the fluorescence of QDs. It was also revealed that the QF of graphene is not strongly dependent on its thicknesses.

  11. Gate-Tunable Graphene Quantum Dot and Dirac Oscillator

    E-Print Network [OSTI]

    Abdelhadi Belouad; Ahmed Jellal; Youness Zahidi

    2015-05-29T23:59:59.000Z

    We obtain the solution of the Dirac equation in (2+1) dimensions in the presence of a constant magnetic field normal to the plane together with a two-dimensional Dirac-oscillator potential coupling. We study the energy spectrum of graphene quantum dot (QD) defined by electrostatic gates. We give discussions of our results based on different physical settings, whether the cyclotron frequency is similar or larger/smaller compared to the oscillator frequency. This defines an effective magnetic field that produces the effective quantized Landau levels. We study analytically such field in gate-tunable graphene QD and show that our structure allow us to control the valley degeneracy. Finally, we compare our results with already published work and also discuss the possible applications of such QD.

  12. Gate-Tunable Graphene Quantum Dot and Dirac Oscillator

    E-Print Network [OSTI]

    Belouad, Abdelhadi; Zahidi, Youness

    2015-01-01T23:59:59.000Z

    We obtain the solution of the Dirac equation in (2+1) dimensions in the presence of a constant magnetic field normal to the plane together with a two-dimensional Dirac-oscillator potential coupling. We study the energy spectrum of graphene quantum dot (QD) defined by electrostatic gates. We give discussions of our results based on different physical settings, whether the cyclotron frequency is similar or larger/smaller compared to the oscillator frequency. This defines an effective magnetic field that produces the effective quantized Landau levels. We study analytically such field in gate-tunable graphene QD and show that our structure allow us to control the valley degeneracy. Finally, we compare our results with already published work and also discuss the possible applications of such QD.

  13. A comparison between semi-spheroid- and dome-shaped quantum dots coupled to wetting layer

    SciTech Connect (OSTI)

    Shahzadeh, Mohammadreza; Sabaeian, Mohammad, E-mail: Sabaeian@scu.ac.ir [Physics Department, Faculty of Science, Shahid Chamran University of Ahvaz, Ahvaz, 61357-43135 (Iran, Islamic Republic of)

    2014-06-15T23:59:59.000Z

    During the epitaxial growth method, self-assembled semi-spheroid-shaped quantum dots (QDs) are formed on the wetting layer (WL). However for sake of simplicity, researchers sometimes assume semi-spheroid-shaped QDs to be dome-shaped (hemisphere). In this work, a detailed and comprehensive study on the difference between electronic and transition properties of dome- and semi-spheroid-shaped quantum dots is presented. We will explain why the P-to-S intersubband transition behaves the way it does. The calculated results for intersubband P-to-S transition properties of quantum dots show two different trends for dome-shaped and semi-spheroid-shaped quantum dots. The results are interpreted using the probability of finding electron inside the dome/spheroid region, with emphasis on the effects of wetting layer. It is shown that dome-shaped and semi-spheroid-shaped quantum dots feature different electronic and transition properties, arising from the difference in lateral dimensions between dome- and semi-spheroid-shaped QDs. Moreover, an analogy is presented between the bound S-states in the quantum dots and a simple 3D quantum mechanical particle in a box, and effective sizes are calculated. The results of this work will benefit researchers to present more realistic models of coupled QD/WL systems and explain their properties more precisely.

  14. Luminescent, quantum dot-based anti-reflective coatings for crystalline silicon photovoltaics

    E-Print Network [OSTI]

    Bruer, Garrett (Garrett A.)

    2010-01-01T23:59:59.000Z

    This thesis demonstrates and evaluates the potential application of luminescent quantum dot/polymer solutions on crystalline silicon photovoltaics. After spin coating the QD/polymer onto silicon photodiodes, an increase ...

  15. Optimization of a microwave resonator cavity to perform electron spin resonance measurements on quantum dots

    E-Print Network [OSTI]

    Burger, Anat

    2006-01-01T23:59:59.000Z

    This thesis attempts to improve on an ongoing experiment of detecting electron spin resonance (ESR) on AlGaAs/GaAs lateral quantum dots. The experiment is performed in a 2.5 Tesla magnetic field at temperatures around ...

  16. Efficiency loss mechanisms in colloidal quantum-dot light-emitting diodes

    E-Print Network [OSTI]

    Shirasaki, Yasuhiro

    2013-01-01T23:59:59.000Z

    Saturated and tunable emission colors make colloidal quantum-dot light-emitting diodes (QD-LEDs) interesting for the next generation of display and lighting technologies. However, there still remain various hurdles to the ...

  17. The physics and chemistry of transport in CdSe quantum dot solids

    E-Print Network [OSTI]

    Jarosz, Mirna, 1981-

    2004-01-01T23:59:59.000Z

    Semiconductor quantum dots (QDs) have tunable opto-electronic properties and can be chemically synthesized and manipulated with ease, making them a promising novel material for many diverse applications. An understanding ...

  18. Exchange Control of Nuclear Spin Diffusion in a Double Quantum Dot

    E-Print Network [OSTI]

    Reilly, D. J.

    The influence of gate-controlled two-electron exchange on the relaxation of nuclear polarization in small ensembles (N?10[superscript 6]) of nuclear spins is examined in a GaAs double quantum dot system. Waiting in the ...

  19. Electrical excitation of colloidally synthesized quantum dots in metal oxide structures

    E-Print Network [OSTI]

    Wood, Vanessa Claire

    2010-01-01T23:59:59.000Z

    This thesis develops methods for integrating colloidally synthesized quantum dots (QDs) and metal oxides in optoelectronic devices, presents three distinct light emitting devices (LEDs) with metal oxides surrounding a QD ...

  20. Nuclear spin dynamics in double quantum dots: Fixed points, transients, and intermittency

    E-Print Network [OSTI]

    Rudner, M. S.

    Transport through spin-blockaded quantum dots provides a means for electrical control and detection of nuclear spin dynamics in the host material. Although such experiments have become increasingly popular in recent years, ...

  1. Lateral heterojunction photodetector consisting of molecular organic and colloidal quantum dot thin films

    E-Print Network [OSTI]

    exception being the dye- sensitized solar cell.3 Owing to its unique geometry, the present device also and that is sensitized across visible wavelengths by a thin film of colloidal CdSe nanocrystal quantum dots QDs . High

  2. Gain dynamics of quantum dot devices for dual-state operation

    SciTech Connect (OSTI)

    Kaptan, Y., E-mail: yuecel.kaptan@physik.tu-berlin.de; Herzog, B.; Kolarczik, M.; Owschimikow, N.; Woggon, U. [Institut für Optik und Atomare Physik, Technische Universität Berlin, Berlin (Germany); Schmeckebier, H.; Arsenijevi?, D.; Bimberg, D. [Institut für Festkörperphysik, Technische Universität Berlin, Berlin (Germany); Mikhelashvili, V.; Eisenstein, G. [Technion Institute of Technology, Faculty of Electrical Engineering, Haifa (Israel)

    2014-06-30T23:59:59.000Z

    Ground state gain dynamics of In(Ga)As-quantum dot excited state lasers are investigated via single-color ultrafast pump-probe spectroscopy below and above lasing threshold. Two-color pump-probe experiments are used to localize lasing and non-lasing quantum dots within the inhomogeneously broadened ground state. Single-color results yield similar gain recovery rates of the ground state for lasing and non-lasing quantum dots decreasing from 6 ps to 2 ps with increasing injection current. We find that ground state gain dynamics are influenced solely by the injection current and unaffected by laser operation of the excited state. This independence is promising for dual-state operation schemes in quantum dot based optoelectronic devices.

  3. InGaAs Quantum Dots Coupled to a Reservoir of Nonequilibrium Free Carriers

    E-Print Network [OSTI]

    Laemmlin, Matthias

    We discuss the impact of a 2D-charged carrier reservoir for high-speed optical amplification and modulated lasing in quantum dot (QD)-based devices by testing the amplification of short trains of high power, femtosecond ...

  4. Solar Hydrogen Production Using Carbon Quantum Dots and a Molecular Nickel Catalyst

    E-Print Network [OSTI]

    Martindale, Benjamin C. M.; Hutton, Georgina A. M.; Caputo, Christine A.; Reisner, Erwin

    2015-04-13T23:59:59.000Z

    Solar Hydrogen Production Using Carbon Quantum Dots and a Molecular Nickel Catalyst Benjamin C. M. Martindale,† Georgina A. M. Hutton,† Christine A. Caputo, and Erwin Reisner* Christian Doppler Laboratory for Sustainable SynGas Chemistry, Department...

  5. Narrow-Band Absorption-Enhanced Quantum Dot/J-Aggregate Conjugates

    E-Print Network [OSTI]

    Walker, Brian J.

    We report narrow-band absorption enhancement of semiconductor nanocrystals via Förster resonance energy transfer from cyanine J-aggregates. These J-aggregated dyes associate electrostatically with short quantum-dot (QD) ...

  6. Cryogenic spectroscopy of ultra-low density colloidal lead chalcogenide quantum dots on chip-scale optical cavities towards single quantum dot near-infrared cavity QED

    E-Print Network [OSTI]

    Ranojoy Bose; Jie Gao; James F. McMillan; Alex D. Williams; Chee Wei Wong

    2009-11-09T23:59:59.000Z

    We present evidence of cavity quantum electrodynamics from a sparse density of strongly quantum-confined Pb-chalcogenide nanocrystals (between 1 and 10) approaching single-dot levels on moderately high-Q mesoscopic silicon optical cavities. Operating at important near-infrared (1500-nm) wavelengths, large enhancements are observed from devices and strong modifications of the QD emission are achieved. Saturation spectroscopy of coupled QDs is observed at 77K, highlighting the modified nanocrystal dynamics for quantum information processing.

  7. Two photon luminescence from quantum dots using broad and narrowband ultrafast laser pulses

    E-Print Network [OSTI]

    Balasubramanian, Haribhaskar

    2008-10-10T23:59:59.000Z

    TWO PHOTON LUMINESCENCE FROM QUANTUM DOTS USING BROAD AND NARROWBAND ULTRAFAST LASER PULSES A Thesis by HARIBHASKAR BALASUBRAMANIAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment... of the requirements for the degree of MASTER OF SCIENCE December 2007 Major Subject: Biomedical Engineering TWO PHOTON LUMINESCENCE FROM QUANTUM DOTS USING BROAD AND NARROWBAND ULTRAFAST LASER PULSES A Thesis by HARIBHASKAR...

  8. Off-resonant coupling between a single quantum dot and a nanobeam photonic crystal cavity

    E-Print Network [OSTI]

    Armand Rundquist; Arka Majumdar; Jelena Vuckovic

    2011-10-05T23:59:59.000Z

    We demonstrate off-resonant coupling between a single quantum dot and a nanobeam photonic crystal cavity, under resonant excitation of the quantum dot or the cavity. These results are consistent with previous descriptions of off-resonant coupling as an incoherent phonon-mediated process. The extension of this phenomenon to a nanobeam photonic crystal cavity presents interesting possibilities for coherent control of this interaction by tailoring the phonon density of states.

  9. Ultrafast photon-photon interaction in a strongly coupled quantum dot-cavity system

    E-Print Network [OSTI]

    Dirk Englund; Arka Majumdar; Michal Bajcsy; Andrei Faraon; Pierre Petroff; Jelena vuckovic

    2011-07-14T23:59:59.000Z

    We study dynamics of the interaction between two weak light beams mediated by a strongly coupled quantum dot-photonic crystal cavity system. First, we perform all optical switching of a weak continuous-wave signal with a pulsed control beam, and then perform switching between two pulsed beams (40ps pulses) at the single photon level. Our results show that the quantum dot-nanocavity system creates strong, controllable interactions at the single photon level.

  10. Control of excitation transfer in coupled quantum dots by a nonresonant laser pulse

    E-Print Network [OSTI]

    P. A. Golovinski; V. A. Astapenko; A. V. Yakovets

    2014-08-06T23:59:59.000Z

    We study theoretically fast transfer of excitons between pairs of coupled quantum dots driven by the optical Stark effect that is produced by a short nonresonant laser pulse. The Schr\\"odinger equation, in which the relative position of energy levels of quantum dot subsystems is time-dependent, is solved numerically. Computer simulation shows a way to achieve efficient excitation transfer by the action of a picosecond laser pulse with a rectangular envelope function.

  11. SUNY/Buffalo Developing High-Efficiency Colloidal Quantum Dot Phosphors

    Broader source: Energy.gov [DOE]

    The State University of New York at Buffalo is working to reduce the cost and increase the performance of LEDs for general illumination by developing high-efficiency colloidal quantum dot phosphors to replace conventional phosphors (i.e., those placed directly on the chip). Colloidal quantum dot phosphors are nanocrystal emitters and contain no rare-earth elements. What's more, it's possible to tune the emission wavelength merely by changing their size.

  12. Electronic waiting-time distribution of a quantum-dot spin valve

    E-Print Network [OSTI]

    Björn Sothmann

    2014-10-27T23:59:59.000Z

    We discuss the electronic waiting-time distribution of a quantum-dot spin valve, i.e. a single-level quantum dot coupled to two ferromagnetic electrodes with magnetizations that can point in arbitrary directions. We demonstrate that the rich transport physics of this setup such as dynamical channel blockade and spin precession in an interaction-driven exchange field shows up in the waiting-time distribution and analyze the conditions necessary to observe the various effects.

  13. The effect of Coulomb interactions on thermoelectric properties of quantum dots

    SciTech Connect (OSTI)

    Zimbovskaya, Natalya A. [Department of Physics and Electronics, University of Puerto Rico-Humacao, CUH Station, Humacao, Puerto Rico 00791, USA and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Ruco 00931 (United States)] [Department of Physics and Electronics, University of Puerto Rico-Humacao, CUH Station, Humacao, Puerto Rico 00791, USA and Institute for Functional Nanomaterials, University of Puerto Rico, San Juan, Puerto Ruco 00931 (United States)

    2014-03-14T23:59:59.000Z

    Thermoelectric effects in a quantum dot coupled to the source and drain charge reservoirs are explored using a nonequilibrium Green's functions formalism beyond the Hartree-Fock approximation. Thermal transport is analyzed within a linear response regime. A transition from Coulomb blockade regime to Kondo regime in thermoelectric transport through a single-level quantum dot is traced using unified approximations for the relevant Green's functions.

  14. (In,Mn)As quantum dots: Molecular-beam epitaxy and optical properties

    SciTech Connect (OSTI)

    Bouravleuv, A. D., E-mail: bour@mail.ioffe.ru; Nevedomskii, V. N. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Ubyivovk, E. V. [St. Petersburg State University (Russian Federation)] [St. Petersburg State University (Russian Federation); Sapega, V. F. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Khrebtov, A. I. [St. Petersburg Academic University, Nanotechnology Research and Education Centre (Russian Federation)] [St. Petersburg Academic University, Nanotechnology Research and Education Centre (Russian Federation); Samsonenko, Yu. B.; Cirlin, G. E.; Ustinov, V. M. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)] [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-08-15T23:59:59.000Z

    Self-assembled (In,Mn)As quantum dots are synthesized by molecular-beam epitaxy on GaAs (001) substrates. The experimental results obtained by transmission electron microscopy show that doping of the central part of the quantum dots with Mn does not bring about the formation of structural defects. The optical properties of the samples, including those in external magnetic fields, are studied.

  15. GaN/AlN Quantum Dots for Single Qubit Emitters M. Winkelnkemper

    E-Print Network [OSTI]

    Nabben, Reinhard

    GaN/AlN Quantum Dots for Single Qubit Emitters M. Winkelnkemper , R. Seguin, S. Rodt, A. Hoffmann-plane GaN/AlN quantum dots (QDs) with focus on their potential as sources of single polarized photons emission lines from single InGaN/GaN [4­11] and GaN/AlN QDs grown on the c-plane [12­16] and a-plane [17

  16. Effect of quantum dot position and background doping on the performance of quantum dot enhanced GaAs solar cells

    SciTech Connect (OSTI)

    Driscoll, Kristina, E-mail: kmdsps@rit.edu; Bennett, Mitchell F.; Polly, Stephen J.; Forbes, David V.; Hubbard, Seth M., E-mail: smhsps@rit.edu [NanoPower Research Laboratories, Rochester Institute of Technology, Rochester, New York (United States)

    2014-01-13T23:59:59.000Z

    The effect of the position of InAs quantum dots (QD) within the intrinsic region of pin-GaAs solar cells is reported. Simulations suggest placing the QDs in regions of reduced recombination enables a recovery of open-circuit voltage (V{sub OC}). Devices with the QDs placed in the center and near the doped regions of a pin-GaAs solar cell were experimentally investigated. While the V{sub OC} of the emitter-shifted device was degraded, the center and base-shifted devices exhibited V{sub OC} comparable to the baseline structure. This asymmetry is attributed to background doping which modifies the recombination profile and must be considered when optimizing QD placement.

  17. Strain-induced fundamental optical transition in (In,Ga)As/GaP quantum dots

    SciTech Connect (OSTI)

    Robert, C., E-mail: cedric.robert@insa-rennes.fr, E-mail: cedric.robert@tyndall.ie; Pedesseau, L.; Cornet, C.; Jancu, J.-M.; Even, J.; Durand, O. [Université Européenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes, 35708 Rennes (France)] [Université Européenne de Bretagne, INSA Rennes, France and CNRS, UMR 6082 Foton, 20 Avenue des Buttes de Coësmes, 35708 Rennes (France); Nestoklon, M. O. [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation)] [Ioffe Physico-Technical Institute, Russian Academy of Sciences, 194021 St. Petersburg (Russian Federation); Pereira da Silva, K. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain) [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Departamento de Física, Universidade Federal do Ceará, P.O. Box 6030, Fortaleza–CE, 60455-970 (Brazil); Alonso, M. I. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain)] [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); Goñi, A. R. [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain) [ICMAB-CSIC, Campus UAB, 08193 Bellaterra (Spain); ICREA, Passeig Lluís Companys 23, 08010 Barcelona (Spain); Turban, P. [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France)] [Equipe de Physique des Surfaces et Interfaces, Institut de Physique de Rennes UMR UR1-CNRS 6251, Université de Rennes 1, F-35042 Rennes Cedex (France)

    2014-01-06T23:59:59.000Z

    The nature of the ground optical transition in an (In,Ga)As/GaP quantum dot is thoroughly investigated through a million atoms supercell tight-binding simulation. Precise quantum dot morphology is deduced from previously reported scanning-tunneling-microscopy images. The strain field is calculated with the valence force field method and has a strong influence on the confinement potentials, principally, for the conduction band states. Indeed, the wavefunction of the ground electron state is spatially confined in the GaP matrix, close to the dot apex, in a large tensile strain region, having mainly Xz character. Photoluminescence experiments under hydrostatic pressure strongly support the theoretical conclusions.

  18. A finite element analysis of a silicon based double quantum dot structure

    E-Print Network [OSTI]

    S. Rahman; J. Gorman; C. H. W. Barnes; D. A. Williams; H. P. Langtangen

    2006-04-06T23:59:59.000Z

    We present the results of a finite-element solution of the Laplace equation for the silicon-based trench-isolated double quantum-dot and the capacitively-coupled single-electron transistor device architecture. This system is a candidate for charge and spin-based quantum computation in the solid state, as demonstrated by recent coherent-charge oscillation experiments. Our key findings demonstrate control of the electric potential and electric field in the vicinity of the double quantum-dot by the electric potential applied to the in-plane gates. This constitutes a useful theoretical analysis of the silicon-based architecture for quantum information processing applications.

  19. Ultrafast dynamics of strongly coupled quantum dot-nanocavity systems

    E-Print Network [OSTI]

    Kai Müller; Kevin A. Fischer; Armand Rundquist; Constantin Dory; Konstantinos G. Lagoudakis; Tomas Sarmiento; Victoria Borish; Yousif A. Kelaita; Jelena Vu?kovi?

    2015-03-18T23:59:59.000Z

    We investigate the influence of exciton-phonon coupling on the dynamics of a strongly coupled quantum dot-photonic crystal cavity system and explore the effects of this interaction on different schemes for non-classical light generation. By performing time-resolved measurements, we map out the detuning-dependent polariton lifetime and extract the spectrum of the polariton-to-phonon coupling. Photon-blockade experiments are presented for different pulse-length and detuning conditions that are in very good agreement with quantum-optical simulations; we demonstrate that achieving high-fidelity photon blockade requires an intricate understanding of this parameter space. Furthermore, we show that detuned photon blockade, which is more efficient than resonant photon blockade, is also more dramatically affected by phonons. Finally, we achieve coherent control of the polariton states of a strongly coupled system and demonstrate that their efficient coupling to phonons can be exploited for novel concepts in high-fidelity single photon generation.

  20. Single-electron quantum dot in Si/SiGe with integrated charge sensing C. B. Simmons,a

    E-Print Network [OSTI]

    Coppersmith, Susan N.

    Single-electron quantum dot in Si/SiGe with integrated charge sensing C. B. Simmons,a Madhu that are important for quantum information processing. Si/SiGe is of interest for semiconductor spin qubits and measurement of a top-gated quantum dot occupied by a single electron in a Si/SiGe heterostructure. Transport

  1. Quasiresonant excitation of InP/InGaP quantum dots using second harmonic generated in a photonic crystal cavity

    E-Print Network [OSTI]

    Vuckovic, Jelena

    Quasiresonant excitation of InP/InGaP quantum dots using second harmonic generated in a photonic://apl.aip.org/about/rights_and_permissions #12;Quasiresonant excitation of InP/InGaP quantum dots using second harmonic generated in a photonic signal to noise quasiresonant excitation of InP/InGaP quantum dots. The excitation is provided via second

  2. Optical Properties of Wurtzite GaN and ZnO Quantum Dots Vladimir A. Fonoberov and Alexander A. Balandin

    E-Print Network [OSTI]

    Fonoberov, Vladimir

    Optical Properties of Wurtzite GaN and ZnO Quantum Dots Vladimir A. Fonoberov and Alexander A-Riverside, Riverside, California 92521, U.S.A. ABSTRACT We have investigated exciton states in wurtzite GaN/AlN and ZnO quantum dots. A strong piezoelectric field in GaN/AlN quantum dots is found to tilt conduction and valence

  3. Tunnel-injection GaN quantum dot ultraviolet light-emitting diodes

    SciTech Connect (OSTI)

    Verma, Jai; Kandaswamy, Prem Kumar; Protasenko, Vladimir; Verma, Amit; Grace Xing, Huili; Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)] [Department of Electrical Engineering, University of Notre Dame, Indiana 46556 (United States)

    2013-01-28T23:59:59.000Z

    We demonstrate a GaN quantum dot ultraviolet light-emitting diode that uses tunnel injection of carriers through AlN barriers into the active region. The quantum dot heterostructure is grown by molecular beam epitaxy on AlN templates. The large lattice mismatch between GaN and AlN favors the formation of GaN quantum dots in the Stranski-Krastanov growth mode. Carrier injection by tunneling can mitigate losses incurred in hot-carrier injection in light emitting heterostructures. To achieve tunnel injection, relatively low composition AlGaN is used for n- and p-type layers to simultaneously take advantage of effective band alignment and efficient doping. The small height of the quantum dots results in short-wavelength emission and are simultaneously an effective tool to fight the reduction of oscillator strength from quantum-confined Stark effect due to polarization fields. The strong quantum confinement results in room-temperature electroluminescence peaks at 261 and 340 nm, well above the 365 nm bandgap of bulk GaN. The demonstration opens the doorway to exploit many varied features of quantum dot physics to realize high-efficiency short-wavelength light sources.

  4. Electrically driven single photon emission from a CdSe/ZnSSe single quantum dot at 200?K

    SciTech Connect (OSTI)

    Quitsch, Wolf; Kümmell, Tilmar; Bacher, Gerd [Werkstoffe der Elektrotechnik and CENIDE, Universität Duisburg-Essen, Bismarckstraße 81, 47057 Duisburg (Germany); Gust, Arne; Kruse, Carsten; Hommel, Detlef [Institut für Festkörperphysik, Universität Bremen, Otto-Hahn-Allee 1, 28334 Bremen (Germany)

    2014-09-01T23:59:59.000Z

    High temperature operation of an electrically driven single photon emitter based on a single epitaxial quantum dot is reported. CdSe/ZnSSe/MgS quantum dots are embedded into a p-i-n diode architecture providing almost background free excitonic and biexcitonic electroluminescence from individual quantum dots through apertures in the top contacts. Clear antibunching with g{sup 2}(??=?0)?=?0.28?±?0.20 can be tracked up to T?=?200?K, representing the highest temperature for electrically triggered single photon emission from a single quantum dot device.

  5. Evaluating charge noise acting on semiconductor quantum dots in the circuit quantum electrodynamics architecture

    SciTech Connect (OSTI)

    Basset, J.; Stockklauser, A.; Jarausch, D.-D.; Frey, T.; Reichl, C.; Wegscheider, W.; Wallraff, A.; Ensslin, K.; Ihn, T. [Solid State Physics Laboratory, ETH Zurich, CH-8093 Zurich (Switzerland)

    2014-08-11T23:59:59.000Z

    We evaluate the charge noise acting on a GaAs/GaAlAs based semiconductor double quantum dot dipole-coupled to the voltage oscillations of a superconducting transmission line resonator. The in-phase (I) and the quadrature (Q) components of the microwave tone transmitted through the resonator are sensitive to charging events in the surrounding environment of the double dot with an optimum sensitivity of 8.5×10{sup ?5}?e/?(Hz). A low frequency 1/f type noise spectrum combined with a white noise level of 6.6×10{sup ?6} e{sup 2}/Hz above 1?Hz is extracted, consistent with previous results obtained with quantum point contact charge detectors on similar heterostructures. The slope of the 1/f noise allows to extract a lower bound for the double-dot charge qubit dephasing rate which we compare to the one extracted from a Jaynes-Cummings Hamiltonian approach. The two rates are found to be similar emphasizing that charge noise is the main source of dephasing in our system.

  6. Efficient Infrared-Emitting PbS Quantum Dots Grown on DNA and

    E-Print Network [OSTI]

    , the DNA-grown PbS nanocrystals exhibit a quantum-efficien- cy half-life of one week. We fabricate thin

  7. Sub-microsecond correlations in photoluminescence from InAs quantum dots

    E-Print Network [OSTI]

    Charles Santori; David Fattal; Jelena Vuckovic; Glenn S. Solomon; Edo Waks; Yoshihisa Yamamoto

    2003-08-16T23:59:59.000Z

    Photon correlation measurements reveal memory effects in the optical emission of single InAs quantum dots with timescales from 10 to 800 ns. With above-band optical excitation, a long-timescale negative correlation (antibunching) is observed, while with quasi-resonant excitation, a positive correlation (blinking) is observed. A simple model based on long-lived charged states is presented that approximately explains the observed behavior, providing insight into the excitation process. Such memory effects can limit the internal efficiency of light emitters based on single quantum dots, and could also be problematic for proposed quantum-computation schemes.

  8. Fast Electrical Control of a Quantum Dot Strongly Coupled to a Nano-resonator

    E-Print Network [OSTI]

    Andrei Faraon; Arka Majumdar; Hyochul Kim; Pierre Petroff; Jelena Vuckovic

    2009-06-03T23:59:59.000Z

    The resonance frequency of an InAs quantum dot strongly coupled to a GaAs photonic crystal cavity was electrically controlled via quantum confined Stark effect. Stark shifts up to 0.3meV were achieved using a lateral Schottky electrode that created a local depletion region at the location of the quantum dot. We report switching of a probe laser coherently coupled to the cavity up to speeds as high as 150MHz, limited by the RC constant of the transmission line. The coupling rate and the magnitude of the Stark shift with electric field were investigated while coherently probing the system.

  9. Nuclear Spin Dynamics in Double Quantum Dots: Multi-Stability, Dynamical Polarization, Criticality and Entanglement

    E-Print Network [OSTI]

    Martin J. A. Schuetz; Eric M. Kessler; Lieven M. K. Vandersypen; J. Ignacio Cirac; Geza Giedke

    2014-05-30T23:59:59.000Z

    We theoretically study the nuclear spin dynamics driven by electron transport and hyperfine interaction in an electrically-defined double quantum dot (DQD) in the Pauli-blockade regime. We derive a master-equation-based framework and show that the coupled electron-nuclear system displays an instability towards the buildup of large nuclear spin polarization gradients in the two quantum dots. In the presence of such inhomogeneous magnetic fields, a quantum interference effect in the collective hyperfine coupling results in sizable nuclear spin entanglement between the two quantum dots in the steady state of the evolution. We investigate this effect using analytical and numerical techniques, and demonstrate its robustness under various types of imperfections.

  10. Inhibition of plasmonically enhanced interdot energy transfer in quantum dot solids via photo-oxidation

    SciTech Connect (OSTI)

    Sadeghi, S. M. [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Nejat, A.; West, R. G. [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States)

    2012-11-15T23:59:59.000Z

    We studied the impact of photophysical and photochemical processes on the interdot Forster energy transfer in monodisperse CdSe/ZnS quantum dot solids. For this, we investigated emission spectra of CdSe/ZnS quantum dot solids in the vicinity of gold metallic nanoparticles coated with chromium oxide. The metallic nanoparticles were used to enhance the rate of the energy transfer between the quantum dots, while the chromium oxide coating led to significant increase of their photo-oxidation rates. Our results showed that irradiation of such solids with a laser beam can lead to unique spectral changes, including narrowing and blue shift. We investigate these effects in terms of inhibition of the plasmonically enhanced interdot energy transfer between quantum dots via the chromium-oxide accelerated photo-oxidation process. We demonstrate this considering energy-dependent rate of the interdot energy transfer process, plasmonic effects, and the way photo-oxidation enhances non-radiative decay rates of quantum dots with different sizes.

  11. Investigations of segregation phenomena in highly strained Mn-doped Ge wetting layers and Ge quantum dots embedded in silicon

    SciTech Connect (OSTI)

    Prestat, E., E-mail: eric.prestat@gmail.com; Porret, C.; Favre-Nicolin, V.; Tainoff, D.; Boukhari, M.; Bayle-Guillemaud, P.; Jamet, M.; Barski, A., E-mail: andre.barski@cea.com [INAC, SP2M, CEA and Université Joseph Fourier, 17 rue des Martyrs, 38054 Grenoble (France)

    2014-03-10T23:59:59.000Z

    In this Letter, we investigate manganese diffusion and the formation of Mn precipitates in highly strained, few monolayer thick, Mn-doped Ge wetting layers and nanometric size Ge quantum dot heterostructures embedded in silicon. We show that in this Ge(Mn)/Si system manganese always precipitates and that the size and the position of Mn clusters (precipitates) depend on the growth temperature. At high growth temperature, manganese strongly diffuses from germanium to silicon, whereas decreasing the growth temperature reduces the manganese diffusion. In the germanium quantum dots layers, Mn precipitates are detected, not only in partially relaxed quantum dots but also in fully strained germanium wetting layers between the dots.

  12. Impact of heavy hole-light hole coupling on optical selection rules in GaAs quantum dots

    SciTech Connect (OSTI)

    Belhadj, T.; Amand, T.; Kunz, S.; Marie, X.; Urbaszek, B. [INSA-CNRS-UPS, LPCNO, Universite de Toulouse, 135 Av. Rangueil, 31077 Toulouse (France); Kunold, A. [INSA-CNRS-UPS, LPCNO, Universite de Toulouse, 135 Av. Rangueil, 31077 Toulouse (France); Departamento de Ciencias Basicas, UAM-A, Col. Reynosa Tamaulipas, 02200 Mexico D.F. (Mexico); Simon, C.-M. [INSA-CNRS-UPS, LPCNO, Universite de Toulouse, 135 Av. Rangueil, 31077 Toulouse (France); CNRS-UPS, LCAR, IRSAMC, Universite de Toulouse, 31062 Toulouse (France); Kuroda, T.; Abbarchi, M.; Mano, T.; Sakoda, K. [National Institute for Material Science, Namiki 1-1, Tsukuba 305-0044 (Japan)

    2010-08-02T23:59:59.000Z

    We report strong heavy hole-light hole mixing in GaAs quantum dots grown by droplet epitaxy. Using the neutral and charged exciton emission as a monitor we observe the direct consequence of quantum dot symmetry reduction in this strain free system. By fitting the polar diagram of the emission with simple analytical expressions obtained from k{center_dot}p theory we are able to extract the mixing that arises from the heavy-light hole coupling due to the geometrical asymmetry of the quantum dot.

  13. Single hole quantum dot transistors in silicon Effendi Leobandung, Lingjie Guo, and Stephen Y. Choua)

    E-Print Network [OSTI]

    of the gate voltage have been observed at temperatures over 81 K and drain biases over 66 mV. The oscillations to the drain. As the gate voltage was scanned, the drain current i.e., the hole current oscil- lated Fig. 3-dot transistors were fabricated in silicon-on-insulator. Strong oscillations in the drain current as a function

  14. Using quantum dots to tag subsurface damage in lapped and polished glass samples

    SciTech Connect (OSTI)

    Williams, Wesley B.; Mullany, Brigid A.; Parker, Wesley C.; Moyer, Patrick J.; Randles, Mark H.

    2009-09-20T23:59:59.000Z

    Grinding, lapping, and polishing are finishing processes used to achieve critical surface parameters in a variety of precision optical and electronic components. As these processes remove material from the surface through mechanical and chemical interactions, they may induce a damaged layer of cracks, voids, and stressed material below the surface. This subsurface damage (SSD) can degrade the performance of a final product by creating optical aberrations due to diffraction, premature failure in oscillating components, and a reduction in the laser induced damage threshold of high energy optics. As these defects lie beneath the surface, they are difficult to detect, and while many methods are available to detect SSD, they can have notable limitations regarding sample size and type, preparation time, or can be destructive in nature. The authors tested a nondestructive method for assessing SSD that consisted of tagging the abrasive slurries used in lapping and polishing with quantum dots (nano-sized fluorescent particles). Subsequent detection of fluorescence on the processed surface is hypothesized to indicate SSD. Quantum dots that were introduced to glass surfaces during the lapping process were retained through subsequent polishing and cleaning processes. The quantum dots were successfully imaged by both wide field and confocal fluorescence microscopy techniques. The detected fluorescence highlighted features that were not observable with optical or interferometric microscopy. Atomic force microscopy and additional confocal microscope analysis indicate that the dots are firmly embedded in the surface but do not appear to travel deep into fractures beneath the surface. Etching of the samples exhibiting fluorescence confirmed that SSD existed. SSD-free samples exposed to quantum dots did not retain the dots in their surfaces, even when polished in the presence of quantum dots.

  15. Absorption spectra of CdSe-ZnS core-shell quantum dots at high photon energies : experiment and modeling

    E-Print Network [OSTI]

    Ghosh, Sandip

    Absorption spectra of CdSe-ZnS core-shell quantum dots at high photon energies : experiment spectra of CdSe-ZnS core-shell quantum dot (QD) ensembles, with average core diameters ranging from 2.6 nm. In agreement with previous reports, the absorption coefficient at energies 1 eV above the effective bandgap

  16. Excitonic properties of strained wurtzite and zinc-blende GaNAlxGa1xN quantum dots

    E-Print Network [OSTI]

    Fonoberov, Vladimir

    Excitonic properties of strained wurtzite and zinc-blende GaNÕAlxGa1ÀxN quantum dots Vladimir A 2003 We investigate exciton states theoretically in strained GaN/AlN quantum dots with wurtzite WZ of GaN QDs.1­8 Molecu- lar beam epitaxial growth in the Stranski­Krastanov mode of wurtzite WZ Ga

  17. Optical properties of wurtzite and zinc-blende GaNAlN quantum dots Vladimir A. Fonoberova)

    E-Print Network [OSTI]

    Fonoberov, Vladimir

    Optical properties of wurtzite and zinc-blende GaNÕAlN quantum dots Vladimir A. Fonoberova; published 20 August 2004 We investigate theoretically and compare optical properties of wurtzite and zincN/AlN interface governs optical properties of wurtzite quantum dots while having a small effect on zinc

  18. Getting Informations of Wavefunctions in Quantum Dots from the Fano Effect Shingo KATSUMOTO, Hisashi AIKAWA, Kensuke KOBAYASHI and Yasuhiro IYE

    E-Print Network [OSTI]

    Iye, Yasuhiro

    by around Coulomb (resonant) peaks obeying the Breit-Wigner law. On the other hand, there appeared-phase Coulomb peaks" in quantum dots. KEYWORDS: quantum dot, Fano effect, phase shift, AB effect 1. Introduction of the phase shift just at the Coulomb peaks. This was soon turned out to be a kind of artifact due to the two

  19. Microsphere Light-Scattering Layer Assembled by ZnO Nanosheets for the Construction of High Efficiency (>5%) Quantum Dots

    E-Print Network [OSTI]

    Cao, Guozhong

    performance solar cells for sustainable energy sources to replace fossil fuels has become an urgent subject for CdS/CdSe quantum dot cosensitized solar cells (QDSCs) with a power conversion efficiency (PCE Efficiency (>5%) Quantum Dots Sensitized Solar Cells Jianjun Tian,*, Lili Lv, Xuyang Wang, Chengbin Fei

  20. Showcasing the research of quantum dot sensitized solar cells from Prof. J.J.Tian's and Prof. G.Z.Cao's lab,

    E-Print Network [OSTI]

    Cao, Guozhong

    . Introduction Quantum dot sensitized solar cells (QDSCs) can be regarded as a derivative of dye-sensitized solarShowcasing the research of quantum dot sensitized solar cells from Prof. J.J.Tian's and Prof. G cells A hierarchical structure of ZnO/TiO2 nanocable photoanode for quantum dot sensitized solar cells

  1. Large internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko, Gerald Hnig, Christian Kindel, Sven Rodt, Andr Strittmatter et al.

    E-Print Network [OSTI]

    Nabben, Reinhard

    Large internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko, Gerald Hönig, Christian transitions in wurtzite InGaN/GaN coupled quantum dot nanowire heterostructures with polarization internal dipole moment in InGaN/GaN quantum dots Irina A. Ostapenko,a Gerald Hönig, Christian Kindel, Sven

  2. Mn solid solutions in self-assembled Ge/Si (001) quantum dot heterostructures

    SciTech Connect (OSTI)

    Kassim, J.; Nolph, C.; Reinke, P.; Floro, J. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Jamet, M. [Institut Nanosciences et Cryogenie/SP2M, CEA-UJF, F-38054 Grenoble (France)

    2012-12-10T23:59:59.000Z

    Heteroepitaxial Ge{sub 0.98}Mn{sub 0.02} quantum dots (QDs) on Si (001) were grown by molecular beam epitaxy. The standard Ge wetting layer-hut-dome-superdome sequence was observed, with no indicators of second phase formation in the surface morphology. We show that Mn forms a dilute solid solution in the Ge quantum dot layer, and a significant fraction of the Mn partitions into a sparse array of buried, Mn-enriched silicide precipitates directly underneath a fraction of the Ge superdomes. The magnetic response from the ultra-thin film indicates the absence of robust room temperature ferromagnetism, perhaps due to anomalous intermixing of Si into the Ge quantum dots.

  3. Design of quantum dot lattices in amorphous matrices by ion beam irradiation

    SciTech Connect (OSTI)

    Buljan, M.; Bogdanovic-Radovic, I.; Karlusic, M.; Desnica, U. V.; Radic, N.; Jaksic, M.; Salamon, K.; Drazic, G.; Bernstorff, S.; Holy, V. [Rudjer Boskovic Institute, Bijenicka cesta 54, HR-10000 Zagreb (Croatia); Institute of Physics, Bijenicka cesta 46, HR-10000 Zagreb (Croatia); Jozef Stefan Institute, Jamova 39, SLO-1000 Ljubljana (Slovenia); Sincrotrone Trieste, I-34149 Basovizza (Italy); Charles University in Prague, CZ-12116 Prague (Czech Republic)

    2011-10-15T23:59:59.000Z

    We report on the highly controllable self-assembly of semiconductor quantum dots and metallic nanoparticles in a solid amorphous matrix, induced by ion beam irradiation of an amorphous multilayer. We demonstrate experimentally and theoretically a possibility to tune the basic structural properties of the quantum dots in a wide range. Furthermore, the sizes, distances, and arrangement type of the quantum dots follow simple equations dependent on the irradiation and the multilayer properties. We present a Monte Carlo model for the simulation and prediction of the structural properties of the materials formed by this method. The presented results enable engineering and simple production of functional materials or simple devices interesting for applications in nanotechnology.

  4. Photoinduced band filling in strongly confined colloidal PbS quantum dots

    SciTech Connect (OSTI)

    Ullrich, B., E-mail: bruno@fis.unam.mx [Instituto de Ciencias Físicas, Universidad Nacional Autónoma de México, Cuernavaca, Morelos 62210 (Mexico); Ullrich Photonics LLC, Wayne, Ohio 43466 (United States); Xi, H. [Department of Physics and Astronomy, Bowling Green State University, Bowling Green, Ohio 43403-0209 (United States); Wang, J. S. [Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright Patterson AFB, Ohio 45433-7707 (United States)

    2014-06-21T23:59:59.000Z

    Increase in continuous wave laser excitation (6?W/cm{sup 2} to 120?W/cm{sup 2}) of colloidal PbS quantum dots in the strongly quantized regime (diameters 2.0?nm and 4.7?nm) deposited on semi-insulating GaAs and glass causes a clear blue shift (0.019?eV and 0.080?eV) of the emission spectra. Proof of the applicability of a dynamic three-dimensional band filling model is the significance of the presented results and demonstrates the effective electronic coupling in quantum dot arrays similar to superlattices. The work also reveals the influence of quantum dot sizes on photo-doping effects.

  5. Decoherence and Quantum Interference assisted electron trapping in a quantum dot

    E-Print Network [OSTI]

    Ahmed El Halawany; Michael N. Leuenberger

    2013-08-08T23:59:59.000Z

    We present a theoretical model for the dynamics of an electron that gets trapped by means of decoherence and quantum interference in the central quantum dot (QD) of a semiconductor nanoring (NR) made of five QDs, between 100 K and 300 K. The electron's dynamics is described by a master equation with a Hamiltonian based on the tight-binding model, taking into account electron-LO phonon interaction (ELOPI). Based on this configuration, the probability to trap an electron with no decoherence is almost 27%. In contrast, the probability to trap an electron with decoherence is 70% at 100 K, 63% at 200 K and 58% at 300 K. Our model provides a novel method of trapping an electron at room temperature.

  6. Investigation of steady-state and time-dependent luminescence properties of colloidal InGaP quantum dots

    E-Print Network [OSTI]

    Chatterjee, Subhasish; Menon, Vinod M

    2012-01-01T23:59:59.000Z

    Quantum dots play a promising role in the development of novel optical and biosensing devices. In this study, we investigated steady-state and time-dependent luminescence properties of InGaP/ZnS core/shell colloidal quantum dots in a solution phase at room temperature. The steady state experiments exhibited an emission maximum at 650 nm with full width at half maximum of ~ 85 nm, and strong first-excitonic absorption peak at 600 nm. The time-resolved luminescence measurements depicted a bi-exponential decay profile with lifetimes of {\\tau}1\\sim 47 ns and {\\tau} 2\\sim 142 ns at the emission maximum. Additionally, luminescence quenching and lifetime reduction due to resonance energy transfer between the quantum dot and an absorber are demonstrated. Our results support the plausibility of using these InGaP quantum dots as an effective alternative to highly toxic conventional Cd or Pb based colloidal quantum dots for biological applications.

  7. Gain and tuning characteristics of mid-infrared InSb quantum dot diode lasers

    SciTech Connect (OSTI)

    Lu, Q.; Zhuang, Q.; Hayton, J.; Yin, M.; Krier, A. [Physics Department, Lancaster University, Lancaster LA1 4YB (United Kingdom)

    2014-07-21T23:59:59.000Z

    There have been relatively few reports of lasing from InSb quantum dots (QDs). In this work, type II InSb/InAs QD laser diodes emitting in the mid-infrared at 3.1??m have been demonstrated and characterized. The gain was determined to be 2.9?cm{sup ?1} per QD layer, and the waveguide loss was ?15?cm{sup ?1} at 4?K. Spontaneous emission measurements below threshold revealed a blue shift of the peak wavelength with increasing current, indicating filling of ground state heavy hole levels in the QDs. The characteristic temperature, T{sub 0}?=?101?K below 50?K, but decreased to 48?K at higher temperatures. The emission wavelength of these lasers showed first a blue shift followed by a red shift with increasing temperature. A hybrid structure was used to fabricate the laser by combining a liquid phase epitaxy grown p-InAs{sub 0.61}Sb{sub 0.13}P{sub 0.26} lower cladding layer and an upper n{sup +} InAs plasmon cladding layer which resulted in a maximum operating temperature (T{sub max}) of 120?K in pulsed mode, which is the highest reported to date.

  8. Energy levels of double triangular graphene quantum dots

    SciTech Connect (OSTI)

    Liang, F. X.; Jiang, Z. T., E-mail: ztjiang616@hotmail.com; Zhang, H. Y.; Li, S. [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); Lv, Z. T. [School of Physics, Beijing Institute of Technology, Beijing 100081 (China); School of Physical Science and Information Engineering, Liaocheng University, Liaocheng 252059 (China)

    2014-09-28T23:59:59.000Z

    We investigate theoretically the energy levels of the coupled double triangular graphene quantum dots (GQDs) based on the tight-binding Hamiltonian model. The double GQDs including the ZZ-type, ZA-type, and AA-type GQDs with the two GQDs having the zigzag or armchair boundaries can be coupled together via different interdot connections, such as the direct coupling, the chains of benzene rings, and those of carbon atoms. It is shown that the energy spectrum of the coupled double GQDs is the amalgamation of those spectra of the corresponding two isolated GQDs with the modification triggered by the interdot connections. The interdot connection is inclined to lift up the degeneracies of the energy levels in different degree, and as the connection changes from the direct coupling to the long chains, the removal of energy degeneracies is suppressed in ZZ-type and AA-type double GQDs, which indicates that the two coupled GQDs are inclined to become decoupled. Then we consider the influences on the spectra of the coupled double GQDs induced by the electric fields applied on the GQDs or the connection, which manifests as the global spectrum redistribution or the local energy level shift. Finally, we study the symmetrical and asymmetrical energy spectra of the double GQDs caused by the substrates supporting the two GQDs, clearly demonstrating how the substrates affect the double GQDs' spectrum. This research elucidates the energy spectra of the coupled double GQDs, as well as the mechanics of manipulating them by the electric field and the substrates, which would be a significant reference for designing GQD-based devices.

  9. Growth and optical characterization of multilayers of InGaN quantum dots

    E-Print Network [OSTI]

    Zhu, Tontong; El-Ella, Haitham; Reid, Benjamin; Holmes, Mark; Taylor, Robert; Kappers, Menno; Oliver, Rachel

    2012-01-01T23:59:59.000Z

    carried out using a two photon excitation technique employing a picosecond mode-locked Ti-sapphire laser emitting at 790 nm. Samples were mounted in a cold -finger cryostat that could be cooled down to 4.2 K and the laser was focused through a microscope... GaN quantum dots Article Type: Research Paper Section/Category: General subjects Keywords: B2. InGaN quantum dots; A1. Photoluminescence; B1. Nitrides; A3. Metal-organic vapour phase epitaxy Corresponding Author: Dr Tongtong Zhu, Ph...

  10. An Efficient Source of Single Photons: A Single Quantum Dot in a Micropost Microcavity

    E-Print Network [OSTI]

    Matthew Pelton; Charles Santori; Jelena Vuckovic; Bingyang Zhang; Glenn S. Solomon; Jocelyn Plant; Yoshihisa Yamamoto

    2002-08-08T23:59:59.000Z

    We have demonstrated efficient production of triggered single photons by coupling a single semiconductor quantum dot to a three-dimensionally confined optical mode in a micropost microcavity. The efficiency of emitting single photons into a single-mode travelling wave is approximately 38%, which is nearly two orders of magnitude higher than for a quantum dot in bulk semiconductor material. At the same time, the probability of having more than one photon in a given pulse is reduced by a factor of seven as compared to light with Poissonian photon statistics.

  11. Temperature dependency of the emission properties from positioned In(Ga)As/GaAs quantum dots

    SciTech Connect (OSTI)

    Braun, T.; Schneider, C.; Maier, S.; Forchel, A.; Höfling, S.; Kamp, M. [Technische Physik, Physikalisches Institut and Wilhelm Conrad Röntgen-Research Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074, Würzburg (Germany); Igusa, R.; Iwamoto, S.; Arakawa, Y. [University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505 (Japan)

    2014-09-15T23:59:59.000Z

    In this letter we study the influence of temperature and excitation power on the emission linewidth from site-controlled InGaAs/GaAs quantum dots grown on nanoholes defined by electron beam lithography and wet chemical etching. We identify thermal electron activation as well as direct exciton loss as the dominant intensity quenching channels. Additionally, we carefully analyze the effects of optical and acoustic phonons as well as close-by defects on the emission linewidth by means of temperature and power dependent micro-photoluminescence on single quantum dots with large pitches.

  12. Green's functions technique for calculating the emission spectrum in a quantum dot-cavity system

    E-Print Network [OSTI]

    Edgar A. Gomez; J. D. Hernandez-Rivero; Herbert Vinck-Posada

    2015-02-01T23:59:59.000Z

    We introduce the Green's functions technique as an alternative theory to the quantum regression theorem formalism for calculating the two-time correlation functions in open quantum systems. In particular, we investigate the potential of this theoretical approach by its application to compute the emission spectrum of a dissipative system composed by a single quantum dot inside of a semiconductor cavity. We also describe a simple algorithm based on the Green's functions technique for calculating the emission spectrum of the quantum dot as well as of the cavity which can easily be implemented in any numerical linear algebra package. We find that the Green's functions technique demonstrates a better accuracy and efficiency in the calculation of the emission spectrum and it allows to overcome the inherent theoretical difficulties associated to the direct application of the quantum regression theorem approach.

  13. Graphene quantum dots for valley-based quantum computing: A feasibility study

    E-Print Network [OSTI]

    G. Y. Wu; N. -Y. Lue; L. Chang

    2011-04-21T23:59:59.000Z

    At the center of quantum computing1 realization is the physical implementation of qubits - two-state quantum information units. The rise of graphene2 has opened a new door to the implementation. Because graphene electrons simulate two-dimensional relativistic particles with two degenerate and independent energy valleys,3 a novel degree of freedom (d.o.f.), namely, the valley state of an electron, emerges as a new information carrier.4 Here, we expand the Loss-DiVincenzo quantum dot (QD) approach in electron spin qubits,5,6 and investigate the feasibility of double QD (DQD) structures in gapful graphene as "valley qubits", with the logic 0 / 1 states represented by the "valley" singlet / triplet pair. This generalization is characterized by 1) valley relaxation time ~ O(ms), and 2) electric qubit manipulation on the time scale ~ ns, based on the 1st-order "relativistic effect" unique in graphene. A potential for valley-based quantum computing is present.

  14. Nanoscale optical positioning of single quantum dots for bright, pure, and on-demand single-photon emission

    E-Print Network [OSTI]

    Sapienza, Luca; Badolato, Antonio; Srinivasan, Kartik

    2015-01-01T23:59:59.000Z

    Self-assembled, epitaxially-grown InAs/GaAs quantum dots are promising semiconductor quantum emitters that can be integrated on a chip for a variety of photonic quantum information science applications. However, self-assembled growth results in an essentially random in-plane spatial distribution of quantum dots, presenting a challenge in creating devices that exploit the strong interaction of single quantum dots with highly confined optical modes. Here, we present a photoluminescence imaging approach for locating single quantum dots with respect to alignment features with an average (minimum) position uncertainty efficiency (48 % +/- 5 % into a 0.4 numerical aperture lens, close to the theoretically predicted value of 50 %), low multiphoton prob...

  15. High-brightness single photon source from a quantum dot in a directional-emission nanocavity

    E-Print Network [OSTI]

    Mitsuru Toishi; Dirk Englund; Andrei Faraon; Jelena Vuckovic

    2009-04-08T23:59:59.000Z

    We analyze a single photon source consisting of an InAs quantum dot coupled to a directional-emission photonic crystal (PC) cavity implemented in GaAs. On resonance, the dot's lifetime is reduced by more than 10 times, to 45ps. Compared to the standard three-hole defect cavity, the perturbed PC cavity design improves the collection efficiency into an objective lens (NA=0.75) by factor 6, and improves the coupling efficiency of the collected light into a single mode fiber by factor 1.9. The emission frequency is determined by the cavity mode, which is antibunched to g(2)=0.05. The cavity design also enables efficient coupling to a higher-order cavity mode for local optical excitation of cavity-coupled quantum dots.

  16. Engineering the quantum point contact response to single-electron charging in a few-electron quantum-dot circuit

    E-Print Network [OSTI]

    -electron quantum-dot circuit L.-X. Zhang and J. P. Leburtona) Beckman Institute for Advanced Science & Technology Project, Delft University of Technology, P.O. Box 5046, 2600 GA Delft, The Netherlands (Received 3 May =e2 /h (which is halfway between pinch off and the first con- ductance plateau G0=2e2 /h) gives

  17. Intermediate-band solar cells based on quantum dot supracrystals Q. Shao and A. A. Balandina

    E-Print Network [OSTI]

    parameter in the photovoltaic PV solar cell technology. It is defined as = FFVocJsc Pin , 1 where FFIntermediate-band solar cells based on quantum dot supracrystals Q. Shao and A. A. Balandina Nano to implement the intermediate-band solar cell with the efficiency exceeding the Shockley-Queisser limit

  18. A Surface Plasmon Enhanced Infrared Photodetector Based on InAs Quantum Dots

    E-Print Network [OSTI]

    Krishna, Sanjay

    A Surface Plasmon Enhanced Infrared Photodetector Based on InAs Quantum Dots Chun-Chieh Chang-QD photodetector can facilitate a strong plasmonic-QD interaction, leading to a 130% absolute enhancement of infrared photoresponse at the plasmonic resonance. Our study indicates two key mechanisms

  19. Distance-Engineered Plasmon-Enhanced Light Harvesting in CdSe Quantum Dots

    E-Print Network [OSTI]

    Distance-Engineered Plasmon-Enhanced Light Harvesting in CdSe Quantum Dots Shengye Jin,,§, Erica De) is essential for the development of efficient QD-based solar energy conversion systems. In this study, plasmon as a function of interparticle (QD to Ag NP) distance. Up to 24-fold plasmonic enhancement of fluorescence from

  20. Spin States in Graphene Quantum Dots J. Guttinger,* T. Frey, C. Stampfer,

    E-Print Network [OSTI]

    Ihn, Thomas

    is connected via tunneling constrictions to source (s) and drain (d) contacts. It is tunable by the back gate with a base tempera- ture of 90 mK. The source-drain conductance of the device measured over a large back gate) Quantum dot source-drain con- ductance for varying back gate voltage (Vb ¼ 100 V). (b) Coulomb diamond

  1. Fine Structure of Highly Charged Excitons in Semiconductor Quantum Dots B. Urbaszek,1

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    quantum dots (QDs) are artificial atoms whose properties can be individually measured in their solid, the degeneracy of the excitonic ground state is lifted by the electron-hole (EH) exchange interaction, resultingV, they can be much larger in semiconductor nanocrystals [3] or polymers [4]. In all these systems

  2. Targeting quantum dots to surface proteins in living cells with biotin ligase

    E-Print Network [OSTI]

    coli biotin ligase site-specifically biotinylates a lysine side chain within a 15-amino acid acceptor molecule Quantum dots (QDs) are semiconductor nanoparticles that greatly expand the possibilities target the functional groups of one protein amidst all of the other expressed proteins containing

  3. Theoretical performance of solar cell based on mini-bands quantum dots

    SciTech Connect (OSTI)

    Aly, Abou El-Maaty M., E-mail: drabouelmaaty@hotmail.com, E-mail: ashraf.nasr@gmail.com [Power Electronics and Energy Conversion Department, ERI, NRCB (Egypt); College of Computer, Qassim University, P.O.B. 6688, Buryadah 51453 (Saudi Arabia); Nasr, A., E-mail: drabouelmaaty@hotmail.com, E-mail: ashraf.nasr@gmail.com [Radiation Engineering Department, NCRRT, Atomic Energy Authority (Egypt); College of Computer, Qassim University, P.O.B. 6688, Buryadah 51453 (Saudi Arabia)

    2014-03-21T23:59:59.000Z

    The tremendous amount of research in solar energy is directed toward intermediate band solar cell for its advantages compared with the conventional solar cell. The latter has lower efficiency because the photons have lower energy than the bandgap energy and cannot excite mobile carriers from the valence band to the conduction band. On the other hand, if mini intermediate band is introduced between the valence and conduction bands, then the smaller energy photons can be used to promote charge carriers transfer to the conduction band and thereby the total current increases while maintaining a large open circuit voltage. In this article, the influence of the new band on the power conversion efficiency for structure of quantum dots intermediate band solar cell is theoretically investigated and studied. The time-independent Schrödinger equation is used to determine the optimum width and location of the intermediate band. Accordingly, achievement of a maximum efficiency by changing the width of quantum dots and barrier distances is studied. Theoretical determination of the power conversion efficiency under the two different ranges of QD width is presented. From the obtained results, the maximum power conversion efficiency is about 70.42%. It is carried out for simple cubic quantum dot crystal under fully concentrated light. It is strongly dependent on the width of quantum dots and barrier distances.

  4. Photovoltaic nanopillar radial junction diode architecture enhanced by integrating semiconductor quantum dot nanocrystals as light harvesters

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    Photovoltaic nanopillar radial junction diode architecture enhanced by integrating semiconductor hybridized, radial p-n junction based, nanopillar solar cells with photovoltaic performance enhanced. By furnishing Si based nanopillar photovoltaic diodes with CdSe quantum dots, we experimentally showed up

  5. Cu2ZnSnS4 nanocrystals and graphene quantum dots for photovoltaics Xukai Xinab

    E-Print Network [OSTI]

    Lin, Zhiqun

    Cu2ZnSnS4 nanocrystals and graphene quantum dots for photovoltaics Jun Wang,a Xukai Xinab advances in the synthesis and utilization of CZTS nanocrystals and colloidal GQDs for photovoltaics emerged to achieve low cost, high perfor- mance photovoltaics, including organic solar cells,2­6 dye

  6. Coupling an electron spin in a semiconductor quantum dot to an optical nano-cavity

    E-Print Network [OSTI]

    Arka Majumdar; Per Kaer; Michal Bajcsy; Erik D. Kim; Konstantinos G. Lagoudakis; Armand Rundquist; Jelena Vuckovic

    2013-04-07T23:59:59.000Z

    We propose a scheme to efficiently couple a single quantum dot electron spin to an optical nano-cavity, which enables us to simultaneously benefit from a cavity as an efficient photonic interface, as well as to perform high fidelity (nearly 100%) spin initialization and manipulation achievable in bulk semiconductors. Moreover, the presence of the cavity speeds up the spin initialization process beyond GHz.

  7. Influence of pair coherence on charge tunneling through a quantum dot connected to a superconducting lead

    E-Print Network [OSTI]

    Domanski, Tadeusz

    Influence of pair coherence on charge tunneling through a quantum dot connected the temperature below T* larger than Tc the single particle states become gradually depleted over a certain energy to a close neighborhood to the Mott insulating state, or because of competition with some other types

  8. Effect of the (OH) Surface Capping on ZnO Quantum Dots

    E-Print Network [OSTI]

    Nabben, Reinhard

    in air at different temperatures from 150­500 C for 30 min. In comparison, highly purified bulk Zn is related to oxygen deficiency [1]; the other is a much narrower ultraviolet (UV) emission band at around, compared with good quality ZnO single crystals or ZnO powders, the UV bandgap luminescence in quantum dots

  9. Enhanced quantum dot optical down-conversion using asymmetric 2D photonic crystals

    E-Print Network [OSTI]

    Cunningham, Brian

    -performance crosslinked colloidal quantum-dot light-emitting diodes," Nat. Photonics 3(6), 341­345 (2009). 10. D. Englund. Medvedev, M. Kazes, S. H. Kan, and U. Banin, "Efficient near-infrared polymer nanocrystal light- emitting diodes," Science 295(5559), 1506­1508 (2002). 8. V. Wood, M. J. Panzer, J. L. Chen, M. S. Bradley, J. E

  10. Electronic structure of wurtzite quantum dots with cylindrical symmetry L. C. Lew Yan Voona

    E-Print Network [OSTI]

    Melnik, Roderick

    Electronic structure of wurtzite quantum dots with cylindrical symmetry L. C. Lew Yan Voona July 2005 This paper presents a six-band k·p theory for wurtzite semiconductor nanostructures to the Rashba-Sheka-Pikus Hamiltonian for wurtzite semiconductors, without the need for the axial approximation

  11. Wave-Function Mapping of Graphene Quantum Dots with Soft Confinement D. Subramaniam,1

    E-Print Network [OSTI]

    Florian, Libisch

    Wave-Function Mapping of Graphene Quantum Dots with Soft Confinement D. Subramaniam,1 F. Libisch,2) Using low-temperature scanning tunneling spectroscopy, we map the local density of states of graphene the graphene K point, the electronic properties of the QDs are dominantly graphenelike. Indeed, we compare

  12. Whispering-Gallery Modes in Quantum Dot Embedded Microspheres for Sensing Applications

    E-Print Network [OSTI]

    Beier, Hope T.

    2011-02-22T23:59:59.000Z

    that shift position with variations in the local index of refraction sampled by the evanescent tail of the WGMs. To excite these WGMs, we embed quantum dots (QDs) in the periphery of polystyrene microspheres to serve as local light sources. By coupling...

  13. Role of Symmetry Breaking on the Optical Transitions in Lead-Salt Quantum Dots

    E-Print Network [OSTI]

    Van Stryland, Eric

    Role of Symmetry Breaking on the Optical Transitions in Lead-Salt Quantum Dots Gero Nootz to explain optical transitions in lead-salt QDs. Thus, while the band anisotropy of the bulk semiconductor functions. These studies clarify the controversy of the origin of spectral features in lead-salt QDs

  14. Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous

    E-Print Network [OSTI]

    Demir, Hilmi Volkan

    Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy NQD-LED design with both high luminous efficacy of optical radiation and CRI is presented to have luminous efficacy of optical ra- diation (LER), which is challenging using conventional phosphors

  15. Depleted-heterojunction colloidal quantum dot photovoltaics employing low-cost electrical contacts

    E-Print Network [OSTI]

    Department of Materials Science and Engineering, 184 College Street, Toronto, Ontario M5S 3E4, Canada 3 of depleted-heterojunction colloidal quantum dot solar cells, we describe herein a strategy that replaces. © 2010 American Institute of Physics. doi:10.1063/1.3463037 Solar energy harvesting requires

  16. Prospective Article Materials processing strategies for colloidal quantum dot solar cells

    E-Print Network [OSTI]

    energy sources, particularly with cheap and plentiful natural gas, solar photovoltaic systems must cost of the solar panels themselves. Third-generation photovoltaic systems, including organic, dye-sensitized, and colloidal quantum dot (CQD) solar cells, offer a path to low-weight, low-cost, and prospectively high

  17. PHYSICAL REVIEW B 85, 085117 (2012) Spin thermopower in interacting quantum dots

    E-Print Network [OSTI]

    Ramsak, Anton

    2012-01-01T23:59:59.000Z

    renormalization group method, we investigate the spin thermopower of a quantum dot in a magnetic field, the dependence of the spin-Seebeck coefficient on the temperature and the magnetic field is explained in terms applications, including power generation, refrigeration, and temperature measurement.1 Thermoelectric phenomena

  18. Study of the self-organization processes in lead sulfide quantum dots

    SciTech Connect (OSTI)

    Tarasov, S. A., E-mail: SATarasov@mail.ru; Aleksandrova, O. A.; Maksimov, A. I.; Maraeva, E. V.; Matyushkin, L. B.; Men’kovich, E. A.; Moshnikov, V. A. [St. Petersburg Electrotechnical University LETI (Russian Federation); Musikhin, S. F. [St. Petersburg State Polytechnic University (Russian Federation)

    2014-12-15T23:59:59.000Z

    A procedure is described for the synthesis of nanoparticles based on lead chalcogenides. The procedure combines the synthesis of colloidal quantum dots (QDs) in aqueous solutions with simultaneous organization of the QDs into ordered arrays. The processes of the self-organization of QDs are analyzed at the nano- and microscopic levels by the photoluminescence method, atomic-force microscopy, and optical microscopy.

  19. Fabrication and characterization of face-centered-cubic void dots photonic crystals in a solid polymer material

    SciTech Connect (OSTI)

    Zhou Guangyong; Ventura, Michael James; Vanner, Michael Ross; Gu Min [Centre for Micro-Photonics and CUDOS, Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, P.O. Box 218, Hawthorn, Victoria 3122 (Australia)

    2005-01-03T23:59:59.000Z

    Spherical void dots with a diameter of 1.2-1.8 {mu}m have been generated in a solid polymer material by use of the ultrafast laser driven micro-explosion method. Micron-sized structures with a face-centered cubic lattice stacked in the [100] and [111] directions have been fabricated. Confocal microscopic images show the high uniformity of the fabricated structures. Photonic stopgaps with a suppression rate of approximately 70% as well as the second-order stopgaps have been observed in both directions. It is shown that the dependence of the stopgaps on the illumination angle in the [100] direction is significantly different from that in the [111] direction.

  20. Preparation of Non-equilibrium Nuclear Spin States in Double Quantum Dots

    E-Print Network [OSTI]

    M. Gullans; J. J. Krich; J. M. Taylor; B. I. Halperin; M. D. Lukin

    2014-07-25T23:59:59.000Z

    We theoretically study the dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. In our prior work [Phys. Rev. Lett. 104, 226807 (2010)] we identified three regimes of long-term dynamics, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. In particular, when the dots are different sizes we found that the Overhauser field becomes larger in the smaller dot. Here we present a detailed theoretical analysis of these problems including a model of the polarization dynamics and the development of a new numerical method to efficiently simulate semiclassical central-spin problems. When nuclear spin noise is included, the results agree with our prior work indicating that large difference fields and dark states are stable configurations, while the elimination of the difference field is unstable; however, in the absence of noise we find all three steady states are achieved depending on parameters. These results are in good agreement with dynamic nuclear polarization experiments in double quantum dots.

  1. Controlling the nuclear polarization in quantum dots using optical pulses with a modest bandwidth

    E-Print Network [OSTI]

    S. G. Carter; Sophia E. Economou; A. Shabaev; A. S. Bracker

    2011-02-02T23:59:59.000Z

    We show that detuned optical pulse trains with a modest spectral width can polarize nuclear spins in InAs quantum dots. The pulse bandwidth is large enough to excite a coherent superposition of both electron spin eigenstates in these negatively charged dots but narrow enough to give partial spectral selectivity between the eigenstates. The coherent precession of electron spin states and periodic excitation focuses the nuclear spin distribution, producing a discrete set of precession modes. The spectral selectivity generates a net nuclear polarization, through a mechanism that relies on optical spin rotations rather than electron spin relaxation.

  2. Photo-induced conductance fluctuations in mesoscopic Ge/Si systems with quantum dots

    SciTech Connect (OSTI)

    Stepina, N. P.; Dvurechenskii, A. V.; Nikiforov, A. I. [Institute of Semiconductor Physics, 630090 Novosibirsk (Russian Federation); Moers, J.; Gruetzmacher, D. [Institute of Bio- and Nanosystems, Forschungszentrum Julich GmbH 52425 Julich (Germany)

    2014-08-20T23:59:59.000Z

    We study the evolution of electron transport in strongly localized mesoscopic system with quantum dots under small photon flux. Exploring devices with narrow transport channels lead to the observation of giant fluctuations of the photoconductance, which is attributed to the strong dependence of hopping current on the filling of dots by holes. In our experiments, single-photon mode operation is indicated by the linear dependence of the frequency of photo-induced fluctuations on the light intensity and the step-like response of conductance on the pulse excitation. The effect of the light wavelength, measurement temperature, size of the conductive channel on the device efficiency are considered.

  3. Full counting statistics as a probe of quantum coherence in a side-coupled double quantum dot system

    SciTech Connect (OSTI)

    Xue, Hai-Bin, E-mail: xuehaibin@tyut.edu.cn

    2013-12-15T23:59:59.000Z

    We study theoretically the full counting statistics of electron transport through side-coupled double quantum dot (QD) based on an efficient particle-number-resolved master equation. It is demonstrated that the high-order cumulants of transport current are more sensitive to the quantum coherence than the average current, which can be used to probe the quantum coherence of the considered double QD system. Especially, quantum coherence plays a crucial role in determining whether the super-Poissonian noise occurs in the weak inter-dot hopping coupling regime depending on the corresponding QD-lead coupling, and the corresponding values of super-Poissonian noise can be relatively enhanced when considering the spins of conduction electrons. Moreover, this super-Poissonian noise bias range depends on the singly-occupied eigenstates of the system, which thus suggests a tunable super-Poissonian noise device. The occurrence-mechanism of super-Poissonian noise can be understood in terms of the interplay of quantum coherence and effective competition between fast-and-slow transport channels. -- Highlights: •The FCS can be used to probe the quantum coherence of side-coupled double QD system. •Probing quantum coherence using FCS may permit experimental tests in the near future. •The current noise characteristics depend on the quantum coherence of this QD system. •The super-Poissonian noise can be enhanced when considering conduction electron spin. •The side-coupled double QD system suggests a tunable super-Poissonian noise device.

  4. Probing the structural dependency of photoinduced properties of colloidal quantum dots using metal-oxide photo-active substrates

    SciTech Connect (OSTI)

    Patty, Kira; Campbell, Quinn; Hamilton, Nathan; West, Robert G. [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Sadeghi, Seyed M., E-mail: seyed.sadeghi@uah.edu [Department of Physics, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Nano and Micro Device Center, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States); Mao, Chuanbin [Department of Chemistry and Biochemistry, Stephenson Life Sciences Research Center, University of Oklahoma, Norman, Oklahoma 73019 (United States)

    2014-09-21T23:59:59.000Z

    We used photoactive substrates consisting of about 1 nm coating of a metal oxide on glass substrates to investigate the impact of the structures of colloidal quantum dots on their photophysical and photochemical properties. We showed during irradiation these substrates can interact uniquely with such quantum dots, inducing distinct forms of photo-induced processes when they have different cores, shells, or ligands. In particular, our results showed that for certain types of core-shell quantum dot structures an ultrathin layer of a metal oxide can reduce suppression of quantum efficiency of the quantum dots happening when they undergo extensive photo-oxidation. This suggests the possibility of shrinking the sizes of quantum dots without significant enhancement of their non-radiative decay rates. We show that such quantum dots are not influenced significantly by Coulomb blockade or photoionization, while those without a shell can undergo a large amount of photo-induced fluorescence enhancement via such blockade when they are in touch with the metal oxide.

  5. Non-adiabatic quantum pumping by a randomly moving quantum dot

    E-Print Network [OSTI]

    Stanislav Derevyanko; Daniel Waltner

    2015-02-10T23:59:59.000Z

    We look at random time dependent fluctuations of the electrical charge in an open 1D quantum system represented by a quantum dot experiencing random lateral motion. In essentially non-adiabatic settings we study both diffusive and ballistic (Levy) regimes of the barrier motion. Here the electric current as well as the net pumped electric charge experience random fluctuations over the static background. We show that in the large-time limit $t \\to \\infty$ the wavefunction is naturally separated into the Berry-phase component (resulting from the singular part of the wave amplitude in the co-moving frame) and the non-adiabatic correction (arising from fast oscillating, slow decaying tails of the same amplitude). In the special limit of a delta-correlated continuous Gaussian random walk we obtain closed analytical expressions for the ensemble averaged amplitude in the co-moving frame and demonstrate that the main contribution to the average wavefunction and probability current comes from the Berry-phase component which leads to the saturation of the fluctuations of the electric current and the pumped charge. We also derive the exact expressions for the average propagator (in the co-moving basis representation) for both types of motion.

  6. Analysis of InAs/GaAs quantum dot solar cells using Suns-Voc measurements

    E-Print Network [OSTI]

    Beattie, N. S.; Zoppi, G.; See, P.; Farrer, I.; Duchamp, M.; Morrison, D. J.; Miles, R. W.; Ritchie, D. A.

    2014-08-06T23:59:59.000Z

    . Appl. Phys. 32 (1961) 510. [10] G. Wei, K. Shiu, N.C. Giebink, S.R. Forrest, Thermodynamic limits of quantum photovoltaic cell efficiency, Appl. Phys. Lett. 91 (2007) 223507. [11] A. Martí, A. Luque, Comment on Thermodynamics limits of quantum photo... /GaAs quantum dot solar cells and the influence on the open circuit voltage, Appl. Phys. Lett. 97 (2010) 123505. [26] A. Martí, A. Luque, Next Generation Photovoltaics: High Efficiency Through Full Spectrum Utilization, IOP Publishing, Bristol, UK, 2004. [27] H...

  7. Role of surface states and defects in the ultrafast nonlinear optical properties of CuS quantum dots

    SciTech Connect (OSTI)

    Mary, K. A. Ann; Unnikrishnan, N. V., E-mail: nvu100@yahoo.com [School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam 686560 (India); Philip, Reji [Light and Matter Physics Group, Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore 560080 (India)

    2014-07-01T23:59:59.000Z

    We report facile preparation of water dispersible CuS quantum dots (2–4 nm) and nanoparticles (5–11 nm) through a nontoxic, green, one-pot synthesis method. Optical and microstructural studies indicate the presence of surface states and defects (dislocations, stacking faults, and twins) in the quantum dots. The smaller crystallite size and quantum dot formation have significant effects on the high energy excitonic and low energy plasmonic absorption bands. Effective two-photon absorption coefficients measured using 100 fs laser pulses employing open-aperture Z-scan in the plasmonic region of 800 nm reveal that CuS quantum dots are better ultrafast optical limiters compared to CuS nanoparticles.

  8. Spin and Conductance-Peak-Spacing Distributions in Large Quantum Dots: A Density-Functional Theory Study

    E-Print Network [OSTI]

    Baranger, Harold U.

    of solid-state physics. A semiconductor quantum dot (QD) [1,2]--a nanodevice in which electron motion was regu- lar in shape [24]. Our aim here is to bridge the gap between the two theoretical approaches

  9. High Throughput Synthesis of Uniform Biocompatible Polymer Beads with High Quantum Dot Loading Using Microfluidic Jet-Mode Breakup

    E-Print Network [OSTI]

    Lee, Seung-Kon

    Uniform polymer microbeads with highly loaded quantum dots (QDs) are produced using high-throughput coherent jet breakup of a biocompatible poly(ethylene glycol) diacrylate (PEGDA) prepolymer resin, followed by in-line ...

  10. Hole Spin Pumping and Re-pumping in a p-type ?-doped InAs Quantum Dot

    E-Print Network [OSTI]

    Konstantinos G. Lagoudakis; Kevin A. Fischer; Tomas Sarmiento; Kai Mueller; Jelena Vu?kovi?

    2014-08-29T23:59:59.000Z

    We have grown high quality p-type {\\delta}-doped InAs quantum dots and have demonstrated coherent spin pumping and repumping of a hole spin in a positively charged quantum dot by means of a single-laser driving scheme under a high magnetic field in the Voigt configuration. Modeling of our system shows excellent qualitative agreement with the experimental findings and further explores the performance of the single-laser scheme for spin pumping and re-pumping.

  11. Establishment of correlated states in a quantum dot interacting with an acoustic phonon reservoir

    E-Print Network [OSTI]

    Hui Huang; Gao-xiang Li; Wen-ju Gu; Zbigniew Ficek

    2014-08-20T23:59:59.000Z

    We investigate the effects of a low frequency (acoustic) phonon bath on the dynamics of a quantum dot modelled as a cascade three-level system. We show that the phonon bath appears to the upper transition of the cascade system as a broadband reservoir of inverted rather than conventional harmonic oscillators. The action of the annihilation and creation operators of the inverted oscillator are interchanges relative to those of the usual harmonic oscillator that it serves as a linear amplifier to the system, and thereby gives rise to unusual features in the dynamics of the quantum dot. We find that the phonon bath, although being in a thermal state, affects the quantum dot as a correlated-type reservoir which results in the decay of the system to a correlated two-photon state with the population distribution no longer obeying a Boltzmann distribution. It is particularly interesting that even for a zero temperature phonon reservoir the steady state is a correlated state which under appropriate conditions on the Rabi frequencies and the damping rates can reduce to a strongly correlated pure state. It is shown that the two-photon correlations result in a significant squeezing and strong two-photon correlations in the radiation field emitted by the quantum dot. The presence of the correlations in the system is manifest in the presence of quantum beats in the time evolution of the populations and the radiation intensity. The effect of the ordinary spontaneous emission on the features induced by the phonon bath is also discussed.

  12. Monolithic phosphor-free InGaN/GaN quantum dot wavelength converter white light emitting diodes

    SciTech Connect (OSTI)

    Jahangir, Shafat; Bhattacharya, Pallab, E-mail: pkb@eecs.umich.edu [Center for Photonics and Multiscale Nanomaterials, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States); Pietzonka, Ines; Strassburg, Martin [OSRAM Opto Semiconductors GmbH, Leibnizstrasse 4, Regensburg (Germany)

    2014-09-15T23:59:59.000Z

    We report the characteristics of phosphor-free self-organized InGaN/GaN quantum dot wavelength converter white light emitting diodes grown by plasma assisted molecular beam epitaxy. The exciting quantum dots, in which electrically injected carriers recombine, are blue-emitting and the converter dots are red-emitting. We have studied the effect of tuning the number of dot layers and the peak emission wavelength of the exciting and converter dots on the nature of the emitted white light, in terms of the chromaticity coordinates and correlated color temperature. Depending on the values of these wavelengths, color temperatures in the range of 4420–6700?K have been derived at a current density of 45?A/cm{sup 2} across multiple devices. The variation of the color temperature with change in injection current is found to be very small.

  13. Thermoelectric infrared microsensors based on a periodically suspended thermopile integrating nanostructured Ge/SiGe quantum dots superlattice

    SciTech Connect (OSTI)

    Ziouche, K., E-mail: katir.ziouche@iemn.univ-lille1.fr, E-mail: Zahia.bougrioua@iemn.univ-lille1.fr; Bougrioua, Z., E-mail: katir.ziouche@iemn.univ-lille1.fr, E-mail: Zahia.bougrioua@iemn.univ-lille1.fr; Lejeune, P.; Lasri, T.; Leclercq, D. [IEMN, Institute of Electronics, Microelectronics and Nanotechnology, CNRS and Lille 1 University, F-59652 Villeneuve d'Ascq (France); Savelli, G.; Hauser, D.; Michon, P.-M. [CEA, LITEN, Thermoelectricity Laboratory, F-38054 Grenoble (France)

    2014-07-28T23:59:59.000Z

    This paper presents an original integration of polycrystalline SiGe-based quantum dots superlattices (QDSL) into Thermoelectric (TE) planar infrared microsensors (?SIR) fabricated using a CMOS technology. The nanostructuration in QDSL results into a considerably reduced thermal conductivity by a factor up to 10 compared to the one of standard polysilicon layers that are usually used for IR sensor applications. A presentation of several TE layers, QDSL and polysilicon, is given before to describe the fabrication of the thermopile-based sensors. The theoretical values of the sensitivity to irradiance of ?SIR can be predicted thanks to an analytical model. These findings are used to interpret the experimental measurements versus the nature of the TE layer exploited in the devices. The use of nanostructured QDSL as the main material in ?SIR thermopile has brought a sensitivity improvement of about 28% consistent with theoretical predictions. The impact of QDSL low thermal conductivity is damped by the contribution of the thermal conductivity of all the other sub-layers that build up the device.

  14. Spectrum of surface plasmons excited by spontaneous quantum dot transitions

    SciTech Connect (OSTI)

    Andrianov, E. S., E-mail: andrianov.es@mipt.ru; Pukhov, A. A., E-mail: pukhov@mail.ru; Dorofeenko, A. V.; Vinogradov, A. P. [Russian Academy of Sciences, Institute of Theoretical and Applied Electrodynamics (Russian Federation)] [Russian Academy of Sciences, Institute of Theoretical and Applied Electrodynamics (Russian Federation); Lisyansky, A. A. [Queens College of the City University of New York, Department of Physics (United States)] [Queens College of the City University of New York, Department of Physics (United States)

    2013-08-15T23:59:59.000Z

    We consider quantum fluctuations of near fields of a quantum emitter (two-level system (TLS) with population inversion sustained by incoherent pumping) in the near-field zone of a plasmon (metallic) nanoparticle. The spectrum of surface plasmons excited by spontaneous transitions in the quantum emitter is obtained below the lasing threshold of such a system (spaser) in the approximation of a small number of plasmons. It is shown that the relaxation rate is the sum of the quantum emitter's rates of relaxation to its thermal reservoir and the plasmon cavity. The resulting dependence of the average number of plasmons on the pump intensity indicates the nonthreshold nature of the process.

  15. Fast and efficient single electron transfer between distant quantum dots S. Hermelin, S. Takada, M. Yamamoto, S. Tarucha, A. D. Wieck et al.

    E-Print Network [OSTI]

    Paris-Sud XI, Université de

    Cooperative Research Project) Quantum Spin Information Project, Atsugi-shi, Kanagawa 243-0198, Japan 5 to manipulate a single electron or its spin quantum coherently.1­5 In addition, double dots--i.e., two dots thanks to surface-acoustic-wave assisted transport. In the context of quantum computing, displaced

  16. Carrier transfer from InAs quantum dots to ErAs metal nanoparticles

    SciTech Connect (OSTI)

    Haughn, C. R.; Chen, E. Y.; Zide, J. M. O.; Doty, M. F., E-mail: doty@udel.edu [Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716 (United States); Steenbergen, E. H.; Bissell, L. J.; Eyink, K. G. [AFRL/RXAN, Wright Patterson AFB, Ohio 45433 (United States)

    2014-09-08T23:59:59.000Z

    Erbium arsenide (ErAs) is a semi-metallic material that self-assembles into nanoparticles when grown in GaAs via molecular beam epitaxy. We use steady-state and time-resolved photoluminescence to examine the mechanism of carrier transfer between indium arsenide (InAs) quantum dots and ErAs nanoparticles in a GaAs host. We probe the electronic structure of the ErAs metal nanoparticles (MNPs) and the optoelectronic properties of the nanocomposite and show that the carrier transfer rates are independent of pump intensity. This result suggests that the ErAs MNPs have a continuous density of states and effectively act as traps. The absence of a temperature dependence tells us that carrier transfer from the InAs quantum dots to ErAs MNPs is not phonon assisted. We show that the measured photoluminescence decay rates are consistent with a carrier tunneling model.

  17. Coherent Optical Spectroscopy of a Single Quantum Dot Via an Off-Resonant Cavity

    E-Print Network [OSTI]

    Arka Majumda; Alexander Papageorge; Erik D. Kim; Michal Bajscy; Hyochul Kim; Pierre Petroff; Jelena Vuckovic

    2011-03-14T23:59:59.000Z

    In recent experiments on coupled quantum dot (QD) optical cavity systems a pronounced interaction between the dot and the cavity has been observed even for detunings of many cavity linewidths. This interaction has been attributed to an incoherent phonon-mediated scattering process and is absent in atomic systems. Here, we demonstrate that despite its incoherent nature, this process preserves the signatures of coherent interaction between a QD and a strong driving laser, which may be observed via the optical emission from the off-resonant cavity. Under bichromatic driving of the QD, the cavity emission exhibits spectral features consistent with optical dressing of the QD transition. In addition to revealing new aspects of the off-resonant QD-cavity interaction, this result provides a new, simpler means of coherently probing QDs than traditional approaches and opens the possibility of employing off-resonant cavities to optically interface QD-nodes in quantum networks.

  18. Enhanced single-photon emission from a quantum dot in a micropost microcavity

    E-Print Network [OSTI]

    Jelena Vuckovic; David Fattal; Charles Santori; Glenn Solomon; Yoshihisa Yamamoto

    2003-07-03T23:59:59.000Z

    We demonstrate a single-photon source based on a quantum dot in a micropost microcavity that exhibits a large Purcell factor together with a small multi-photon probability. For a quantum dot on resonance with the cavity, the spontaneous emission rate is increased by a factor of five, while the probability to emit two or more photons in the same pulse is reduced to 2% compared to a Poisson-distributed source of the same intensity. In addition to the small multi-photon probability, such a strong Purcell effect is important in a single-photon source for improving the photon outcoupling efficiency and the single-photon generation rate, and for bringing the emitted photon pulses closer to the Fourier transform limit.

  19. All-electrical single-electron shuttle in a silicon quantum dot

    E-Print Network [OSTI]

    Chan, K W; Kemppinen, A; Lai, N S; Tan, K Y; Lim, W H; Dzurak, A S

    2011-01-01T23:59:59.000Z

    We report on single-electron shuttling experiments with a silicon metal-oxide-semiconductor quantum dot at 300 mK. Our system consists of an accumulated electron layer at the Si/SiO2 interface below an aluminum top gate with two additional barrier gates used to deplete the electron gas locally and to define a quantum dot. Directional single-electron shuttling from the source and to the drain lead is achieved by applying a dc source-drain bias while driving the barrier gates with an ac voltage of frequency fp. Current plateaus at integer levels of efp are observed up to fp = 240 MHz operation frequencies. The observed results are explained by a sequential tunneling model which suggests that the electron gas may be heated substantially by the ac driving voltage.

  20. Synthesis of Non-blinking Semiconductor Quantum Dots Emitting in the Near-Infrared

    SciTech Connect (OSTI)

    Dennis, Allison M. [Los Alamos National Laboratory; Mangum, Benjamin D. [Los Alamos National Laboratory; Piryatinski, Andrei [Los Alamos National Laboratory; Park, Young-Shin [Los Alamos National Laboratory; Htoon, Han [Los Alamos National Laboratory; Hollingsworth, Jennifer A. [Los Alamos National Laboratory

    2012-06-21T23:59:59.000Z

    Our previous work demonstrates that Quasi-Type II CdSe/CdS core-shell quantum dots with thick shells (3-5 nm) exhibit unique photophysical characteristics, including improved chemical robustness over typical thin-shelled core/shell systems and the elimination of blinking through suppression of nonradiative Auger recombination. Here we describe a new thick-shelled heterostructure, InP/CdS, which exhibits a Type II bandgap alignment producing near-infrared (NIR) emission. Samples with a range of shell thicknesses were synthesized, enabling shell-thickness-dependent study of the absorbance and emission spectra, fluorescence lifetimes, and quantum yields. InP/CdS/ZnS core/shell/shell structures were also synthesized to reduce cadmium exposure for applications in the biological environment. Single particle spectroscopy indicates reduced blinking and improved photostability with increasing shell thickness, resulting in thick-shelled dots that are appropriate for single-particle tracking measurements with NIR emission.

  1. Quantum dot nonlinearity through cavity-enhanced feedback with a charge memory

    E-Print Network [OSTI]

    Morten P. Bakker; Thomas Ruytenberg; Wolfgang Loffler; Ajit V. Barve; Larry Coldren; Martin P. van Exter; Dirk Bouwmeester

    2015-03-27T23:59:59.000Z

    In an oxide apertured quantum dot (QD) micropillar cavity-QED system, we found strong QD hysteresis effects and lineshape modifications even at very low intensities corresponding to less than 0.001 intracavity photons. We attribute this to the excitation of charges by the intracavity field; charges that get trapped at the oxide aperture, where they screen the internal electric field and blueshift the QD transition. This in turn strongly modulates light absorption by cavity QED effects, eventually leading to the observed hysteresis and lineshape modifications. The cavity also enables us to observe the QD dynamics in real time, and all experimental data agrees well with a power-law charging model. This effect can serve as a novel tuning mechanism for quantum dots.

  2. Phonon-assisted robust and deterministic two-photon biexciton preparation in a quantum dot

    E-Print Network [OSTI]

    S. Bounouar; M. Müller; A. M. Barth; M. Glässl; V. M. Axt; P. Michler

    2014-08-29T23:59:59.000Z

    We investigate both experimentally and theoretically a simple yet more robust and flexible alternative to Rabi oscillation-type biexciton preparation protocols traditionally used for semiconductor quantum dots. The quantum dot is excited by a strong laser pulse positively detuned from the two-photon resonance yielding an on demand initialization of the biexciton state by making use of the phonon-induced thermalization of the photon dressed states. It is shown that for excitation pulses in the picosecond range, a stable and high fidelity of up to $f_{XX}=0.98\\pm 0.01$ is reached. Notably, the generated photons show similar coherence properties as measured in the resonant two-photon scheme. This protocol is a powerful tool for the control of complex solid state systems combining radiative cascades, entanglement and resonant cavity modes.

  3. SiGe/sSi quantum dot electron spin decoherence dependence on $^{73}$Ge

    E-Print Network [OSTI]

    Witzel, Wayne M; Carroll, Malcolm S

    2011-01-01T23:59:59.000Z

    We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on $^{73}$Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-binding modeling for an accurate account of the electron wavefunction which is particularly important for determining the contact hyperfine interactions with the Ge nuclear spins. We find decoherence times due to Ge spins at natural concentrations to be milliseconds. This suggests SiGe/sSi quantum dot devices employing enriched Si will require enriched Ge as well in order to benefit from long coherence times. We provide a comparison of $T_2$ times for various fractions of nonzero spin isotopes of Si and Ge.

  4. SiGe/Si quantum dot electron spin decoherence dependence on $^{73}$Ge

    E-Print Network [OSTI]

    Wayne M. Witzel; Rajib Rahman; Malcolm S. Carroll

    2012-05-14T23:59:59.000Z

    We theoretically study the nuclear spin induced decoherence of a quantum dot in Si that is confined at a SiGe interface. We calculate decoherence time dependence on $^{73}$Ge in the barrier layer to evaluate the importance of Ge as well as Si enrichment for long decoherence times. We use atomistic tight-binding modeling for an accurate account of the electron wavefunction which is particularly important for determining the contact hyperfine interactions with the Ge nuclear spins. We find decoherence times due to Ge spins at natural concentrations to be milliseconds. This suggests SiGe/Si quantum dot devices employing enriched Si will require enriched Ge as well in order to benefit from long coherence times. We provide a comparison of $T_2$ times for various fractions of nonzero spin isotopes of Si and Ge.

  5. Decision making based on optical excitation transfer via near-field interactions between quantum dots

    SciTech Connect (OSTI)

    Naruse, Makoto, E-mail: naruse@nict.go.jp [Photonic Network Research Institute, National Institute of Information and Communications Technology, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795 (Japan); Nomura, Wataru; Ohtsu, Motoichi [Department of Electrical Engineering and Information Systems, Graduate School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Aono, Masashi [Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguru-ku, Tokyo 152-8550 (Japan); PRESTO, Japan Science and Technology Agency, 4-1-8 Honcho, Kawaguchi-shi, Saitama 332-0012 (Japan); Sonnefraud, Yannick; Drezet, Aurélien; Huant, Serge [Université Grenoble Alpes, Inst. NEEL, F-38000 Grenoble (France); CNRS, Inst. NEEL, F-38042 Grenoble (France); Kim, Song-Ju [WPI Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan)

    2014-10-21T23:59:59.000Z

    Optical near-field interactions between nanostructured matters, such as quantum dots, result in unidirectional optical excitation transfer when energy dissipation is induced. This results in versatile spatiotemporal dynamics of the optical excitation, which can be controlled by engineering the dissipation processes and exploited to realize intelligent capabilities such as solution searching and decision making. Here, we experimentally demonstrate the ability to solve a decision making problem on the basis of optical excitation transfer via near-field interactions by using colloidal quantum dots of different sizes, formed on a geometry-controlled substrate. We characterize the energy transfer behavior due to multiple control light patterns and experimentally demonstrate the ability to solve the multi-armed bandit problem. Our work makes a decisive step towards the practical design of nanophotonic systems capable of efficient decision making, one of the most important intellectual attributes of the human brain.

  6. Tuning photoluminescence of reduced graphene oxide quantum dots from blue to purple

    SciTech Connect (OSTI)

    Liu, Fuchi [Physics Department and Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China); College of Physics and Technology, Guangxi Normal University, Guilin 541004 (China); Tang, Tao; Feng, Qian; Li, Ming; Liu, Yuan; Tang, Nujiang, E-mail: tangnujiang@nju.edu.cn; Zhong, Wei; Du, Youwei [Physics Department and Nanjing National Laboratory of Microstructures, Nanjing University, Nanjing 210093 (China)

    2014-04-28T23:59:59.000Z

    Reduced graphene oxide quantum dots (rGOQDs) were synthesized by annealing GOQDs in H{sub 2} atmosphere. The photoluminescence (PL) properties of GOQDs and the rGOQDs samples were investigated. The results showed that compared to GOQDs, a blue to purple tunable PL of rGOQDs can be obtained by regulating the annealing temperature. The increase fraction of the newly formed isolated sp{sup 2} clusters may be responsible for the observed tunable PL.

  7. Probing the ladder of dressed states and nonclassical light generation in quantum dot-cavity QED

    E-Print Network [OSTI]

    Arka Majumdar; Michal Bajcsy; Jelena Vuckovic

    2011-10-21T23:59:59.000Z

    We investigate the photon induced tunneling phenomena in a photonic crystal cavity containing a strongly coupled quantum dot and describe how this tunneling can be used to generate photon states consisting mainly of a particular Fock state. Additionally, we study experimentally the photon-induced tunneling as a function of excitation laser power and frequency and show the signature of second rung of the Jaynes-Cummings Hamiltonian in the observed photon-statistics.

  8. Observations of Rabi oscillations in a non-polar InGaN quantum dot

    SciTech Connect (OSTI)

    Reid, Benjamin P. L., E-mail: benjamin.reid@physics.ox.ac.uk; Chan, Christopher C. S.; Taylor, Robert A. [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Kocher, Claudius [Department of Physics, University of Oxford, Parks Road, Oxford OX1 3PU (United Kingdom); Konstanz University, Konstanz (Germany); Zhu, Tongtong; Oehler, Fabrice; Emery, Robert; Oliver, Rachel A. [Department of Materials Science and Metallurgy, 27 Charles Babbage Road, Cambridge CB3 0FS (United Kingdom)

    2014-06-30T23:59:59.000Z

    Experimental observation of Rabi rotations between an exciton excited state and the crystal ground state in a single non-polar InGaN quantum dot is presented. The exciton excited state energy is determined by photoluminescence excitation spectroscopy using two-photon excitation from a pulsed laser. The population of the exciton excited state is seen to undergo power dependent damped Rabi oscillations.

  9. Brightly photoluminescent phosphor materials based on silicon quantum dots with oxide shell

    E-Print Network [OSTI]

    Cao, Guozhong

    .-J. Cheng, Y. Tian, M. S. Liu, J. Zhao, J. A. Bardecker, I. J.-L. Plante, D. S. Ginger, and A. K.-Y. Jen for display backlights," Adv. Mater. (Deerfield Beach Fla.) 22(28), 3076­3080 (2010). 9. Z. Ding, B. M. Quinn quantum dot-organic light-emitting diodes," Appl. Phys. Lett. 98(21), 213102 (2011). 11. K.-Y. Cheng, R

  10. Second harmonic generation from direct band gap quantum dots pumped by femtosecond laser pulses

    SciTech Connect (OSTI)

    Liu, Liwei, E-mail: liulw@cust.edu.cn; Wang, Yue; Hu, Siyi; Ren, Yu; Huang, Chen [School of Science, Changchun University of Science and Technology, Changchun, Jilin 130022, People's Republic of China and International Joint Research Center for Nanophotonics and Biophotonics, Changchun University of Science and Technology, Changchun, Jilin 130022 (China)

    2014-02-21T23:59:59.000Z

    We report on nonlinear optical experiments performed on Cu{sub 2}S quantum dots (QDs) pumped by femtosecond laser pulses. We conduct a theoretical simulation and experiments to determine their second harmonic generation characteristics. Furthermore, we demonstrate that the QDs have a second harmonic generation conversion efficiency of up to 76%. Our studies suggest that these Cu{sub 2}S QDs can be used for solar cells, bioimaging, biosensing, and electric detection.

  11. Valley splitting in Si quantum dots embedded in SiGe S. Srinivasan,1,2

    E-Print Network [OSTI]

    Rokhinson, Leonid

    Valley splitting in Si quantum dots embedded in SiGe S. Srinivasan,1,2 G. Klimeck,1,2 and L. P subband.4 Recently, calculations predicted that valley splitting in nar- row few nanometers SiGe/Si/SiGe that prediction, which has been explained12 by the disorders of the Si/SiGe interface and in the SiGe buffer

  12. Spectral properties of a hybrid-qubit model based on a two-dimensional quantum dot

    E-Print Network [OSTI]

    Alba Y. Ramos; Omar Osenda

    2015-03-27T23:59:59.000Z

    The design and study of hybrid qubits is driven by their ability to get along the best of charge qubits and of spin qubits, {\\em i.e.} the speed of operation of the former and the very slow decoherence rates of the latter ones. There are several proposals to implement hybrid qubits, this works focuses on the spectral properties of an one-electron hybrid qubit. By design, the information would be stored in the electronic spin and the switching between the qubit basis states would be achieved using an external ac electric field. The electron is confined in a two-dimensional quantum dot, whose confining potential is given by a quartic potential, features that are typical of GaAS quantum dots. Besides the confining potential that characterizes the quantum dot there are two static magnetic fields applied to the system, one is a large constant Zeeman field and the other one has a constant gradient. We study the spectral properties of the model Hamiltonian, a Scr\\"odinger-Pauli Hamiltonian with realistic parameters, using the Ritz method. In particular, we look for regions of the parameter space where the lowest eigenenergies and their eigenfunctions allow to define a qubit which is stable under perturbations to the design parameters. We put special attention to the constraints that the design imposes over the magnetic fields, the tuning of the energy gap between the qubit states and the expectation value of the spin operator where the information would be stored.

  13. Heat induced nanoforms of zinc oxide quantum dots and their characterization

    SciTech Connect (OSTI)

    Dey, Anindita [Jadavpur University, Physics Department (India); Basu, Ruma [Jogamaya Devi College, Physics department (India); Das, Sukhen, E-mail: sukhendasju@gmail.com; Nandy, Papiya [Jadavpur University, Physics Department (India)

    2012-02-15T23:59:59.000Z

    In our studies we observed heat induced phase transitions of Zinc oxide quantum dots at 60, 200, 360 and 400 Degree-Sign C, where all the transitions were irreversible except the transition at 60 Degree-Sign C which wasa reversible one. The phase transition at 60 Degree-Sign C indicated a heat induced conformational change which was supported here by studying polarizing micrographs of ZnO quantum dots thin film. The X-ray diffraction studies of the sample fired at different temperatures as indicated by the thermal analysis were performed in order to understand the changes occurred due to transitions. The study also indicated a new and simple approach to develop ZnO nanorods by just thermal decomposition of the ZnO quantum dots firing in furnace at 200 Degree-Sign C with 2h soaking. In order to have a proper insight of the structural changes we performed scanning electron microscopy. Optical characterization was done by UV-Vis and fluorescence spectrophotometer.

  14. Photoconductivity of structures based on the SnO{sub 2} porous matrix coupled with core-shell CdSe/CdS quantum dots

    SciTech Connect (OSTI)

    Drozdov, K. A.; Kochnev, V. I.; Dobrovolsky, A. A.; Khokhlov, D. R. [Department of Physics, Moscow State University, 119991 Moscow (Russian Federation)] [Department of Physics, Moscow State University, 119991 Moscow (Russian Federation); Popelo, A. V. [Department of Materials Science, Moscow State University, 119991 Moscow (Russian Federation)] [Department of Materials Science, Moscow State University, 119991 Moscow (Russian Federation); Rumyantseva, M. N.; Gaskov, A. M.; Ryabova, L. I. [Department of Chemistry, Moscow State University, 119991 Moscow (Russian Federation)] [Department of Chemistry, Moscow State University, 119991 Moscow (Russian Federation); Vasiliev, R. B. [Department of Materials Science, Moscow State University, 119991 Moscow (Russian Federation) [Department of Materials Science, Moscow State University, 119991 Moscow (Russian Federation); Department of Chemistry, Moscow State University, 119991 Moscow (Russian Federation)

    2013-09-23T23:59:59.000Z

    Embedding of quantum dots into porous oxide matrixes is a perspective technique for photosensitization of a structure. We show that the sensitization efficiency may be increased by the use of core-shell quantum dots. It is demonstrated that the photoresponse amplitude in a SnO{sub 2} porous matrix with CdSe/CdS quantum dots depends non-monotonously on the number of atomic layers in a shell. The best results are obtained for SnO{sub 2} matrixes coupled with the quantum dots with three atomic layers of a shell. Mechanisms responsible for the structure sensitization are discussed.

  15. An intentionally positioned (In,Ga)As quantum dot in a micron sized light emitting diode

    SciTech Connect (OSTI)

    Mehta, M.; Michaelis de Vasconcellos, S.; Zrenner, A.; Meier, C. [Department of Physics and Center for Optoelectronics and Photonics Paderborn (CeOPP), University of Paderborn, Warburger Street 100, 33098 Paderborn (Germany); Reuter, D.; Wieck, A. D. [Applied Solid State Physics, Ruhr-University of Bochum, Universitaetsstr. 150, 44780 Bochum (Germany)

    2010-10-04T23:59:59.000Z

    We have integrated individual (In,Ga)As quantum dots (QDs) using site-controlled molecular beam epitaxial growth into the intrinsic region of a p-i-n junction diode. This is achieved using an in situ combination of focused ion beam prepatterning, annealing, and overgrowth, resulting in arrays of individually electrically addressable (In,Ga)As QDs with full control on the lateral position. Using microelectroluminescence spectroscopy we demonstrate that these QDs have the same optical quality as optically pumped Stranski-Krastanov QDs with random nucleation located in proximity to a doped interface. The results suggest that this technique is scalable and highly interesting for different applications in quantum devices.

  16. Nonlinear Temporal Dynamics of Strongly Coupled Quantum Dot-Cavity System

    E-Print Network [OSTI]

    Arka Majumdar; Dirk Englund; Michal Bajcsy; Jelena Vuckovic

    2011-10-20T23:59:59.000Z

    We theoretically analyze and simulate the temporal dynamics of strongly coupled quantum dot-cavity system driven by a resonant laser pulse. We observe the signature of Rabi oscillation in the time resolved response of the system (i.e., in the numerically calculated cavity output), derive simplified linear and non-linear semi-classical models that approximate well the system's behavior in the limits of high and low power drive pulse, and describe the role of quantum coherence in the exact dynamics of the system. Finally, we also present experimental data showing the signature of the Rabi oscillation in time domain.

  17. Semiconductor quantum dots enhanced graphene/CdTe heterostructure solar cells by photo-induced doping

    E-Print Network [OSTI]

    Li, Xiaoqiang; Wang, Peng; Xu, Zhijuan; Zhong, Huikai; Wu, Zhiqian; Lin, Shisheng

    2015-01-01T23:59:59.000Z

    Photo-induced doping is employed into graphene based solar cell through designing of a novel type of solar cell based on graphene/CdTe Schottky heterostructure. By coating a layer of ultrathin CdSe quantum dots onto graphene/CdTe heterostructure, the performance of the graphene/CdTe solar cell is improved by about 50%. Photo-induced doping is mainly accounted for this enhancement, as evidenced by resistance, photoluminescence and quantum efficiency measurements. This work demonstrates a general and feasible way of designing novel type of solar cells based on two dimensional materials/semiconductor heterostructures.

  18. Nonlocal biphoton generation in Werner state from a single semiconductor quantum dot

    E-Print Network [OSTI]

    H. Kumano; H. Nakajima; T. Kuroda; T. Mano; K. Sakoda; I. Suemune

    2014-08-01T23:59:59.000Z

    We demonstrate Werner-like polarization-entangled state generation disapproving local hidden variable theory from a single semiconductor quantum dot. By exploiting tomographic analysis with temporal gating, we find biphoton states are mapped on the Werner state, which is crucial for quantum information applications due to its versatile ramifications such as usefulness to teleportation. Observed time evolution of the biphoton state brings us systematic understanding on a relationship between tomographically reconstructed biphoton state and a set of parameters characterizing exciton state including fine-structure splitting and cross-dephasing time.

  19. Microchemical systems for the synthesis of nanostructures : quantum dots

    E-Print Network [OSTI]

    Baek, Jinyoung

    2012-01-01T23:59:59.000Z

    We have developed a continuous multi-stage high-temperature and high-pressure microfluidic system. High-pressure conditions enabled the use low molecular weight solvents that have previously not been available for quantum ...

  20. Magnetic relaxation of superconducting quantum dot: two-dimensional false vacuum decay

    E-Print Network [OSTI]

    D. R. Gulevich; F. V. Kusmartsev

    2006-09-11T23:59:59.000Z

    Quantum tunneling of vortices has been found to be an important novel phenomena for description of low temperature creep in high temperature superconductors (HTSCs). We speculate that quantum tunneling may be also exhibited in mesoscopic superconductors due to vortices trapped by the Bean-Livingston barrier. The London approximation and method of images is used to estimate the shape of the potential well in superconducting HTSC quantum dot. To calculate the escape rate we use the instanton technique. We model the vortex by a quantum particle tunneling from a two-dimensional ground state under magnetic field applied in the transverse direction. The resulting decay rates obtained by the instanton approach and conventional WKB are compared revealing complete coincidence with each other.

  1. Semiconductor quantum dots used in so-called"third-generation"solar cells have the potential to dramatically increase--in some cases even double--the efficiency of converting sunlight

    E-Print Network [OSTI]

    innovati n Semiconductor quantum dots used in so-called"third-generation"solar cells have quantum dots (QDs). These semiconductor nanocrystals typically have diameters from about 2 to 10

  2. Near-Infrared Localized Surface Plasmon Resonances Arising from Free Carriers in Doped Quantum Dots

    SciTech Connect (OSTI)

    Jain, Prashant K.; Luther, Joey; Ewers, Trevor; Alivisatos, A. Paul

    2010-10-12T23:59:59.000Z

    Quantum confinement of electronic wavefunctions in semiconductor quantum dots (QDs) yields discrete atom-like and tunable electronic levels, thereby allowing the engineering of excitation and emission spectra. Metal nanoparticles, on the other hand, display strong resonant interactions with light from localized surface plasmon resonance (LSPR) oscillations of free carriers, resulting in enhanced and geometrically tunable absorption and scattering resonances. The complementary attributes of these nanostructures lends strong interest toward integration into hybrid nanostructures to explore enhanced properties or the emergence of unique attributes arising from their interaction. However, the physicochemical interface between the two components can be limiting for energy transfer and synergistic coupling within such a hybrid nanostructure. Therefore, it is advantageous to realize both attributes, i.e., LSPRs and quantum confinement within the same nanostructure. Here, we describe well-defined LSPRs arising from p-type carriers in vacancy-doped semiconductor quantum dots. This opens up possibilities for light harvesting, non-linear optics, optical sensing and manipulation of solid-state processes in single nanocrystals.

  3. Height stabilization of GaSb/GaAs quantum dots by Al-rich capping

    SciTech Connect (OSTI)

    Smakman, E. P., E-mail: e.p.smakman@tue.nl; Koenraad, P. M. [Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5612 AZ Eindhoven (Netherlands); DeJarld, M.; Martin, A. J.; Millunchick, J. [Department of Material Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Luengo-Kovac, M.; Sih, V. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2014-09-01T23:59:59.000Z

    GaSb quantum dots (QDs) in a GaAs matrix are investigated with cross-sectional scanning tunneling microscopy (X-STM) and photoluminescence (PL). We observe that Al-rich capping materials prevent destabilization of the nanostructures during the capping stage of the molecular beam epitaxy (MBE) growth process and thus preserves the QD height. However, the strain induced by the absence of destabilization causes many structural defects to appear around the preserved QDs. These defects originate from misfit dislocations near the GaSb/GaAs interface and extend into the capping layer as stacking faults. The lack of a red shift in the QD PL suggests that the preserved dots do not contribute to the emission spectra. We suggest that a better control over the emission wavelength and an increase of the PL intensity is attainable by growing smaller QDs with an Al-rich overgrowth.

  4. Small quantum dots of diluted magnetic III-V semiconductor compound

    E-Print Network [OSTI]

    Pozhar, Liudmila A

    2012-01-01T23:59:59.000Z

    In this chapter quantum many body theoretical methods have been used to study properties of GaAs - and InAs - based, small semiconductor compound quantum dots (QDs) containing manganese or vanadium atoms. Interest to such systems has grown since experimental synthesis of nanoscale magnetic semiconductors, that is, nanoscale semiconductor compounds with enhanced magnetic properties. This enhancement is achieved by several methods, and in particular by doping common semiconductor compounds with some atoms, such as Mn or V. Experimental studies indicate that the electron spin density in the case of thin nanoscale magnetic semiconductor films and QDs may be delocalized. As described in this chapter, quantum many body theory-based, computational synthesis (i.e., virtual synthesis) of tetrahedral symmetry GaAs and InAs small pyramidal QDs doped with sabstitutional Mn or V atoms proves that such QDs are small magnetic molecules that indeed, possess delocalized and polarized electron spin density. Such delocalization...

  5. Transition to Landau levels in graphene quantum dots F. Libisch, 1, * S. Rotter, 1 J. Gttinger, 2 C. Stampfer, 2,3 and J. Burgdrfer 1

    E-Print Network [OSTI]

    Florian, Libisch

    Transition to Landau levels in graphene quantum dots F. Libisch, 1, * S. Rotter, 1 J. Güttinger, 2 investigate the electronic eigenstates of graphene quantum dots of realistic size #up to 80 nm diameter graphene lattice structure, bulk defects, and localization effects at the edges. Key to the understanding

  6. Transition to Landau levels in graphene quantum dots F. Libisch,1,* S. Rotter,1 J. Gttinger,2 C. Stampfer,2,3 and J. Burgdrfer1

    E-Print Network [OSTI]

    Florian, Libisch

    Transition to Landau levels in graphene quantum dots F. Libisch,1,* S. Rotter,1 J. Güttinger,2 C the electronic eigenstates of graphene quantum dots of realistic size up to 80 nm diameter in the presence-level regime at high fields. Details of this transition sensitively depend on the underlying graphene lattice

  7. Influence of Cationic Precursors on CdS Quantum-Dot-Sensitized Solar Cell Prepared by Successive Ionic Layer Adsorption and

    E-Print Network [OSTI]

    Cao, Guozhong

    as 15% was achieved for perovskite-sensitized solar cells.7 As a derivative of dye-sensitized solarInfluence of Cationic Precursors on CdS Quantum-Dot-Sensitized Solar Cell Prepared by Successive (QDs) onto porous oxide films for quantum-dot-sensitized solar cell (QDSC) applications. In this work

  8. Electrostatically defined quantum dots in a Si/SiGe heterostructure This article has been downloaded from IOPscience. Please scroll down to see the full text article.

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    Electrostatically defined quantum dots in a Si/SiGe heterostructure This article has been of Physics Electrostatically defined quantum dots in a Si/SiGe heterostructure A Wild1 , J Sailer1 , J Nützel epitaxially grown Si/SiGe heterostructure. Transport and charge spectroscopy with an additional QD as well

  9. Sandia Energy - Research Challenge 2: Quantum Dots and Phosphors

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative1 First Use of Energy for All Purposes (Fuel and Nonfuel), 2002; Level: National5Sales for4,645 3,625 1,006 492 742EnergyOnItemResearch > TheNuclear PressLaboratory FellowsPolariton LasingQuantum0:1:2:

  10. Fluorescence relaxation dynamics of CdSe and CdSe/CdS core/shell quantum dots

    SciTech Connect (OSTI)

    Kaur, Gurvir; Kaur, Harmandeep [Centre of Advanced Study in Physics, Department of Physics, Panjab University, Chandigarh-160014 (India); Tripathi, S. K., E-mail: surya@pu.ac.in [Centre of Advanced Study in Physics, Panjab University, Chandigarh- 160014 (India)

    2014-04-24T23:59:59.000Z

    Time-resolved fluorescence spectra for colloidal CdSe and CdSe/CdS core/shell quantum dots have been investigated to know their electron relaxation dynamics at the maximum steady state fluorescence intensity. CdSe core and CdSe/CdS type I core-shell materials with different shell (CdS) thicknesses have been synthesized using mercaptoacetic acid as a capping agent. Steady state absorption and emission studies confirmed successful synthesis of CdSe and CdSe/CdS core-shell quantum dots. The fluorescence shows a tri-exponential decay with lifetimes 57.39, 7.82 and 0.96 ns for CdSe quantum dots. The lifetime of each recombination decreased with growth of CdS shell over the CdSe core, with maximum contribution to fluorescence by the fastest transition.

  11. Quantum-dot all-optical logic in a structured vacuum

    SciTech Connect (OSTI)

    Ma Xun; John, Sajeev [Department of Physics, University of Toronto, Toronto, M5S 1A7 (Canada)

    2011-07-15T23:59:59.000Z

    We demonstrate multiwavelength channel optical logic operations on the Bloch vector of a quantum two-level system in the structured electromagnetic vacuum of a bimodal photonic crystal waveguide. This arises through a bichromatic strong-coupling effect that enables unprecedented control over single quantum-dot (QD) excitation through two beams of ultrashort femtojoule pulses. The second driving pulse (signal) with slightly different frequency and weaker strength than the first (holding) pulse leads to controllable strong modulation of the QD Bloch vector evolution path. This occurs through resonant coupling of the signal pulse with the Mollow sideband transitions created by the holding pulse. The movement of the Mollow sidebands during the passage of the holding pulse leads to an effective chirping in transition frequency seen by the signal. Bloch vector dynamics in the rotating frame of the signal pulse and within the dressed-state basis created by the holding pulse reveals that this chirped coupling between the signal pulse and the Mollow sidebands leads to either augmentation or negation of the final quantum-dot population (after pulse passage) compared to the outcome of the holding pulse alone and depending on the relative frequencies of the pulses. By making use of this extra degree of freedom for ultrafast control of QD excitations, applications in ultrafast all-optical logic and, or, and not gates are proposed in the presence of significant (0.1) THz nonradiative dephasing and (about 1%) inhomogeneous broadening.

  12. On-chip single photon sources based on quantum dots in photonic crystal structures

    E-Print Network [OSTI]

    Schwagmann, Andre

    2013-02-05T23:59:59.000Z

    of this dissertation have appeared or will appear in form of the following journal articles and contributed talks at international conferences. Articles A. Schwagmann, S. Kalliakos, I. Farrer, J. P. Griffiths, G. A. C. Jones, D. A. Ritchie, and A. J. Shields. “On... -chip single photon emission from an integrated semiconductor quantum dot into a photonic crystal waveguide.” Applied Physics Letters 99, 261108 (2011). A. Schwagmann, S. Kalliakos, D. J. P. Ellis, I. Farrer, J. P. Griffiths, G. A. C. Jones, D. A. Ritchie...

  13. SiGe quantum dots for fast hole spin Rabi oscillations

    SciTech Connect (OSTI)

    Ares, N.; Prager, A.; De Franceschi, S. [SPSMS/LaTEQS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France)] [SPSMS/LaTEQS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Katsaros, G. [SPSMS/LaTEQS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France) [SPSMS/LaTEQS, CEA-INAC/UJF-Grenoble 1, 17 Rue des Martyrs, 38054 Grenoble Cedex 9 (France); Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany); Johannes Kepler University, Institute of Semiconductor and Solid State Physics, Altenbergerstr. 69, 4040 Linz (Austria); Golovach, V. N. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany) [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany); Centro de Física de Materiales CFM/MPC (CSIC-UPV/EHU) and Donostia International Physics Center DIPC, E-20018 San Sebastián (Spain); IKERBASQUE, Basque Foundation for Science, E-48011 Bilbao (Spain); Zhang, J. J. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany)] [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany); Glazman, L. I. [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States)] [Department of Physics, Yale University, New Haven, Connecticut 06520 (United States); Schmidt, O. G. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany) [Institute for Integrative Nanosciences, IFW Dresden, Helmholtzstr. 20, D-01069 Dresden (Germany); Center for Advancing Electronics Dresden, TU Dresden (Germany)

    2013-12-23T23:59:59.000Z

    We report on hole g-factor measurements in three terminal SiGe self-assembled quantum dot devices with a top gate electrode positioned very close to the nanostructure. Measurements of both the perpendicular as well as the parallel g-factor reveal significant changes for a small modulation of the top gate voltage. From the observed modulations, we estimate that, for realistic experimental conditions, hole spins can be electrically manipulated with Rabi frequencies in the order of 100?MHz. This work emphasises the potential of hole-based nano-devices for efficient spin manipulation by means of the g-tensor modulation technique.

  14. Site control technique for quantum dots using electron beam induced deposition

    SciTech Connect (OSTI)

    Iizuka, Kanji; Jung, JaeHun; Yokota, Hiroshi [Nippon Institute of Technology, 4-1 Gakuendai, Miyashiro, Minami-saitama, Saitama 3458501 (Japan)

    2014-05-15T23:59:59.000Z

    To develop simple and high throughput sit definition technique for quantum dots (QDs), the electron beam induced deposition (EBID) method was used as desorption guide of phosphorus atoms form InP substrate. As the results one or a few indium (In) droplets (DLs) were created in the carbon grid pattern by thermal annealing at a temperature of 450°C for 10 min in the ultra high vacuum condition. The size of In DLs was larger than QDs, but arsenide DLs by molecular beam in growth chamber emitted wavelength of 1.028?m at 50K by photoluminescence measurement.

  15. Slow-light propagation using mode locking of spin precession in quantum dots

    SciTech Connect (OSTI)

    Shabaev, A. [George Mason University, Fairfax Virginia 22030 (United States); Dutton, Z. [Raytheon BBN Technologies, 10 Moulton Street, Cambridge, Massachusetts 02138 (United States); Naval Research Laboratory, Washington, D.C. 20375 (United States); Kennedy, T. A.; Efros, Al. L. [Naval Research Laboratory, Washington, D.C. 20375 (United States)

    2010-11-15T23:59:59.000Z

    We propose using mode locking to enable coherent nonlinear optical effects in inhomogenously broadened spin ensembles. We carry out detailed calculations for quantum dot systems in which increased spin coherence via mode locking has been recently observed [A. Greilich et al., Science 313, 341 (2006); 317, 1896 (2007)]. We show how, in the presence of spin locking, a strong pulse-matching effect occurs, providing a powerful tool for high-bandwidth linear optical processing. We then go on to study 'slow light' in this system and show that high-bandwidth pulses can be controllably delayed by a time comparable to the pulse width.

  16. Spectral dependence of the linewidth enhancement factor in quantum dot lasers

    SciTech Connect (OSTI)

    Zubov, F. I., E-mail: fedyazu@mail.ru [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Shernyakov, Yu. M.; Maximov, M. V. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Zhukov, A. E. [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Livshits, D. A. [Innolume GmbH (Germany); Payusov, A. S.; Nadtochiy, A. M. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation); Savelyev, A. V.; Kryzhanovskaya, N. V. [Russian Academy of Sciences, St. Petersburg Academic University-Nanotechnology Research and Education Center (Russian Federation); Gordeev, N. Yu. [Russian Academy of Sciences, Ioffe Physical-Technical Institute (Russian Federation)

    2013-12-15T23:59:59.000Z

    The spectral analysis of amplified spontaneous emission is used to determine the linewidth enhancement factor (?-factor) in lasers based on InAs/InGaAs quantum dots (QDs) in a wide spectral range near the ground-state optical transition energy. The effect of the pump current and number of QDs on the spectral dependences of the ?-factor is examined. The temperature dependence of the spectra of the ?-factor is experimentally determined for the first time for lasers with InAs/InGaAs QDs. An explanation is suggested for the observed anomalous decrease in the ?-factor with increasing temperature.

  17. Maximal tripartite entanglement between singlet-triplet qubits in quantum dots

    E-Print Network [OSTI]

    Tuukka Hiltunen; Ari Harju

    2013-10-24T23:59:59.000Z

    Singlet-triplet states in double quantum dots are promising realizations of qubits, and capacitive coupling can be used to create entanglement between these qubits. We propose an entangling three-qubit gate of singlet-triplet qubits in a triangular setup. Our simulations using a realistic microscopic model show that a maximally entangled Greenberger-Horne-Zeilinger state can be generated as the qubits are evolved under exchange. Furthermore, our analysis for the gate operation can be used to extract the actual experimental pulse sequence needed to realize this.

  18. Shaping the composition profiles in heteroepitaxial quantum dots: Interplay of thermodynamic and kinetic effects

    SciTech Connect (OSTI)

    Georgiou, C. [Research Unit for Nanostructured Materials Systems, Cyprus University of Technology, P.O. Box 50329, 3603 Limassol (Cyprus); Leontiou, T. [Research Unit for Nanostructured Materials Systems, Cyprus University of Technology, P.O. Box 50329, 3603 Limassol (Cyprus); General Department, Frederich University, 1036 Nicosia (Cyprus); Kelires, P. C., E-mail: pantelis.kelires@cut.ac.cy [Research Unit for Nanostructured Materials Systems, Cyprus University of Technology, P.O. Box 50329, 3603 Limassol (Cyprus); Department of Mechanical and Materials Science Engineering, Cyprus University of Technology, P.O. Box 50329, 3603 Limassol (Cyprus)

    2014-07-15T23:59:59.000Z

    Atomistic Monte Carlo simulations, coupling thermodynamic and kinetic effects, resolve a longstanding controversy regarding the origin of composition profiles in heteroepitaxial SiGe quantum dots. It is shown that profiles with cores rich in the unstrained (Si) component derive from near-equilibrium processes and intraisland diffusion. Profiles with cores rich in the strained (Ge) component are of nonequilibrium nature, i.e., they are strain driven but kinetically limited. They are shaped by the distribution of kinetic barriers of atomic diffusion in the islands. The diffusion pathways are clearly revealed for the first time. Geometrical kinetics play a minor role.

  19. Secondary treatment of films of colloidal quantum dots for optoelectronics and devices produced thereby

    DOE Patents [OSTI]

    Semonin, Octavi Escala; Luther, Joseph M; Beard, Matthew C; Chen, Hsiang-Yu

    2014-04-01T23:59:59.000Z

    A method of forming an optoelectronic device. The method includes providing a deposition surface and contacting the deposition surface with a ligand exchange chemical and contacting the deposition surface with a quantum dot (QD) colloid. This initial process is repeated over one or more cycles to form an initial QD film on the deposition surface. The method further includes subsequently contacting the QD film with a secondary treatment chemical and optionally contacting the surface with additional QDs to form an enhanced QD layer exhibiting multiple exciton generation (MEG) upon absorption of high energy photons by the QD active layer. Devices having an enhanced QD active layer as described above are also disclosed.

  20. Statistical distributions of level widths and conductance peaks in irregularly shaped quantum dots

    SciTech Connect (OSTI)

    Alhassid, Y.; Lewenkopf, C.H. [Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520 (United States)] [Center for Theoretical Physics, Sloane Physics Laboratory, Yale University, New Haven, Connecticut 06520 (United States); [Department of Physics, FM-15, University of Washington, Seattle, Washington 98195 (United States)

    1995-11-20T23:59:59.000Z

    Analytical expressions for width and conductance peak distributions for quantum dots with multichannel leads in the Coulomb blockade regime are presented for both limits of conserved and broken time-reversal symmetry. The results are valid for any number of nonequivalent and correlated channels, and the distributions are expressed in terms of the channel correlation matrix {ital M} in each lead. The matrix {ital M} is also given in closed form. A chaotic billiard is used as a model to test numerically the theoretical predictions. {copyright} {ital 1995} {ital The} {ital American} {ital Physical} {ital Society}.

  1. Mid infrared optical properties of Ge/Si quantum dots with different doping level

    SciTech Connect (OSTI)

    Sofronov, A. N.; Firsov, D. A.; Vorobjev, L. E.; Shalygin, V. A.; Panevin, V. Yu.; Vinnichenko, M. Ya. [St. Petersburg State Polytechnic University, Polytechnicheskaya str. 29, St. Petersburg (Russian Federation); Tonkikh, A. A. [Max Planck Institute of Microstructure Physics, Weinberg 2 D-06120, Halle (Saale) (Germany); Danilov, S. N. [University of Regensburg, Regensburg (Germany)

    2013-12-04T23:59:59.000Z

    Optical characterization of the Ge/Si quantum dots using equilibrium and photo-induced absorption spectroscopy in the mid-infrared spectral range was performed in this work. Equilibrium absorption spectra were measured in structures with various doping levels for different light polarizations. Photo-induced absorption spectra measured in undoped structure under interband optical excitation of non-equilibrium charge carriers demonstrate the same features as doped sample in equilibrium conditions. Hole energy spectrum was determined from the analysis of experimental data.

  2. Quantum Dot Tracers for Use in Engineered Geothermal | Department of Energy

    Office of Energy Efficiency and Renewable Energy (EERE) Indexed Site

    AFDC Printable Version Share this resource Send a link to EERE: Alternative Fuels Data Center Home Page to someone by E-mail Share EERE: Alternative Fuels Data Center Home Page on Facebook Tweet about EERE: Alternative Fuels Data Center Home Page on Twitter Bookmark EERE: Alternative Fuels Data Center Home Page on Google Bookmark EERE: Alternative Fuels DataDepartment of Energy Your Density Isn'tOrigin of ContaminationHubs+18, 2012 Qualified Energy ConservationDepartmentQuantum Dot Tracers

  3. Strain-induced vertical self-organization of semiconductor quantum dots: A computational study

    SciTech Connect (OSTI)

    Shtinkov, N., E-mail: nshtinkov@uottawa.ca [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa (Ontario) K1N 6N5 (Canada)

    2013-12-28T23:59:59.000Z

    Atomistic strain simulations based on the valence force field method are employed to study the vertical arrangements of semiconductor quantum dot (QD) multilayers. The effects of the QD shape, dimensions, and materials parameters are systematically investigated, varying independently the following parameters: spacer width H, QD lateral spacing D, base b, and height h, slope of the side facets, elastic properties of the dot and the substrate materials, and lattice mismatch between the dot and the substrate. The transition between vertically aligned and anti-aligned structures is found to be determined mainly by the ratios H/D and b/D, as well as by the strain anisotropy of the substrate and to a lesser extent of the QD. The dependence on the QD height h is significant only for steep side facets and large aspect ratios h/b, and the effects of the lattice mismatch strain and the bulk elastic moduli are found to be negligible. The comparison with experimental data shows an excellent agreement with the results from the simulations, demonstrating that the presented analysis results in precise theoretical predictions for the vertical self-organization regime in a wide range of QD materials systems.

  4. Room temperature infrared photoresponse of self assembled Ge/Si (001) quantum dots grown by molecular beam epitaxy

    SciTech Connect (OSTI)

    Singha, R. K.; Manna, S.; Das, S.; Dhar, A.; Ray, S. K. [Department of Physics and Meteorology, Indian Institute of Technology Kharagpur, Kharagpur 721302 (India)

    2010-06-07T23:59:59.000Z

    We report on the observation of intraband near infrared (approx3.1 mum) and mid infrared (approx6.2 mum) photocurrent response at room temperature using Ge/Si self-assembled quantum dots grown by molecular beam epitaxy. Due to the bimodal size distribution and SiGe intermixing, distinguishable photoluminescence transitions are observed at 10 K, below and above the optical band gap of bulk Ge. The observed redshift in photocurrent with increasing temperature has been explained by the excitonic electric field originated due to infrared excitation at low temperatures. A good correlation between the spectral photocurrent response and photoluminescence of the quantum dots has been established.

  5. Quantum information processing : science & technology.

    SciTech Connect (OSTI)

    Horton, Rebecca; Carroll, Malcolm S.; Tarman, Thomas David

    2010-09-01T23:59:59.000Z

    Qubits demonstrated using GaAs double quantum dots (DQD). The qubit basis states are the (1) singlet and (2) triplet stationary states. Long spin decoherence times in silicon spurs translation of GaAs qubit in to silicon. In the near term the goals are: (1) Develop surface gate enhancement mode double quantum dots (MOS & strained-Si/SiGe) to demonstrate few electrons and spin read-out and to examine impurity doped quantum-dots as an alternative architecture; (2) Use mobility, C-V, ESR, quantum dot performance & modeling to feedback and improve upon processing, this includes development of atomic precision fabrication at SNL; (3) Examine integrated electronics approaches to RF-SET; (4) Use combinations of numerical packages for multi-scale simulation of quantum dot systems (NEMO3D, EMT, TCAD, SPICE); and (5) Continue micro-architecture evaluation for different device and transport architectures.

  6. Elastic fields of quantum dots in subsurface layers A. E. Romanov

    E-Print Network [OSTI]

    Beltz, Glenn E.

    to vertical stacking of dots provided that the thickness of the intervening layer ``spacer layer'' is in the order or thinner than the lateral dimensions of the dot.4 It is now clear that dot ordering is driven

  7. Edge states in graphene quantum dots: Fractional quantum Hall effect analogies and differences at zero magnetic field

    E-Print Network [OSTI]

    Igor Romanovsky; Constantine Yannouleas; Uzi Landman

    2009-01-15T23:59:59.000Z

    We investigate the way that the degenerate manifold of midgap edge states in quasicircular graphene quantum dots with zig-zag boundaries supports, under free-magnetic-field conditions, strongly correlated many-body behavior analogous to the fractional quantum Hall effect (FQHE), familiar from the case of semiconductor heterostructures in high magnetic fields. Systematic exact-diagonalization (EXD) numerical studies are presented for the first time for 5 graphene REMs exhibit in all instances a single (0,N) polygonal-ring molecular (crystalline) structure, with all the electrons localized on the edge. Disruptions in the zig-zag boundary condition along the circular edge act effectively as impurities that pin the electron molecule, yielding single-particle densities with broken rotational symmetry that portray directly the azimuthal localization of the edge electrons.

  8. Multiple time scale blinking in InAs quantum dot single-photon sources

    E-Print Network [OSTI]

    Marcelo Davanco; C. Stephen Hellberg; Serkan Ates; Antonio Badolato; Kartik Srinivasan

    2014-04-21T23:59:59.000Z

    We use photon correlation measurements to study blinking in single, epitaxially-grown self-assembled InAs quantum dots situated in circular Bragg grating and microdisk cavities. The normalized second-order correlation function g(2)(\\tau) is studied across eleven orders of magnitude in time, and shows signatures of blinking over timescales ranging from tens of nanoseconds to tens of milliseconds. The g(2)(\\tau) data is fit to a multi-level system rate equation model that includes multiple non-radiating (dark) states, from which radiative quantum yields significantly less than 1 are obtained. This behavior is observed even in situations for which a direct histogramming analysis of the emission time-trace data produces inconclusive results.

  9. Light-assisted recharging of graphene quantum dots in fluorographene matrix

    SciTech Connect (OSTI)

    Antonova, I. V. [A.V. Rzhanov Institute of Semiconductor Physics, Russian Academy of Sciences, Siberian Branch, Acad. Lavrentiev Avenue 13, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Pirogov Street 2, Novosibirsk 630090 (Russian Federation); Nebogatikova, N. A.; Prinz, V. Ya. [A.V. Rzhanov Institute of Semiconductor Physics, Russian Academy of Sciences, Siberian Branch, Acad. Lavrentiev Avenue 13, Novosibirsk 630090 (Russian Federation); Popov, V. I.; Smagulova, S. A. [North - East Federal University, Yakutsk (Russian Federation)

    2014-10-07T23:59:59.000Z

    In the present study, the charge transient spectroscopy was used to analyze the transient relaxation of charges in graphene and bilayer-graphene quantum dot (QD) systems formed by chemical functionalization of graphene and few-layer graphene layers. A set of activation energies (one to three different values) for the emission of charges from QDs sized 50 to 70 nm, most likely proceeding via the thermal activation of charge carriers from QD quantum confinement levels, were deduced from measurements performed in the dark. Daylight illumination of samples during measurements was found to result in a strong decrease of the activation energies and in an involvement of an athermal process in the charge relaxation phenomenon. The time of the light-assisted emission of charge carriers from QDs proved to be two to four orders of magnitude shorter than the time of their emission from QDs under no-illumination conditions.

  10. Morphological evolution of seeded self-limiting quantum dots on patterned substrates

    SciTech Connect (OSTI)

    Dimastrodonato, Valeria; Pelucchi, Emanuele [Tyndall National Institute, University College Cork, Dyke Parade, Cork (Ireland); Vvedensky, Dimitri D. [The Blackett Laboratory, Imperial College London, London SW7 2AZ (United Kingdom)

    2013-12-04T23:59:59.000Z

    We present experimental data and a comprehensive theoretical model for the self-limiting growth during metalorganic vaporphase epitaxy of Al{sub x}Ga{sub 1?x}As within tetrahedral recesses etched in GaAs(111)B substrates. A self-limiting profile develops during growth, accompanied by Ga segregation, and leads to the formation of quantum dots and vertical quantum wires along the base and central axis of the recesses, respectively. A theoretical model based on reaction-diffusion equations for the precursor kinetics, adatom diffusion and incorporation, on each crystallographic facet composing the template, is formulated: our theory explains, and reproduces with good agreement, all the experimental trends of the self-limiting profile and alloy segregation dependence on material composition and growth temperature. These results represent a promising route toward a reproducible on-demand design of seeded lowdimensional nanostructures grown on any patterned surface.

  11. Polarization Response in InAs Quantum Dots: Theoretical Correlation between Composition and Electronic Properties

    E-Print Network [OSTI]

    Usman, Muhammad; Todaro, Maria Teresa; De Giorgi, Milena; O'Reilly, Eoin P; Klimeck, Gerhard; Passaseo, Adriana

    2012-01-01T23:59:59.000Z

    III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field ins...

  12. Electrostatically defined Quantum Dots in a Si/SiGe Heterostructure

    E-Print Network [OSTI]

    A. Wild; J. Sailer; J. Nützel; G. Abstreiter; S. Ludwig; D. Bougeard

    2010-07-14T23:59:59.000Z

    We present an electrostatically defined few-electron double quantum dot (QD) realized in a molecular beam epitaxy grown Si/SiGe heterostructure. Transport and charge spectroscopy with an additional QD as well as pulsed-gate measurements are demonstrated. We discuss technological challenges specific for silicon-based heterostructures and the effect of a comparably large effective electron mass on transport properties and tunability of the double QD. Charge noise, which might be intrinsically induced due to strain-engineering is proven not to affect the stable operation of our device as a spin qubit. Our results promise the suitability of electrostatically defined QDs in Si/SiGe heterostructures for quantum information processing.

  13. Electrostatically defined Quantum Dots in a Si/SiGe Heterostructure

    E-Print Network [OSTI]

    Wild, A; Nützel, J; Abstreiter, G; Ludwig, S; Bougeard, D

    2010-01-01T23:59:59.000Z

    We present an electrostatically defined few-electron double quantum dot (QD) realized in a molecular beam epitaxy grown Si/SiGe heterostructure. Transport and charge spectroscopy with an additional QD as well as pulsed-gate measurements are demonstrated. We discuss technological challenges specific for silicon-based heterostructures and the effect of a comparably large effective electron mass on transport properties and tunability of the double QD. Charge noise, which might be intrinsically induced due to strain-engineering is proven not to affect the stable operation of our device as a spin qubit. Our results promise the suitability of electrostatically defined QDs in Si/SiGe heterostructures for quantum information processing.

  14. Theoretical simulation of carrier capture and relaxation rates in quantum-dot semiconductor optical amplifiers

    SciTech Connect (OSTI)

    Wu, Yunhu [College of Physical Science and Technology, Central China Normal University, Wuhan 430079 (China); Department of Physics, Kashi Normal College, Kashi 844006 (China); Zhang, Guoping, E-mail: gpzhang@phy.ccnu.edu.cn [College of Physical Science and Technology, Central China Normal University, Wuhan 430079 (China); Guo, Ling; Qi, Guoqun [Department of Physics, Kashi Normal College, Kashi 844006 (China); Li, Xiaoming [Wuhan National Laboratory for Optoelectronics, School of Optical and Electronic Information, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2014-06-14T23:59:59.000Z

    Based on Auger scattering mechanism, carrier-carrier scattering dynamics between the two-dimensional carrier reservoir (also called wetting layer, i.e., WL) and the confined quantum dot ground and first excited state in quantum-dot semiconductor optical amplifiers (QD-SOAs) are investigated theoretically in this paper. The scattering rates for independent electron and hole densities are calculated. The results show an ultra-fast carrier capture (relaxation) rate up to 1 ps{sup ?1}, and there is a complex dependence of the Coulomb scattering rates on the WL electron and hole densities. In addition, due to the different effective mass and the level distribution, the scattering rates for electron and hole are very different. Finally, in order to provide a direction to control (increase or decrease) the input current in realistic QD-SOA systems, a simple method is proposed to determine the trends of the carrier recovery rates with the WL carrier densities in the vicinity of the steady-state.

  15. Revolutionary Method for Increasing the Efficiency of White Light Quantum Dot LEDs

    SciTech Connect (OSTI)

    Duty, Chad E [ORNL; Bennett, Charlee J C [ORNL; Sabau, Adrian S [ORNL; Jellison Jr, Gerald Earle [ORNL; Boudreaux, Philip R [ORNL; Walker, Steven C [ORNL; Ott, Ronald D [ORNL

    2011-01-01T23:59:59.000Z

    Covering a light-emitting diode (LED) with quantum dots (QDs) can produce a broad spectrum of white light. However, current techniques for applying QDs to LEDs suffer from a high density of defects and a non-uniform distribution of QDs, which respec-tively diminish the efficiency and quality of emitted light. Oak Ridge National Laboratory (ORNL) has the unique capability to thermally anneal QD structures at extremely high power densities for very short durations. This process, called pulse thermal proc-essing (PTP), reduces the number of point defects while main-taining the size and shape of the original QD nanostructure. Therefore, the efficiency of the QD wavelength conversion layer is improved without altering the emission spectrum defined by the size distribution of the quantum dot nanoparticles. The cur-rent research uses a thermal model to predict annealing tempera-tures during PTP and demonstrates up to a 300% increase in pho-toluminescence for QDs on passive substrates

  16. Effect of Ligands on Characteristics of (CdSe)13 Quantum Dot

    SciTech Connect (OSTI)

    Gao, Yang; Zhou, Bo; Kang, Seung-gu; Xin, Minsi; Yang, Ping; Dai, Xing; Wang, Zhigang; Zhou, Ruhong

    2014-01-01T23:59:59.000Z

    The widespread applications of quantum dots (QDs) have spurred an increasing interest in the study of their coating ligands, which can not only protect the electronic structures of the central QDs, but also control their permeability through biological membranes with both size and shape. In this work, we have used density functional theory (DFT) to investigate the electronic structures of (CdSe)13 passivated by OPMe2(CH2)nMe ligands with different lengths and various numbers of branches (Me=methyl group, n = 0, 1-3). Our results show that the absorption peak in the ultraviolet-visible (UV-vis) spectra displays a clear blue-shift, on the scale of ~100 nm, upon the binding of ligands. Once the total number of ligands bound with (CdSe)13 reached a saturated number (9 or 10), no more blue-shift occurred in the absorption peak in the UV-vis spectra. On the other hand, the aliphatic chain length of ligands has a negligible effect on the optical properties of the QD core. Analyses of the bonding characteristics confirm that optical transitions are dominantly governed by the central QD core rather than the organic passivation. Interestingly, the density of states (DOS) share similar characteristics as vibrational spectra, even though there is no coordination vibration mode between the ligands and the central QD. These findings might provide insights on the material design for the passivation of quantum dots for biomedical applications.

  17. Theory of Linear Optical Absorption in Diamond Shaped Graphene Quantum Dots

    E-Print Network [OSTI]

    Basak, Tista; Shukla, Alok

    2015-01-01T23:59:59.000Z

    In this paper, optical and electronic properties of diamond shaped graphene quantum dots (DQDs) have been studied by employing large-scale electron-correlated calculations. The computations have been performed using the $\\pi$-electron Pariser-Parr-Pople model Hamiltonian, which incorporates long-range Coulomb interactions. The influence of electron-correlation effects on the ground and excited states has been included by means of the configuration-interaction approach, used at various levels. Our calculations have revealed that the absorption spectra are red-shifted with the increasing sizes of quantum dots. It has been observed that the first peak of the linear optical absorption, which represents the optical gap, is not the most intense peak. This result is in excellent agreement with the experimental data, but in stark contrast to the predictions of the tight-binding model, according to which the first peak is the most intense peak, pointing to the importance of electron-correlation effects. Furthermore, a...

  18. Quantum Dot Light Enhancement Substrate for OLED Solid-State Lighting

    SciTech Connect (OSTI)

    James Perkins; Matthew Stevenson; Gagan Mahan; Seth Coe-Sullivan; Peter Kazlas

    2011-01-21T23:59:59.000Z

    With DOE Award No. DE-EE00000628, QD Vision developed and demonstrated a cost-competitive solution for increasing the light extraction efficiency of OLEDs with efficient and stable color rendering index (CRI) for solid state lighting (SSL). Solution processable quantum dot (QD) films were integrated into OLED ITO-glass substrates to generate tunable white emission from blue emitting OLED) devices as well as outcouple light from the ITO film. This QD light-enhancement substrate (QD-LED) technology demonstrated a 60% increase in OLED forward light out-coupling, a value which increases to 76% when considering total increase in multi-directional light output. The objective for the first year was an 80% increase in light output. This project seeks to develop and demonstrate a cost-competitive solution for realizing increased extraction efficiency organic light emitting devices (OLEDs) with efficient and stable color rendering index (CRI) for SSL. Solution processible quantum dot (QD) films will be utilized to generate tunable white emission from blue emitting phosphorescent OLED (Ph-OLED) devices.

  19. Polarized emission lines from A-and B-type excitonic complexes in single InGaN/GaN quantum dots

    E-Print Network [OSTI]

    Nabben, Reinhard

    Polarized emission lines from A- and B-type excitonic complexes in single InGaN/GaN quantum dots M Cathodoluminescence measurements on single InGaN/GaN quantum dots QDs are reported. Complex spectra with up to five spectral region have been realized based on InGaN structures.1 Single-photon emission from GaN/AlN quantum

  20. THE JOURNAL OF CHEMICAL PHYSICS 136, 194106 (2012) Trapping photon-dressed Dirac electrons in a quantum dot studied

    E-Print Network [OSTI]

    Mukamel, Shaul

    2012-01-01T23:59:59.000Z

    and bilayer graphene by spatially different potential profiles. Short lived exci- tonic states which are too unique band structure, the charge carriers in graphene are massless Dirac fermions which can cross high to be localized within graphene based quantum dots (QDs). Within a finite spatial region defined by sharp

  1. Long-time electron spin storage via dynamical suppression of hyperfine-induced decoherence in a quantum dot

    E-Print Network [OSTI]

    by the nuclear spin environment in a quantum dot can be substantially increased by subjecting the electron and characterized. The impact of system and control nonidealities is also assessed, including the effect.125336 PACS number s : 03.67.Pp, 03.65.Yz, 75.10.Jm, 02.60.Cb I. INTRODUCTION Electron and nuclear spin

  2. The Architecture of Colloidal Quantum Dot Solar Cells: Materials to Illan J. Kramer and Edward H. Sargent*

    E-Print Network [OSTI]

    The Architecture of Colloidal Quantum Dot Solar Cells: Materials to Devices Illan J. Kramer of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4, Canada CONTENTS 1. Introduction 863 2. Measuring and Modeling CQD Solar Cells 863 2.1. Solar Cell Characterization Considerations 864 2.2. Drift

  3. Intrazeolite metal carbonyl phototopotaxy: From Tungsten(VI) oxide quantum dots to a zero-dimensional semiconductor quantum supralattice

    SciTech Connect (OSTI)

    Ozin, G.A.; Oezkar, S. (Univ. of Toronto, Ontario (Canada))

    1990-09-20T23:59:59.000Z

    Attention is focused on the use of simple binary metal carbonyls for the nucleation, growth, and stabilization of intrazeolite semiconductor quantum nanostructures. The rationale for selecting this particular group of precursor molecules relates to their volatility, molecular dimensions, ease of purification, availability, and facile and quantitative conversion to the respective metal oxide materials with minimal contamination by carbon. In this study the intrazeolite photooxidation chemistry of {alpha}-cage encapsulated hexacarbonyltungsten(0) in Na{sub 56}Y and H{sub 56}Y, n(W(CO){sub 6})-Na{sub 56}Y(H{sub 56}Y), with O{sub 2} provides a novel synthetic pathway to {alpha}-cage-located tungsten(VI) oxide n(WO{sub 3})-Na{sub 56}Y(H{sub 56}Y) intrazeolite quantum dots and a zero-dimensional semiconductor quantum supralattice (where n = 0-32), which might find applications as new solid-state materials for use in quantum electronic and nonlinear optic devices.

  4. Adiabatic many-body state preparation and information transfer in quantum dot arrays

    E-Print Network [OSTI]

    Umer Farooq; Abolfazl Bayat; Stefano Mancini; Sougato Bose

    2015-04-27T23:59:59.000Z

    Quantum simulation of many-body systems are one of the most interesting tasks of quantum technology. Among them is the preparation of a many-body system in its ground state when the vanishing energy gap makes the cooling mechanisms ineffective. Adiabatic theorem, as an alternative to cooling, can be exploited for driving the many-body system to its ground state. In this paper, we study two most common disorders in quantum dot arrays, namely exchange coupling fluctuations and hyperfine interaction, in adiabatically preparation of ground state in such systems. We show that the adiabatic ground state preparation is highly robust against those disorder effects making it good analog simulator. Moreover, we also study the adiabatic classical information transfer, using singlet-triplet states, across a spin chain. In contrast to ground state preparation the transfer mechanism is highly affected by disorder and in particular, the hyperfine interaction is very destructive for the performance. This suggests that for communication tasks across such arrays adiabatic evolution is not as effective and quantum quenches could be preferable.

  5. Adiabatic many-body state preparation and information transfer in quantum dot arrays

    E-Print Network [OSTI]

    Umer Farooq; Abolfazl Bayat; Stefano Mancini; Sougato Bose

    2014-11-05T23:59:59.000Z

    Quantum simulation of many-body systems are one of the most interesting tasks of quantum technology. Among them is the preparation of a many-body system in its ground state when the vanishing energy gap makes the cooling mechanisms ineffective. Adiabatic theorem, as an alternative to cooling, can be exploited for driving the many-body system to its ground state. In this paper, we study two most common disorders in quantum dot arrays, namely exchange coupling fluctuations and hyperfine interaction, in adiabatically preparation of ground state in such systems. We show that the adiabatic ground state preparation is highly robust against those disorder effects making it good analog simulator. Moreover, we also study the adiabatic classical information transfer, using singlet-triplet states, across a spin chain. In contrast to ground state preparation the transfer mechanism is highly affected by disorder and in particular, the hyperfine interaction is very destructive for the performance. This suggests that for communication tasks across such arrays adiabatic evolution is not as effective and quantum quenches could be preferable.

  6. Study of the growth mechanisms of GaN/(Al, Ga)N quantum dots: Correlation between structural and optical properties

    SciTech Connect (OSTI)

    Sergent, S. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); Universite de Nice Sophia Antipolis, Parc Valrose, F-06102 Nice Cedex 2 (France); Damilano, B.; Huault, T.; Brault, J.; Tottereau, O.; Vennegues, P.; Leroux, M.; Semond, F.; Massies, J. [CRHEA-CNRS, Rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); Korytov, M.

    2011-03-01T23:59:59.000Z

    The ammonia-based molecular beam epitaxy of GaN/(Al, Ga)N quantum dots is investigated using reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy and photoluminescence. The main steps of the formation kinetics are identified and the influence of diffusion and evaporation processes on both the quantum dot and the wetting layer morphology is addressed. The correlation between the optical and structural properties of such structures finally allows for the analysis of matter exchanges between the quantum dots and the wetting layer during capping.

  7. IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 47, NO. 1, JANUARY 2011 31 All-Optical Switch Using Quantum-Dot Saturable

    E-Print Network [OSTI]

    Waks, Edo

    energy consumption of 3.91 fJ per bit are possible. Index Terms--Optical switches, quantum-dot. I to route data, which imposes limitations on transmission speed and power consumption. Methods for all of optical switching devices has been a subject of some debate. All-optical switching energies

  8. Two-photon interference from a quantum dot--microcavity: Persistent pure-dephasing and suppression of time-jitter

    E-Print Network [OSTI]

    Sebastian Unsleber; Dara P. S. McCutcheon; Michael Dambach; Matthias Lermer; Niels Gregersen; Sven Höfling; Jesper Mørk; Christian Schneider; Martin Kamp

    2015-03-03T23:59:59.000Z

    We demonstrate the emission of highly indistinguishable photons from a quasi-resonantly pumped coupled quantum dot--microcavity system operating in the regime of cavity quantum electrodynamics. Changing the sample temperature allows us to vary the quantum dot--cavity detuning, and on spectral resonance we observe a three-fold improvement in the Hong--Ou--Mandel interference visibility, reaching values in excess of 80\\%. Our measurements off-resonance allow us to investigate varying Purcell enhancements, and to probe the dephasing environment at different temperatures and energy scales. By comparison with our microscopic model, we are able to identify pure-dephasing and not time-jitter as the dominating source of imperfections in our system.

  9. Lagrange mesh and exact diagonalization for numerical study of semiconductor quantum dot systems with application in singlet-triplet qubits

    E-Print Network [OSTI]

    Tuukka Hiltunen; Juha Ritala; Oona Kupiainen; Topi Siro; Ari Harju

    2013-01-28T23:59:59.000Z

    We present a highly flexible computational scheme for studying correlated electrons confined by an arbitrary external potential in two-dimensional semiconductor quantum dots. The method starts by a Lagrange mesh calculation for the single-particle states, followed by the calculation of the Coulomb interaction matrix elements between these, and combining both in the exact diagonalization of the many-body Hamiltonian. We apply the method in simulation of double quantum dot singlet-triplet qubits. We simulate the full quantum control and dynamics of one singlet-triplet qubit. We also use our method to provide an exact diagonalization based first-principles model for studying two singlet-triplet qubits and their capacitative coupling via the long-distance Coulomb interaction.

  10. Wavelength-tunable colloidal quantum dot laser on ultra-thin flexible glass

    SciTech Connect (OSTI)

    Foucher, C.; Guilhabert, B.; Laurand, N.; Dawson, M. D. [Institute of Photonics, SUPA, University of Strathclyde, Glasgow (United Kingdom)

    2014-04-07T23:59:59.000Z

    A mechanically flexible and wavelength-tunable laser with an ultra-thin glass membrane as substrate is demonstrated. The optically pumped hybrid device has a distributed feedback cavity that combines a colloidal quantum dot gain film with a grating-patterned polymeric underlayer, all on a 30-?m thick glass sheet. The total thickness of the structure is only 75??m. The hybrid laser has an average threshold fluence of 450?±?80??J/cm{sup 2} (for 5-ns excitation pulses) at an emitting wavelength of 607?nm. Mechanically bending the thin-glass substrate enables continuous tuning of the laser emission wavelength over an 18-nm range, from 600?nm to 618?nm. The correlation between the wavelength tunability and the mechanical properties of the thin laser structure is verified theoretically and experimentally.

  11. Optical and Electrical Measurement of Energy Transfer between Nanocrystalline Quantum Dots and Photosystem I

    SciTech Connect (OSTI)

    Jung, H.; Gulis, G.; Gupta, S.; Redding, K.; Gosztola, D. J.; Wiederrecht, Gary P; Stroscio, M. A.; Dutta, M.

    2010-01-01T23:59:59.000Z

    In the natural photosynthesis process, light harvesting complexes (LHCs) absorb light and pass excitation energy to photosystem I (PSI) and photosystem II (PSII). In this study, we have used nanocrystalline quantum dots (NQDs) as an artificial LHC by integrating them with PSI to extend their spectral range. We have performed photoluminescence (PL) and ultrafast time-resolved absorption measurements to investigate this process. Our PL experiments showed that emission from the NQDs is quenched, and the fluorescence from PSI is enhanced. Transient absorption and bleaching results can be explained by fluorescence resonance energy transfer (FRET) from the NQDs to the PSI. This nonradiative energy transfer occurs in ?6 ps. Current?voltage (I?V) measurements on the composite NQD-PSI samples demonstrate a clear photoresponse.

  12. Ge{sub 1-x}Mn{sub x} heteroepitaxial quantum dots: Growth, morphology, and magnetism

    SciTech Connect (OSTI)

    Kassim, J.; Nolph, C.; Reinke, P.; Floro, J. [Department of Materials Science and Engineering, University of Virginia, Charlottesville, Virginia 22904 (United States); Jamet, M. [Institut Nanosciences et Cryogenie/SP2M, CEA-UJF, F-38054 Grenoble (France)

    2013-02-21T23:59:59.000Z

    Heteroepitaxial Ge{sub 1-x}Mn{sub x} quantum dots (QDs) were grown on Si (001) by molecular beam epitaxial co-deposition, with x = 0 to 0.10, in order to explore the interaction between Mn content, surface morphological evolution, and magnetism. Morphological evolution typical of the Ge/Si (001) system was observed, where the effect of Mn on surface morphology is surprisingly minimal at low Mn content, with no obvious surface morphological indicators of second phase formation. As the Mn content increases, secondary phase formation becomes evident, appearing to heterogeneously nucleate on or within Ge QDs. Still higher Mn concentrations lead to extensive second phase formation interspersed with an array of Ge QDs. Although ferromagnetism up to 220 K is observed, likely arising from intermetallic precipitates, there is no clear evidence for room-temperature ferromagnetism associated with a dilute magnetic solution phase.

  13. A scheme comparison of Autler-Townes based slow light in inhomogeneously broadened quantum dot media

    E-Print Network [OSTI]

    Per Lunnemann; Jesper Mørk

    2010-08-23T23:59:59.000Z

    We propose a method to achieve significant optical signal delays exploiting the effect of Autler-Townes splitting in an inhomogeneously broadened quantum dot medium. The absorption and slow-down effects are compared for three schemes i.e. $\\Xi$, V and $\\Lambda$, corresponding to different excitation configurations. Qualitative differences of the V-scheme compared to the $\\Xi$- and $\\Lambda$-scheme are found, which show that features of Autler-Townes splitting are only revealed in the V-scheme. The underlying physical mechanisms causing this discrepancy are analyzed and discussed. Finally we compare field propagation calculations of the schemes showing significantly larger achievable signal delays for the V-scheme despite finite absorption of the coupling field. This opens the possibility for using waveguide structures for both coupling and probe fields, thus significantly increasing the achievable signal delays.

  14. Advanced method for increasing the efficiency of white light quantum dot LEDs

    SciTech Connect (OSTI)

    Duty, Chad E [ORNL; Bennett, Charlee J C [ORNL; Sabau, Adrian S [ORNL; Jellison Jr, Gerald Earle [ORNL; Boudreaux, Philip R [ORNL; Walker, Steven C [ORNL; Ott, Ronald D [ORNL

    2011-01-01T23:59:59.000Z

    Covering a light-emitting diode (LED) with quantum dots (QDs) can produce a broad spectrum of white light. However, current techniques for applying QDs to LEDs suffer from a high density of defects and a non-uniform distribution of QDs, which, respectively, diminish the efficiency and quality of emitted light. Oak Ridge National Laboratory (ORNL) has the unique capability to thermally anneal QD structures at extremely high power densities for very short durations. This process, called pulse thermal processing (PTP), reduces the number of point defects while maintaining the size and shape of the original QD nanostructure. Therefore, the efficiency of the QD wavelength conversion layer is improved without altering the emission spectrum defined by the size distribution of theQD nanoparticles. The current research uses a thermal model to predict annealing temperatures during PTP and demonstrates up to a 300% increase in photoluminescence for QDs on passive substrates.

  15. Controlling the Spontaneous Emission Rate of Single Quantum Dots in a 2D Photonic Crystal

    E-Print Network [OSTI]

    Dirk Englund; David Fattal; Edo Waks; Glenn Solomon; Bingyang Zhang; Toshihiro Nakaoka; Yasuhiko Arakawa; Yoshihisa Yamamoto; Jelena Vuckovic

    2005-04-20T23:59:59.000Z

    We observe large spontaneous emission rate modification of individual InAs Quantum Dots (QDs) in 2D a photonic crystal with a modified, high-Q single defect cavity. Compared to QDs in bulk semiconductor, QDs that are resonant with the cavity show an emission rate increase by up to a factor of 8. In contrast, off-resonant QDs indicate up to five-fold rate quenching as the local density of optical states (LDOS) is diminished in the photonic crystal. In both cases we demonstrate photon antibunching, showing that the structure represents an on-demand single photon source with pulse duration from 210 ps to 8 ns. We explain the suppression of QD emission rate using Finite Difference Time Domain (FDTD) simulations and find good agreement with experiment.

  16. Strongly modified four-wave mixing in a coupled semiconductor quantum dot-metal nanoparticle system

    SciTech Connect (OSTI)

    Paspalakis, Emmanuel, E-mail: paspalak@upatras.gr [Materials Science Department, School of Natural Sciences, University of Patras, 265 04 Patras (Greece); Evangelou, Sofia [Materials Science Department, School of Natural Sciences, University of Patras, 265 04 Patras (Greece); Department of Materials Science and Engineering, University of Ioannina, Ioannina 45110 (Greece); Kosionis, Spyridon G.; Terzis, Andreas F. [Department of Physics, School of Natural Sciences, University of Patras, 265 04 Patras (Greece)

    2014-02-28T23:59:59.000Z

    We study the four-wave mixing effect in a coupled semiconductor quantum dot-spherical metal nanoparticle structure. Depending on the values of the pump field intensity and frequency, we find that there is a critical distance that changes the form of the spectrum. Above this distance, the four-wave mixing spectrum shows an ordinary three-peaked form and the effect of controlling its magnitude by changing the interparticle distance can be obtained. Below this critical distance, the four-wave mixing spectrum becomes single-peaked; and as the interparticle distance decreases, the spectrum is strongly suppressed. The behavior of the system is explained using the effective Rabi frequency that creates plasmonic metaresonances in the hybrid structure. In addition, the behavior of the effective Rabi frequency is explained via an analytical solution of the density matrix equations.

  17. Suspending Effect on Low-Frequency Charge Noise in Graphene Quantum Dot

    E-Print Network [OSTI]

    Xiang-Xiang Song; Hai-Ou Li; Jie You; Tian-Yi Han; Gang Cao; Tao Tu; Ming Xiao; Guang-Can Guo; Hong-Wen Jiang; Guo-Ping Guo

    2014-06-16T23:59:59.000Z

    Charge noise is critical in the performance of gate-controlled quantum dots (QDs). Here we show the 1/f noise for a microscopic graphene QD is substantially larger than that for a macroscopic graphene field-effect transistor (FET), increasing linearly with temperature. To understand its origin, we suspended the graphene QD above the substrate. In contrast to large area graphene FETs, we find that a suspended graphene QD has an almost-identical noise level as an unsuspended one. Tracking noise levels around the Coulomb blockade peak as a function of gate voltage yields potential fluctuations of order 1 "{\\mu}eV", almost one order larger than in GaAs/GaAlAs QDs. Edge states rather than substrate-induced disorders, appear to dominate the 1/f noise, thus affecting the coherency of graphene nano-devices.

  18. Charge tuning in [111] grown GaAs droplet quantum dots

    SciTech Connect (OSTI)

    Bouet, L.; Vidal, M.; Marie, X.; Amand, T.; Wang, G.; Urbaszek, B. [INSA-CNRS-UPS, LPCNO, Université de Toulouse, 135 Ave. Rangueil, 31077 Toulouse (France); Mano, T.; Ha, N.; Kuroda, T.; Sakoda, K. [National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044 (Japan); Durnev, M. V.; Glazov, M. M.; Ivchenko, E. L. [Ioffe Physical-Technical Institute RAS, 194021 St.-Petersburg (Russian Federation)

    2014-08-25T23:59:59.000Z

    We demonstrate charge tuning in strain free GaAs/AlGaAs quantum dots (QDs) grown by droplet epitaxy on a GaAs(111)A substrate. Application of a bias voltage allows the controlled charging of the QDs from ?3|e| to +2|e|. The resulting changes in QD emission energy and exciton fine-structure are recorded in micro-photoluminescence experiments at T?=?4?K. We uncover the existence of excited valence and conduction states, in addition to the s-shell-like ground state. We record a second series of emission lines about 25?meV above the charged exciton emission coming from excited charged excitons. For these excited interband transitions, a negative diamagnetic shift of large amplitude is uncovered in longitudinal magnetic fields.

  19. Tuning the external optical feedback-sensitivity of a passively mode-locked quantum dot laser

    SciTech Connect (OSTI)

    Raghunathan, R., E-mail: raghunat@vt.edu; Kovanis, V.; Lester, L. F. [Bradley Department of Electrical and Computer Engineering, Virginia Polytechnic Institute and State University, 302 Whittemore Hall, Blacksburg, Virginia 24061 (United States); Grillot, F. [Télécom ParisTech, Ecole Nationale Supérieure des Télécommunications, CNRS LTCI, 46 rue Barrault, 75634 Paris Cedex 13 (France); Mee, J. K.; Murrell, D. [Center for High Technology Materials, University of New Mexico, 1313 Goddard SE, Albuquerque, New Mexico 87106 (United States)

    2014-07-28T23:59:59.000Z

    The external optical feedback-sensitivity of a two-section, passively mode-locked quantum dot laser operating at elevated temperature is experimentally investigated as a function of absorber bias voltage. Results show that the reverse-bias voltage on the absorber has a direct impact on the damping rate of the free-running relaxation oscillations of the optical signal output, thereby enabling interactive external control over the feedback-response of the device, even under the nearly resonant cavity configuration. The combination of high temperature operation and tunable feedback-sensitivity is highly promising from a technological standpoint, in particular, for applications requiring monolithic integration of multi-component architectures on a single chip in order to accomplish, for instance, the dual-objectives of stable pulse quality and isolation from parasitic reflections.

  20. Charge Relaxation in a Single Electron Si/SiGe Double Quantum Dot

    E-Print Network [OSTI]

    K. Wang; C. Payette; Y. Dovzhenko; P. W. Deelman; J. R. Petta

    2013-04-15T23:59:59.000Z

    We measure the interdot charge relaxation time T_1 of a single electron trapped in an accumulation mode Si/SiGe double quantum dot. The energy level structure of the charge qubit is determined using photon assisted tunneling, which reveals the presence of a low lying excited state. We systematically measure T_1 as a function of detuning and interdot tunnel coupling and show that it is tunable over four orders of magnitude, with a maximum of 45 microseconds for our device configuration. Measured relaxation times are consistent with a phonon mediated energy relaxation process and indicate that low lying excited states may have important implications in the development of silicon spin qubits.

  1. Composite materials with metal oxide attached to lead chalcogenide nanocrystal quantum dots with linkers

    DOE Patents [OSTI]

    Fuke, Nobuhiro; Koposov, Alexey Y; Sykora, Milan; Hoch, Laura

    2014-12-16T23:59:59.000Z

    Composite materials useful for devices such as photoelectrochemical solar cells include a substrate, a metal oxide film on the substrate, nanocrystalline quantum dots (NQDs) of lead sulfide, lead selenide, and lead telluride, and linkers that attach the NQDs to the metal oxide film. Suitable linkers preserve the 1s absorption peak of the NQDs. A suitable linker has a general structure A-B-C where A is a chemical group adapted for binding to a MO.sub.x and C is a chemical group adapted for binding to a NQD and B is a divalent, rigid, or semi-rigid organic spacer moiety. Other linkers that preserve the 1s absorption peak may also be used.

  2. Carrier capture dynamics of single InGaAs/GaAs quantum-dot layers

    SciTech Connect (OSTI)

    Chauhan, K. N.; Riffe, D. M.; Everett, E. A.; Kim, D. J.; Yang, H. [Physics Department, Utah State University, Logan, Utah 84322-4415 (United States)] [Physics Department, Utah State University, Logan, Utah 84322-4415 (United States); Shen, F. K. [Center for Surface Analysis and Applications, Utah State University, Logan, Utah 84322-4415 (United States)] [Center for Surface Analysis and Applications, Utah State University, Logan, Utah 84322-4415 (United States)

    2013-05-28T23:59:59.000Z

    Using 800 nm, 25-fs pulses from a mode locked Ti:Al{sub 2}O{sub 3} laser, we have measured the ultrafast optical reflectivity of MBE-grown, single-layer In{sub 0.4}Ga{sub 0.6}As/GaAs quantum-dot (QD) samples. The QDs are formed via two-stage Stranski-Krastanov growth: following initial InGaAs deposition at a relatively low temperature, self assembly of the QDs occurs during a subsequent higher temperature anneal. The capture times for free carriers excited in the surrounding GaAs (barrier layer) are as short as 140 fs, indicating capture efficiencies for the InGaAs quantum layer approaching 1. The capture rates are positively correlated with initial InGaAs thickness and annealing temperature. With increasing excited carrier density, the capture rate decreases; this slowing of the dynamics is attributed to Pauli state blocking within the InGaAs quantum layer.

  3. Indirect and direct optical transitions in In{sub 0.5}Ga{sub 0.5}As/GaP quantum dots

    SciTech Connect (OSTI)

    Stracke, G., E-mail: gernot.stracke@tu-berlin.de; Sala, E. M.; Schliwa, A.; Strittmatter, A.; Bimberg, D. [Institut für Festkörperphysik, Technische Universität Berlin, Hardenbergstrasse 36, 10623 Berlin (Germany); Selve, S. [Zentraleinrichtung Elektronenmikroskopie, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany); Niermann, T. [Institut für Optik und Atomare Physik, Technische Universität Berlin, Straße des 17. Juni 135, 10623 Berlin (Germany)

    2014-03-24T23:59:59.000Z

    We present a study of self-assembled In{sub 0.5}Ga{sub 0.5}As quantum dots on GaP(001) surfaces linking growth parameters with structural, optical, and electronic properties. Quantum dot densities from 5.0 × 10{sup 7} cm{sup ?2} to 1.5 × 10{sup 11} cm{sup ?2} are achieved. A ripening process during a growth interruption after In{sub 0.5}Ga{sub 0.5}As deposition is used to vary the quantum dot size. The main focus of this work lies on the nature of optical transitions which can be switched from low-efficient indirect to high-efficient direct ones through improved strain relief of the quantum dots by different cap layers.

  4. An electrically driven quantum dot-in-nanowire visible single photon source operating up to 150 K

    SciTech Connect (OSTI)

    Deshpande, Saniya; Bhattacharya, Pallab [Center for Photonics and Multiscale Nanomaterials, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)] [Center for Photonics and Multiscale Nanomaterials, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)

    2013-12-09T23:59:59.000Z

    We demonstrate electrically pumped single photon emission up to 150 K from a single InGaN quantum dot embedded in a GaN nanowire junction diode. The InGaN dot-in-nanowire p-n junctions were grown on silicon by molecular beam epitaxy. The exciton electroluminescence from individual dot-in-nanowires is in the green spectral range (? ? 520 nm) and is detectable up to 150 K. Second order autocorrelation measurements performed at the exciton energy at an ambient temperature of 125 K show a background corrected g{sup (2)}(0) equal to 0.35, indicating dominant single photon emission. The steady state nanowire temperature under these conditions is estimated to be 150 K due to Joule heating induced by the large nanowire series resistance. Time resolved photoluminescence measurements yield an exciton radiative lifetime of 1.1 ns.

  5. Mesoporous TiO2 beads for high efficiency CdS/ CdSe quantum dot co-sensitized solar cells

    E-Print Network [OSTI]

    Cao, Guozhong

    ) as a derivative of dye-sensitized solar cells (DSCs) have attracted considerable attention and been regardedMesoporous TiO2 beads for high efficiency CdS/ CdSe quantum dot co-sensitized solar cells Ru Zhou for a CdS/CdSe quantum dot (QD) co-sensitized solar cell, which was constructed with the mesoporous TiO2

  6. Photo-modulated thin film transistor based on dynamic charge transfer within quantum-dots-InGaZnO interface

    SciTech Connect (OSTI)

    Liu, Xiang [Electronic Science and Engineering School, Southeast University, Nanjing (China); National Center for Nanoscience and Technology, Beijing (China); Yang, Xiaoxia; Liu, Mingju [National Center for Nanoscience and Technology, Beijing (China); Tao, Zhi; Wei, Lei, E-mail: lw@seu.edu.cn; Li, Chi, E-mail: lichi@seu.edu.cn; Zhang, Xiaobing; Wang, Baoping [Electronic Science and Engineering School, Southeast University, Nanjing (China); Dai, Qing, E-mail: daiq@nanoctr.cn [National Center for Nanoscience and Technology, Beijing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom); Nathan, Arokia [Electronic Science and Engineering School, Southeast University, Nanjing (China); London Center for Nanotechnology, University College London, London WC1H 0AH (United Kingdom)

    2014-03-17T23:59:59.000Z

    The temporal development of next-generation photo-induced transistor across semiconductor quantum dots and Zn-related oxide thin film is reported in this paper. Through the dynamic charge transfer in the interface between these two key components, the responsibility of photocurrent can be amplified for scales of times (?10{sup 4}?A/W 450?nm) by the electron injection from excited quantum dots to InGaZnO thin film. And this photo-transistor has a broader waveband (from ultraviolet to visible light) optical sensitivity compared with other Zn-related oxide photoelectric device. Moreover, persistent photoconductivity effect can be diminished in visible waveband which lead to a significant improvement in the device's relaxation time from visible illuminated to dark state due to the ultrafast quenching of quantum dots. With other inherent properties such as integrated circuit compatible, low off-state current and high external quantum efficiency resolution, it has a great potential in the photoelectric device application, such as photodetector, phototransistor, and sensor array.

  7. Photo-physical properties enhancement of bare and core-shell quantum dots

    SciTech Connect (OSTI)

    Mumin, Md Abdul, E-mail: pcharpentier@eng.uwo.ca; Akhter, Kazi Farida, E-mail: pcharpentier@eng.uwo.ca; Charpentier, Paul A., E-mail: pcharpentier@eng.uwo.ca [Chemical and Biochemical Engineering, Western University, London Ontario (Canada)

    2014-03-31T23:59:59.000Z

    Semiconductor nanocrystals (NCs) (also known as quantum dots, QDs) have attracted immense attention for their size-tunable optical properties that makes them impressive candidates for solar cells, light emitting devices, lasers, as well as biomedical imaging. However monodispersity, high and consistent photoluminescence, photostability, and biocompatibility are still major challenges. This work focuses on optimizing the photophysical properties and biocompatibility of QDs by forming core-shell nanostructures and their encapsulation by a carrier. Highly luminescent CdS and CdS-ZnS core-shell QDs with 5 nm sizes were synthesized using a facile approach based on pyrolysis of the single molecule precursors. After capping the CdS QDs with a thin layer of ZnS to reduce toxicity, the photoluminescence and photostability of the core-shell QDs was significantly enhanced. To make both the bare and core/shell structure QDs more resistant against photochemical reactions, a mesoporous silica layer was grown on the QDs through a reverse microemulsion technique based on hydrophobic interaction. This encapsulation enhanced the quantum yield and photostability compared to the bare QDs by providing much stronger resistance to oxidation and Oswald ripening of QDs. Encapsulation also improved biocompatibility of QDs that was evaluated with human umbilical vein endothelial cell lines (HUVEC)

  8. Polarization Response in InAs Quantum Dots: Theoretical Correlation between Composition and Electronic Properties

    E-Print Network [OSTI]

    Muhammad Usman; Vittorianna Tasco; Maria Teresa Todaro; Milena De Giorgi; Eoin P. O'Reilly; Gerhard Klimeck; Adriana Passaseo

    2012-03-17T23:59:59.000Z

    III-V growth and surface conditions strongly influence the physical structure and resulting optical properties of self-assembled quantum dots (QDs). Beyond the design of a desired active optical wavelength, the polarization response of QDs is of particular interest for optical communications and quantum information science. Previous theoretical studies based on a pure InAs QD model failed to reproduce experimentally observed polarization properties. In this work, multi-million atom simulations are performed to understand the correlation between chemical composition and polarization properties of QDs. A systematic analysis of QD structural parameters leads us to propose a two layer composition model, mimicking In segregation and In-Ga intermixing effects. This model, consistent with mostly accepted compositional findings, allows to accurately fit the experimental PL spectra. The detailed study of QD morphology parameters presented here serves as a tool for using growth dynamics to engineer the strain field inside and around the QD structures, allowing tuning of the polarization response.

  9. Optical pulse dynamics for quantum-dot logic operations in a photonic-crystal waveguide

    SciTech Connect (OSTI)

    Ma, Xun; John, Sajeev [Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7 Canada (Canada)

    2011-11-15T23:59:59.000Z

    We numerically demonstrate all-optical logic operations with quantum dots (QDs) embedded in a bimodal photonic-crystal waveguide using Maxwell-Bloch equations in a slowly varying envelope approximation (SVEA). The two-level QD excitation level is controlled by one or more femtojoule optical driving pulses passing through the waveguide. Specific logic operations depend on the relative pulse strengths and their detunings from an inhomogeneouslly broadened (about 1% for QD transitions centered at 1.5 {mu}m) QD transition. This excitation controlled two-level medium then determines passage of subsequent probe optical pulses. Envelope equations for electromagnetic waves in the linear dispersion and cutoff waveguide modes are derived to simplify solution of the coupled Maxwell-Bloch equations in the waveguide. These determine the quantum mechanical evolution of the QD excitation and its polarization, driven by classical electromagnetic (EM) pulses near a sharp discontinuity in the EM density of states of the bimodal waveguide. Different configurations of the driving pulses lead to distinctive relations between driving pulse strength and probe pulse passage, representing all-optical logic and, or, and not operations. Simulation results demonstrate that such operations can be done on picosecond time scales and within a waveguide length of about 10 {mu}m in a photonic-band-gap (PBG) optical microchip.

  10. Synthesis, structure, and optical properties of colloidal GaN quantum dots

    SciTech Connect (OSTI)

    Micic, O.I.; Ahrenkiel, S.P.; Bertram, D.; Nozik, A.J. [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)] [National Renewable Energy Laboratory, Golden, Colorado 80401 (United States)

    1999-07-01T23:59:59.000Z

    Colloidal chemistry was used to synthesize GaN quantum dots. A GaN precursor, polymeric gallium imide, {l_brace}Ga(NH){sub 3/2}{r_brace}{sub n}, which was prepared by the reaction of dimeric amidogallium with ammonia at room temperature, was heated in trioctylamine at 360&hthinsp;{degree}C for one day to produce GaN nanocrystals. The GaN particles were separated, purified, and partially dispersed in a nonpolar solvent to yield transparent colloidal solutions that consisted of individual GaN particles. The GaN nanocrystals have a spherical shape and mean diameter of about 30{plus_minus}12&hthinsp;{Angstrom}. The spectroscopic behavior of colloidal transparent dispersion has been investigated and shows that the band gap of the GaN nanocrystals shifts to slightly higher energy due to quantum confinement. The photoluminescence spectrum at 10 K (excited at 310 nm) shows band edge emission with several emission peaks in the range between 3.2 and 3.8 eV, while the photoluminescence excitation spectrum shows two excited-state transitions at higher energies. {copyright} {ital 1999 American Institute of Physics.}

  11. Ultrafast single-electron transfer in coupled quantum dots driven by a few-cycle chirped pulse

    SciTech Connect (OSTI)

    Yang, Wen-Xing, E-mail: wenxingyang2@126.com [Department of Physics, Southeast University, Nanjing 210096 (China); Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China); Chen, Ai-Xi [Department of Applied Physics, School of Basic Science, East China Jiaotong University, Nanchang 330013 (China); Bai, Yanfeng [Department of Physics, Southeast University, Nanjing 210096 (China); Lee, Ray-Kuang [Institute of Photonics Technologies, National Tsing-Hua University, Hsinchu 300, Taiwan (China)

    2014-04-14T23:59:59.000Z

    We theoretically study the ultrafast transfer of a single electron between the ground states of a coupled double quantum dot (QD) structure driven by a nonlinear chirped few-cycle laser pulse. A time-dependent Schrödinger equation without the rotating wave approximation is solved numerically. We demonstrate numerically the possibility to have a complete transfer of a single electron by choosing appropriate values of chirped rate parameters and the intensity of the pulse. Even in the presence of the spontaneous emission and dephasing processes of the QD system, high-efficiency coherent transfer of a single electron can be obtained in a wide range of the pulse parameters. Our results illustrate the potential to utilize few-cycle pulses for the excitation in coupled quantum dot systems through the nonlinear chirp parameter control, as well as a guidance in the design of experimental implementation.

  12. Tunable photoluminescence of self-assembled GeSi quantum dots by B{sup +} implantation and rapid thermal annealing

    SciTech Connect (OSTI)

    Chen, Yulu; Wu, Shan; Ma, Yinjie; Fan, Yongliang; Yang, Xinju; Zhong, Zhenyang; Jiang, Zuimin [National Key Laboratory for Surface Physics and Department of Physics, Fudan University, Shanghai 200433 (China)

    2014-06-21T23:59:59.000Z

    The layered GeSi quantum dots (QDs) are grown on (001) Si substrate by molecular beam epitaxy. The photoluminescence (PL) peak of the as-grown GeSi quantum dots has obvious blue shift and enhancement after processed by ion implantation and rapid thermal annealing. It is indicated that the blue shift is originated from the interdiffusion of Ge and Si at the interface between QDs and the surrounding matrix. The dependence of PL intensity on the excitation power shows that there are the nonradiative centers of shallow local energy levels from the point defects caused by the ion implantation, but not removed by the rapid thermal annealing. The tunable blue shift of the PL position from the 1300?nm to 1500?nm region may have significant application value in the optical communication.

  13. Frequency stabilization of the zero-phonon line of a quantum dot via phonon-assisted active feedback

    E-Print Network [OSTI]

    Jack Hansom; Carsten H. H. Schulte; Clemens Matthiesen; Megan Stanley; Mete Atature

    2014-10-17T23:59:59.000Z

    We report on the feedback stabilization of the zero-phonon emission frequency of a single InAs quantum dot. The spectral separation of the phonon-assisted component of the resonance fluorescence provides a probe of the detuning between the zero-phonon transition and the resonant driving laser. Using this probe in combination with active feedback, we stabilize the zero-phonon transition frequency against environmental fluctuations. This protocol reduces the zero-phonon fluorescence intensity noise by a factor of 22 by correcting for environmental noise with a bandwidth of 191 Hz, limited by the experimental collection efficiency. The associated sub-Hz fluctuations in the zero-phonon central frequency are reduced by a factor of 7. This technique provides a means of stabilizing the quantum dot emission frequency without requiring access to the zero-phonon emission.

  14. Periodic arrays of epitaxial self-assembled SiGe quantum dot molecules grown on patterned Si substrates

    SciTech Connect (OSTI)

    Gray, J. L.; Hull, R.; Floro, J. A. [Department of Materials Science and Engineering, University of Pittsburgh, 848 Benedum Hall, Pittsburgh, Pennsylvania 15261 (United States); Sandia National Laboratories, Albuquerque, New Mexico 87185-1415 (United States)

    2006-10-15T23:59:59.000Z

    Ex situ focused ion-beam (FIB) patterning of arrays of holes on Si (001) substrates results in the subsequent formation of SiGe quantum dot molecules at each of the patterned sites during heteroepitaxial growth under kinetically limited growth conditions where island formation is constrained. These quantum dot molecules are fourfold self-assembled island nanostructures bound by a central pit. During growth, material is ejected from the patterned sites forming the pits that in turn provide favorable sites for the cooperative nucleation of (105) faceted islands. The degree of order and quality of the resulting structures depend on many factors including growth temperature, ion-beam milling depth, Si buffer thickness, and spacings between FIB exposed sites. This technique provides a method for controlling the lateral placement of semiconductor nanostructures, which could be used in applications such as complex nanoelectronic architectures.

  15. Fast, High Fidelity Quantum Dot Spin Initialization without a Strong Magnetic Field by Two-Photon Processes

    E-Print Network [OSTI]

    Arka Majumdar; Ziliang Lin; Andrei Faraon; Jelena Vuckovic

    2009-07-20T23:59:59.000Z

    We describe a proposal for fast electron spin initialization in a negatively charged quantum dot coupled to a microcavity without the need for a strong magnetic field. We employ two-photon excitation to access trion states that are spin forbidden by one-photon excitation. Our simulation shows a maximum initialization speed of 1.3 GHz and maximum fidelity of 99.7% with realistic system parameters.

  16. Coulomb interaction of acceptors in Cd{sub 1?x}Mn{sub x}Te/CdTe quantum dot

    SciTech Connect (OSTI)

    Kalpana, P.; Nithiananthi, P., E-mail: kjkumar-gri@rediffmail.com; Jayakumar, K., E-mail: kjkumar-gri@rediffmail.com [Department of Physics, Gandhigram Rural University, Gandhigram-624302, TamilNadu (India); Reuben, A. Merwyn Jasper D. [Department of Physics, School of Engineering, Saveetha University, Thandalam, Chennai- 600104, TamilNadu (India)

    2014-04-24T23:59:59.000Z

    The investigation on the effect of confining potential like isotropic harmonic oscillator type potential on the binding and the Coulomb interaction energy of the double acceptors in the presence of magnetic field in a Cd{sub 1?x}Mn{sub x}Te/CdTe Spherical Quantum Dot has been made for the Mn ion composition x=0.3 and compared with the results obtained from the square well type potential using variational procedure in the effective mass approximation.

  17. Proposal for efficient mode converter based on cavity quantum electrodynamics dark mode in a semiconductor quantum dot coupled to a bimodal microcavity

    SciTech Connect (OSTI)

    Li, Jiahua [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Key Laboratory of Fundamental Physical Quantities Measurement of Ministry of Education, Wuhan 430074 (China); Yu, Rong, E-mail: yurong321@126.com [School of Science, Hubei Province Key Laboratory of Intelligent Robot, Wuhan Institute of Technology, Wuhan 430073 (China); Ma, Jinyong; Wu, Ying, E-mail: yingwu2@163.com [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China)

    2014-10-28T23:59:59.000Z

    The ability to engineer and convert photons between different modes in a solid-state approach has extensive technological implications not only for classical communication systems but also for future quantum networks. In this paper, we put forward a scheme for coherent mode conversion of optical photons by utilizing the intermediate coupling between a single quantum dot and a bimodal photonic crystal microcavity via a waveguide. Here, one mode of the photonic crystal microcavity is coherently driven by an external single-frequency continuous-wave laser field and the two cavity modes are not coupled to each other due to their orthogonal polarizations. The undriven cavity mode is thus not directly coupled to the input driving laser and the only way it can get light is via the quantum dot. The influences of the system parameters on the photon-conversion efficiency are analyzed in detail in the limit of weak probe field and it is found that high photon-conversion efficiency can be achieved under appropriate conditions. It is shown that the cavity dark mode, which is a superposition of the two optical modes and is decoupled from the quantum dot, can appear in such a hybrid optical system. We discuss the properties of the dark mode and indicate that the formation of the dark mode enables the efficient transfer of optical fields between the two cavity modes.

  18. Charge state control in single InAs/GaAs quantum dots by external electric and magnetic fields

    SciTech Connect (OSTI)

    Tang, Jing [Institute of Photo-electronic Thin Film Devices and Technology, Nankai University, Tianjin 300071 (China); Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Cao, Shuo; Gao, Yunan; Sun, Yue; Jin, Kuijuan; Xu, Xiulai, E-mail: xlxu@iphy.ac.cn [Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 (China); Geng, Weidong, E-mail: gengwd@nankai.edu.cn [Institute of Photo-electronic Thin Film Devices and Technology, Nankai University, Tianjin 300071 (China); Williams, David A. [Hitachi Cambridge Laboratory, Cavendish Laboratory, Cambridge CB3 0HE (United Kingdom)

    2014-07-28T23:59:59.000Z

    We report a photoluminescence (PL) spectroscopy study of charge state control in single self-assembled InAs/GaAs quantum dots by applying electric and/or magnetic fields at 4.2?K. Neutral and charged exciton complexes were observed under applied bias voltages from ?0.5?V to 0.5?V by controlling the carrier tunneling. The highly negatively charged exciton emission becomes stronger with increasing pumping power, arising from the fact that electrons have a smaller effective mass than holes and are more easily captured by the quantum dots. The integrated PL intensity of negatively charged excitons is affected significantly by a magnetic field applied along the sample growth axis. This observation is explained by a reduction in the electron drift velocity caused by an applied magnetic field, which increases the probability of non-resonantly excited electrons being trapped by localized potentials at the wetting layer interface, and results in fewer electrons distributed in the quantum dots. The hole drift velocity is also affected by the magnetic field, but it is much weaker.

  19. Fabrication of Diamond Nanowires for Quantum Information Processing Applications

    E-Print Network [OSTI]

    Birgit Hausmann; Mughees Khan; Tom Babinec; Yinan Zhang; Katie Martinick; Murray McCutcheon; Phil Hemmer; Marko Loncar

    2010-02-23T23:59:59.000Z

    We present a design and a top-down fabrication method for realizing diamond nanowires in both bulk single crystal and polycrystalline diamond. Numerical modeling was used to study coupling between a Nitrogen Vacancy (NV) color center and optical modes of a nanowire, and to find an optimal range of nanowire diameters that allows for large collection efficiency of emitted photons. Inductively coupled plasma (ICP) reactive ion etching (RIE) with oxygen is used to fabricate the nanowires. Drop-casted nanoparticles (including $\\mathrm{Au}$, $\\mathrm{SiO_{2}}$ and $\\mathrm{Al_2O_3}$) as well as electron beam lithography defined spin-on glass and evaporated $\\mathrm{Au}$ have been used as an etch mask. We found $\\mathrm{Al_2O_3}$ nanoparticles to be the most etch resistant. At the same time FOx e-beam resist (spin-on glass) proved to be a suitable etch mask for fabrication of ordered arrays of diamond nanowires. We were able to obtain nanowires with near vertical sidewalls in both polycrystalline and single crystal diamond. The heights and diameters of the polycrystalline nanowires presented in this paper are $\\unit[\\approx1]{\\mu m}$ and $\\unit[120-340]{nm}$, respectively, having a $\\unit[200]{nm/min}$ etch rate. In the case of single crystal diamond (types Ib and IIa) nanowires the height and diameter for different diamonds and masks shown in this paper were $\\unit[1-2.4]{\\mu m}$ and $\\unit[120-490]{nm}$ with etch rates between $\\unit[190-240]{nm/min}$.

  20. Built-in electric field and radiative efficiency of polar (0001) and semipolar (11–22) Al{sub 0.5}Ga{sub 0.5}N/GaN quantum dots

    SciTech Connect (OSTI)

    Brault, J.; Kahouli, A.; Leroux, M.; Damilano, B.; Elmaghraoui, D.; Vennéguès, P.; Guillet, T.; Brimont, C. [Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications, CNRS, Rue B.Grégory 06560 Valbonne (France); Laboratoire de Physique de la Matière Condensée, Faculté des Sciences de Tunis, 2092 El Manar (Tunisia)

    2013-12-04T23:59:59.000Z

    We compare the optical properties of ensembles of polar (0001) and semipolar (11–22) Al{sub 0.5}Ga{sub 0.5}N/GaN quantum dots grown by molecular beam epitaxy The polar quantum dot emission shows a huge Stark shift. Using dot height distributions measured by transmission electron microscopy, a simple model allows accounting for the PL energies and lineshapes, and to the screening of the Stark field. The semipolar quantum dots emission show a much weaker Stark effect. High room temperature quantum yields attest the efficiency of 3D-confinement.

  1. Design of 4-electrode optical device for application of vector electric fields to self-assembled quantum dot complexes

    SciTech Connect (OSTI)

    Zhou, Xinran; Doty, Matthew, E-mail: doty@udel.edu [University of Delaware, Newark, Delaware 19716 (United States)

    2014-10-28T23:59:59.000Z

    Self-assembled InAs quantum dots (QDs) are of great interest as components of optoelectronic devices that can operate at the quantum limit. The charge configuration, interdot coupling, and symmetry of complexes containing multiple QDs can all be tuned with applied electric fields, but the magnitude and angle of the electric field required to control each of these parameters depend on the orientation of the QD complex. We present a 4-electrode device compatible with optical excitation and emission that allows application of electric fields with arbitrary magnitudes and angles relative to isolated QD complexes. We demonstrate the electric field tunability of this device with numerical simulations.

  2. A Light-Matter Interface based on a Single InAs/GaAs Quantum Dot in a Nanometallic Cavity

    E-Print Network [OSTI]

    Thomas M. Babinec; Yousif A. Kelaita; Kevin A. Fischer; Konstantinos G. Lagoudakis; Tomas Sarmiento; Armand Rundquist; Arka Majumdar; Jelena Vuckovic

    2014-06-27T23:59:59.000Z

    Progress in solid-state optical cavities is tracked on a timeline of miniaturization. Here, we demonstrate a coupled emitter-cavity system consisting of an InAs/GaAs Quantum Dot embedded in a hybrid metal/semiconductor nanocavity. Key features of our nanometallic light-matter interface include: (i) order of magnitude reduction in mode volume compared to that of leading photonic crystal cQED systems, resulting in maximum atom-field coupling rate g/(2{\\pi})~180GHz; (ii) surface-emitting nanocylinder geometry and therefore good collection efficiency compared to the bulk (~5X enhancement); (iii) strong and broadband spontaneous emission rate enhancement (Purcell factor ~8); and finally (iv) the ability to efficiently optically address a multi-level quantum emitter based on a charged quantum dot inside the nanocavity. This light-matter interface could play an important role in studies of the cavity quantum electrodynamics as well as in its application to optical interconnects and quantum networks.

  3. Exchange Interaction Between Three and Four Coupled Quantum Dots: Theory and Applications to Quantum Computing

    E-Print Network [OSTI]

    Ari Mizel; Daniel A. Lidar

    2004-01-22T23:59:59.000Z

    Several prominent proposals have suggested that spins of localized electrons could serve as quantum computer qubits. The exchange interaction has been invoked as a means of implementing two qubit gates. In this paper, we analyze the strength and form of the exchange interaction under relevant conditions. We find that, when several spins are engaged in mutual interactions, the quantitative strengths or even qualitative forms of the interactions can change. It is shown that the changes can be dramatic within a Heitler-London model. Hund-Mulliken calculations are also presented, and support the qualititative conclusions from the Heitler-London model. The effects need to be considered in spin-based quantum computer designs, either as a source of gate error to be overcome or a new interaction to be exploited.

  4. ThermoElectric Transport Properties of a Chain of Quantum Dots with Self-Consistent Reservoirs

    E-Print Network [OSTI]

    Philippe A. Jacquet

    2009-02-13T23:59:59.000Z

    We introduce a model for charge and heat transport based on the Landauer-Buttiker scattering approach. The system consists of a chain of $N$ quantum dots, each of them being coupled to a particle reservoir. Additionally, the left and right ends of the chain are coupled to two particle reservoirs. All these reservoirs are independent and can be described by any of the standard physical distributions: Maxwell-Boltzmann, Fermi-Dirac and Bose-Einstein. In the linear response regime, and under some assumptions, we first describe the general transport properties of the system. Then we impose the self-consistency condition, i.e. we fix the boundary values (T_L,\\mu_L) and (T_R,mu_R), and adjust the parameters (T_i,mu_i), for i = 1,...,N, so that the net average electric and heat currents into all the intermediate reservoirs vanish. This condition leads to expressions for the temperature and chemical potential profiles along the system, which turn out to be independent of the distribution describing the reservoirs. We also determine the average electric and heat currents flowing through the system and present some numerical results, using random matrix theory, showing that these currents are typically governed by Ohm and Fourier laws.

  5. Effect of graphene on photoluminescence properties of graphene/GeSi quantum dot hybrid structures

    SciTech Connect (OSTI)

    Chen, Y. L.; Ma, Y. J.; Wang, W. Q.; Ding, K.; Wu, Q.; Fan, Y. L.; Yang, X. J.; Zhong, Z. Y.; Jiang, Z. M., E-mail: zmjiang@fudan.edu.cn [State Key Laboratory of Surface Physics, Key Laboratory of Micro and Nano Photonic Structures (Ministry of Education) and Department of Physics, Fudan University, Shanghai 200433 (China); Chen, D. D.; Xu, F. [SHU-SolarE R and D Lab, Department of Physics, College of Science, Shanghai University, Shanghai 200444 (China)

    2014-07-14T23:59:59.000Z

    Graphene has been discovered to have two effects on the photoluminescence (PL) properties of graphene/GeSi quantum dot (QD) hybrid structures, which were formed by covering monolayer graphene sheet on the multilayer ordered GeSi QDs sample surfaces. At the excitation of 488?nm laser line, the hybrid structure had a reduced PL intensity, while at the excitation of 325?nm, it had an enhanced PL intensity. The attenuation in PL intensity can be attributed to the transferring of electrons from the conducting band of GeSi QDs to the graphene sheet. The electron transfer mechanism was confirmed by the time resolved PL measurements. For the PL enhancement, a mechanism called surface-plasmon-polariton (SPP) enhanced absorption mechanism is proposed, in which the excitation of SPP in the graphene is suggested. Due to the resonant excitation of SPP by incident light, the absorption of incident light is much enhanced at the surface region, thus leading to more exciton generation and a PL enhancement in the region. The results may be helpful to provide us a way to improve optical properties of low dimensional surface structures.

  6. Improvement of the quality of graphene-capped InAs/GaAs quantum dots

    SciTech Connect (OSTI)

    Othmen, Riadh, E-mail: othmenriadh@yahoo.fr; Rezgui, Kamel; Ajlani, Hosni; Oueslati, Meherzi [Faculté des Sciences de Tunis, Université de Tunis El Manar, Campus, 2092 El Manar Tunis (Tunisia); Cavanna, Antonella; Madouri, Ali [CNRS/LPN, Route de Nozay, F-91460 Marcoussis (France); Arezki, Hakim; Gunes, Fethullah [Laboratoire de Génie Electrique de Paris, 11, rue Joliot Curie Plateau de Moulon, 91192 Gif sur Yvette (France)

    2014-06-07T23:59:59.000Z

    In this paper, we study the transfer of graphene onto InAs/GaAs quantum dots (QDs). The graphene is first grown on Cu foils by chemical vapor deposition and then polymer Polymethyl Methacrylate (PMMA) is deposited on the top of graphene/Cu. High quality graphene sheet has been obtained by lowering the dissolving rate of PMMA using vapor processing. Uncapped as well as capped graphene InAs/GaAs QDs have been studied using optical microscopy, scanning electron microscopy, and Raman spectroscopy. We gather from this that the average shifts ?? of QDs Raman peaks are reduced compared to those previously observed in graphene and GaAs capped QDs. The encapsulation by graphene makes the indium atomic concentration intact in the QDs by the reduction of the strain effect of graphene on QDs and the migration of In atoms towards the surface. This gives us a new hetero-structure graphene–InAs/GaAs QDs wherein the graphene plays a key role as a cap layer.

  7. Ultrafast Manipulation of a Double Quantum Dot via Lyapunov Control Method

    E-Print Network [OSTI]

    Shuang Cong; Ming-yong Gao; Long-zhen Hu; Guo-ping Guo; Gang Cao; Guang-can Guo

    2014-01-12T23:59:59.000Z

    For a double quantum dot (DQD) system, here we propose alternative ultrafast manipulate approach: Lyapunov control method, to transfer the state from R to L on the picosecond scale, orders of magnitude faster and transfer probability higher than the previously measured electrically controlled charge- or spin-based quits. The control laws are composed of two-direction components, one is used to eliminate the dissipation in the system, another is used to transfer the state. The control theory's stability ensures the system can be transferred to the target state in high probability, and the coefficients in control laws leads very fast convergence. The role of eliminating the dissipation plays the suppression of decoherence effect. Numerical simulation results show that under the realistic implementation conditions, the transfer probability and fidelity can be increased up to 98.79% and 98.97%, respectively. This is the first result directly applicable to a DQD system's state transferring using the Lyapunov control method. We also give specific experimental realization scheme.

  8. Electron-correlation driven capture and release in double quantum dots

    E-Print Network [OSTI]

    Federico M. Pont; Annika Bande; Lorenz S. Cederbaum

    2014-12-29T23:59:59.000Z

    We recently predicted that the interatomic Coulombic electron capture (ICEC) process, a long-range electron correlation driven capture process, is achievable in gated double quantum dots (DQDs) [F. M. Pont, A. Bande, L. S. Cederbaum, Phys. Rev. B {\\bf 88} 241304(R)(2013)]. In ICEC an incoming electron is captured by one QD and the excess energy is used to remove an electron from the neighboring QD. In this work we present systematic full three-dimensional electron dynamics calculations in quasi-one dimensional model potentials that allow for a detailed understanding of the connection between the DQD geometry and the reaction probability for the ICEC process. Investigation of the electronic structure of various DQD geometries that are capable of undergoing the ICEC process clarify the offspring of its remarkably high probability in the presence of two electron resonances. The quasi-one dimensional geometry allows to construct an effective one-dimensional model whose results compare very well with those obtained using the full calculations.

  9. Blinking effect and the use of quantum dots in single molecule spectroscopy

    SciTech Connect (OSTI)

    Rombach-Riegraf, Verena; Oswald, Peter; Bienert, Roland; Petersen, Jan [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany)] [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany); Domingo, M.P. [Instituto de Carboquimica (CSIC), Miguel Luesma 4, 50018 Zaragoza (Spain)] [Instituto de Carboquimica (CSIC), Miguel Luesma 4, 50018 Zaragoza (Spain); Pardo, Julian [Grupo Apoptosis, Inmunidad y Cancer, Departamento Bioquimica y Biologia Molecular y Celular, Fac. Ciencias, Universidad de Zaragoza, Zaragoza (Spain) [Grupo Apoptosis, Inmunidad y Cancer, Departamento Bioquimica y Biologia Molecular y Celular, Fac. Ciencias, Universidad de Zaragoza, Zaragoza (Spain); Fundacion Aragon I-D (ARAID), Gobierno de Aragon, Zaragoza (Spain); Immune Effector Cells Group, Aragon Health Research Institute (IIS Aragon), Biomedical Research Centre of Aragon (CIBA) Fundacion Aragon I-D - ARAID, Gobierno de Aragon, Zaragoza (Spain); Graeber, P. [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany)] [Albert-Ludwigs-Universitaet Freiburg, Institut fuer Physikalische Chemie, Albertstrasse 23a, 79104 Freiburg (Germany); Galvez, E.M., E-mail: eva@icb.csic.es [Instituto de Carboquimica (CSIC), Miguel Luesma 4, 50018 Zaragoza (Spain); Immune Effector Cells Group, Aragon Health Research Institute (IIS Aragon), Biomedical Research Centre of Aragon (CIBA) Fundacion Aragon I-D - ARAID, Gobierno de Aragon, Zaragoza (Spain)

    2013-01-04T23:59:59.000Z

    Highlights: Black-Right-Pointing-Pointer It is possible to eliminate the blinking effect of a water-soluble QD. Black-Right-Pointing-Pointer We provide a direct method to study protein function and dynamics at the single level. Black-Right-Pointing-Pointer QD, potent tool for single molecule studies of biochemical and biological processes. -- Abstract: Luminescent semiconductor nanocrystals (quantum dots, QD) have unique photo-physical properties: high photostability, brightness and narrow size-tunable fluorescence spectra. Due to their unique properties, QD-based single molecule studies have become increasingly more popular during the last years. However QDs show a strong blinking effect (random and intermittent light emission), which may limit their use in single molecule fluorescence studies. QD blinking has been widely studied and some hypotheses have been done to explain this effect. Here we summarise what is known about the blinking effect in QDs, how this phenomenon may affect single molecule studies and, on the other hand, how the 'on'/'off' states can be exploited in diverse experimental settings. In addition, we present results showing that site-directed binding of QD to cysteine residues of proteins reduces the blinking effect. This option opens a new possibility of using QDs to study protein-protein interactions and dynamics by single molecule fluorescence without modifying the chemical composition of the solution or the QD surface.

  10. Heat generation by electronic current in a quantum dot spin-valve

    SciTech Connect (OSTI)

    Chi, Feng [School of Physical Science and Technology, Inner Mongolia University, Huhehaote 010023 (China); College of Engineering, Bohai University, Jinzhou 121013 (China); Sun, Lian-Liang [College of Science, North China University of Technology, Beijing 100041 (China); Guo, Yu [College of Engineering, Bohai University, Jinzhou 121013 (China)

    2014-10-28T23:59:59.000Z

    Electric-current-induced heat generation in an interacting single-level quantum dot connected to ferromagnetic leads with noncollinear magnetizations is theoretically investigated. We find that when the two leads' spin polarization rates are identical and much smaller than unit, the magnitude of the heat generation is almost monotonously enhanced as the angle between the leads' magnetic moments is varied from zero to ?, while the magnitude of the electric current is continuously suppressed. Moreover, the properties of the heat generation depend on the lead's spin polarization rate in different ways when the angle is varied. If at least one of the leads' spin polarization rate approaches to unit, the spin-valve effect of the heat generation is identical to that of the electric current. Now the previously found negative differential of the heat generation disappears when the angle approaches to ?. As compared to the current, the heat generation is more sensitive to the system's asymmetry when one of the electrodes is half-metallic in noncollinear configurations.

  11. Ultra-low threshold, electrically pumped quantum dot photonic crystal nanocavity laser

    E-Print Network [OSTI]

    Bryan Ellis; Marie Mayer; Gary Shambat; Tomas Sarmiento; James Harris; Eugene Haller; Jelena Vuckovic

    2011-05-02T23:59:59.000Z

    Efficient, low threshold, and compact semiconductor laser sources are being investigated for many applications in high-speed communications, information processing, and optical interconnects. The best edge-emitting and vertical cavity surface-emitting lasers (VCSELs) have thresholds on the order of 100 \\muA[1,2] but dissipate too much power to be practical for many applications, particularly optical interconnects[3]. Optically pumped photonic crystal (PC) nanocavity lasers represent the state of the art in low-threshold lasers[4,5]; however, in order to be practical, techniques to electrically pump these structures must be developed. Here we demonstrate a quantum dot photonic crystal nanocavity laser in gallium arsenide pumped by a lateral p-i-n junction formed by ion implantation. Continuous wave lasing is observed at temperatures up to 150 K. Thresholds of only 181 nA at 50 K and 287 nA at 150 K are observed - the lowest thresholds ever observed in any type of electrically pumped laser.

  12. Growth of silicon quantum dots by oxidation of the silicon nanocrystals embedded within silicon carbide matrix

    SciTech Connect (OSTI)

    Kole, Arindam; Chaudhuri, Partha, E-mail: erpc@iacs.res.in [Indian Association for the Cultivation of Science, 2A and 2B Raja S.C. Mullick Road, Jadavpur, Kolkata-700032 (India)

    2014-10-15T23:59:59.000Z

    A moderately low temperature (?800 °C) thermal processing technique has been described for the growth of the silicon quantum dots (Si-QD) within microcrystalline silicon carbide (?c-SiC:H) dielectric thin films deposited by plasma enhanced chemical vapour deposition (PECVD) process. The nanocrystalline silicon grains (nc-Si) present in the as deposited films were initially enhanced by aluminium induced crystallization (AIC) method in vacuum at a temperature of T{sub v} = 525 °C. The samples were then stepwise annealed at different temperatures T{sub a} in air ambient. Analysis of the films by FTIR and XPS reveal a rearrangement of the ?c-SiC:H network has taken place with a significant surface oxidation of the nc-Si domains upon annealing in air. The nc-Si grain size (D{sub XRD}) as calculated from the XRD peak widths using Scherrer formula was found to decrease from 7 nm to 4 nm with increase in T{sub a} from 250 °C to 800 °C. A core shell like structure with the nc-Si as the core and the surface oxide layer as the shell can clearly describe the situation. The results indicate that with the increase of the annealing temperature in air the oxide shell layer becomes thicker and the nc-Si cores become smaller until their size reduced to the order of the Si-QDs. Quantum confinement effect due to the SiO covered nc-Si grains of size about 4 nm resulted in a photoluminescence peak due to the Si QDs with peak energy at 1.8 eV.

  13. Biexciton recombination rates in self-assembled quantum dots Michael Wimmer,1, 2,

    E-Print Network [OSTI]

    Shumway, John

    GaAs/GaAs, CdSe/ZnSe, and InP/InGaP dots are evaluated, including anisotropic effective masses. Depending

  14. A quasinormal mode approach to the local-field problem in quantum optics: applications to quantum-dot nanoplasmonic systems

    E-Print Network [OSTI]

    Ge, Rong-Chun; Hughes, S

    2015-01-01T23:59:59.000Z

    The local-field (LF) problem of a finite-size dipole emitter radiating inside a lossy inhomogeneous structure is a longstanding and challenging quantum optical problem, and now is becoming more important due to rapid advances in solid-state fabrication technologies. Here we introduce a simple and accurate quasi-normal mode (QNM) technique to solve this problem analytically by separating the scattering problem into contributions from the QNM and an image dipole. Using a real-cavity model to describe an artificial atom inside a lossy and dispersive gold nanorod, we show when the contribution of the QNM to LFs will dominate over the homogeneous contribution. We also show how to accurately describe surface scattering for real cavities that are close to the metal interface, and explore regimes when the surface scattering also dominates. Our results offer an intuitive picture of the underlying physics for the LF problem and facilitate the understanding of novel photon sources within lossy structures.

  15. 1810 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 33, NO. 10, OCTOBER 1997 Design, Fabrication, and Performance of Infrared

    E-Print Network [OSTI]

    1810 IEEE JOURNAL OF QUANTUM ELECTRONICS, VOL. 33, NO. 10, OCTOBER 1997 Design, Fabrication selective oxidation and visible wave- length operation. Index Terms-- Optoelectronic devices, semiconductor device fabrication, semiconductor lasers. I. INTRODUCTION IN THE 1970's, Iga et al. at the Tokyo

  16. PMMA quantum dots composites fabricated via use of pre-polymerization

    E-Print Network [OSTI]

    Fainman, Yeshaiahu

    . Alivisatos, "Light-emitting diodes made from cadmium selenide nanocrystals and a semiconducting polymer," Nature 370 354­357 (1994). 4. M. Bruchez, M. Moronne, P. Gin, S. Weiss, A. P. Alivisatos, "Semiconductor. Phys. Chem. 100, 468­471 (1996). 14. M. C. Schlamp, X. G. Peng, A. P. Alivisatos, "Improved

  17. Silicon And Silicon-germanium Epitaxy For Quantum Dot Device Fabrications

    E-Print Network [OSTI]

    as they provide highly tunable structures for trapping and manipu- lating individual electrons/silicon- germanium material heterosystem. We describe the growth of two-dimensional electron gas structures advisor Professor James C. Sturm, whose perpetual enthusiasm, stimulating insight, and constant

  18. Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

    SciTech Connect (OSTI)

    McKerracher, Ian; Fu Lan; Hoe Tan, Hark; Jagadish, Chennupati [Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

    2012-12-01T23:59:59.000Z

    Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiO{sub x}N{sub y} films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

  19. Enhancement of current collection in epitaxial lift-off InAs/GaAs quantum dot thin film solar cell and concentrated photovoltaic study

    SciTech Connect (OSTI)

    Sogabe, Tomah, E-mail: sogabe@mbe.rcast.u-tokyo.ac.jp; Shoji, Yasushi; Tamayo, Efrain; Okada, Yoshitaka [Research Center for Advanced Science and Technology (RCAST), The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8504 (Japan); Mulder, Peter; Schermer, John [Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen (Netherlands)

    2014-09-15T23:59:59.000Z

    We report the fabrication of a thin film InAs/GaAs quantum dot solar cell (QD cell) by applying epitaxial lift-off (ELO) approach to the GaAs substrate. We confirmed significant current collection enhancement (?0.91?mA/cm{sup 2}) in the ELO-InAs QD cell within the wavelength range of 700?nm–900?nm when compared to the ELO-GaAs control cell. This is almost six times of the sub-GaAs bandgap current collection (?0.16?mA/cm{sup 2}) from the wavelength range of 900?nm and beyond, we also confirmed the ELO induced resonance cavity effect was able to increase the solar cell efficiency by increasing both the short circuit current and open voltage. The electric field intensity of the resonance cavity formed in the ELO film between the Au back reflector and the GaAs front contact layer was analyzed in detail by finite-differential time-domain (FDTD) simulation. We found that the calculated current collection enhancement within the wavelength range of 700?nm–900?nm was strongly influenced by the size and shape of InAs QD. In addition, we performed concentrated light photovoltaic study and analyzed the effect of intermediate states on the open voltage under varied concentrated light intensity for the ELO-InAs QD cell.

  20. Interface effect of InSb quantum dots embedded in SiO{sub 2} matrix

    SciTech Connect (OSTI)

    Chen Dongliang; Fan Jiangwei; Wei Shiqiang [National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 (China); Li Chaosheng; Zhu Zhengang [Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, PO Box 1129, Hefei 230031 (China)

    2005-08-15T23:59:59.000Z

    The interface effect of InSb quantum dots (QDs) embedded in SiO{sub 2} matrix has been investigated by Raman scattering spectroscopy, x-ray diffraction (XRD), and x-ray absorption fine structure (both of EXAFS and XANES). The EXAFS and XRD results show clearly that the bond length of the Sb-In first shell of the InSb QDs contracts slightly about 0.02 A compared with that of the bulk InSb. The Raman scattering spectrum of the InSb QDs reveals that the lattice contraction partly weakens the phonon confinement effect. The coordination geometry at the interface of the InSb QDs is mainly Sb (In)-O covalent bridge bonds. The Sb K-XANES calculations of InSb QDs embedded in SiO{sub 2} matrix based on FEFF8 indicate that the intensity increase and the broadening of the white line peak of Sb atoms are essentially attributed to both the increase of Sb p-hole population and the change of Sb intra-atomic potential {mu}{sub 0}(E) affected by the SiO{sub 2} matrix. Our results show that the interface effect between the InSb QDs and the SiO{sub 2} matrix leads not only to the slight lattice contraction of InSb QDs and the large structural distortion in the interface area of InSb QDs, but also to the significant change of the Sb intra-atomic potential and the obvious charge redistribution around Sb atoms.

  1. SiGe quantum dot molecules grown on patterned Si (001) substrates

    SciTech Connect (OSTI)

    Yang Hongbin; Zhang Xiangjiu; Jiang Zuiming; Yang Xinju; Fan Yongliang [Surface Physics Laboratory (National Key Laboratory), Fudan University, Shanghai 200433 (China)

    2008-08-15T23:59:59.000Z

    SiGe quantum dot molecules (QDMs) grown on patterned Si (001) substrates by molecular beam epitaxy were studied. Experimental results showed that the density, the dimension, and the dimension distribution of the SiGe QDMs grown in the windows were dependent on the window size. When the thickness of the Si{sub 0.8}Ge{sub 0.2} film was 40 nm, QDMs only appeared in the unpatterned areas of the Si substrate and none could be found inside the windows of 6x6 {mu}m{sup 2} on the same substrate. However, when the thickness of Si{sub 0.8}Ge{sub 0.2} film was increased to 80 nm, QDMs appeared both inside the windows and in the unpatterned areas, and the density of QDMs was reduced with the decrease in the window size. We attribute these results to the different strain relaxations in different size windows, which are caused by the edge effect of the epitaxial film in the window. Based on these experimental results we discuss the formation and the size stability of the QDMs and conclude that the formation of the SiGe QDM originates from an intrinsic cause of the strain relief mechanism. This work also shows that by means of the edge induced strain relaxation of the epitaxial film in the window, it is possible to reveal the influence of the strain on some physical properties of the SiGe film without changing its Ge atomic fraction.

  2. Pulsed Electrical Spin Injection into InGaAs Quantum Dots: Studies of the Electroluminescence Polarization Dynamics

    SciTech Connect (OSTI)

    Asshoff, P.; Loeffler, W.; Fluegge, H.; Zimmer, J.; Mueller, J.; Westenfelder, B.; Hu, D. Z.; Schaadt, D. M.; Kalt, H.; Hetterich, M. [Institut fuer Angewandte Physik and DFG Center for Functional Nanostructures (CFN), Universitaet Karlsruhe, 76131 Karlsruhe (Germany)

    2010-01-04T23:59:59.000Z

    We present time-resolved studies of the spin polarization dynamics during and after initialization through pulsed electrical spin injection into InGaAs quantum dots embedded in a p-i-n-type spin-injection light-emitting diode. Experiments are performed with pulse widths in the nanosecond range and a time-resolved single photon counting setup is used to detect the subsequent electroluminescence. We find evidence that the achieved spin polarization shows an unexpected temporal behavior, attributed mainly to many-carrier and non-equilibrium effects in the device.

  3. Bound state energies and wave functions of spherical quantum dots in presence of a confining potential model

    E-Print Network [OSTI]

    Sameer M. Ikhdair

    2011-10-03T23:59:59.000Z

    We obtain the exact energy spectra and corresponding wave functions of the radial Schr\\"odinger equation (RSE) for any (n,l) state in the presence of a combination of psudoharmonic, Coulomb and linear confining potential terms using an exact analytical iteration method. The interaction potential model under consideration is Cornell-modified plus harmonic (CMpH) type which is a correction form to the harmonic, Coulomb and linear confining potential terms. It is used to investigates the energy of electron in spherical quantum dot and the heavy quarkonia (QQ-onia).

  4. Self-organized arrays of graphene and few-layer graphene quantum dots in fluorographene matrix: Charge transient spectroscopy

    SciTech Connect (OSTI)

    Antonova, Irina V., E-mail: antonova@isp.nsc.ru [Rzhanov Institute of Semiconductor Physics, SB RAS, Lavrentiev Avenue 13, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Pirogov st. 2, Novosibirsk 630090 (Russian Federation); Nebogatikova, Nadezhda A.; Prinz, Victor Ya. [Rzhanov Institute of Semiconductor Physics, SB RAS, Lavrentiev Avenue 13, Novosibirsk 630090 (Russian Federation)

    2014-05-12T23:59:59.000Z

    Arrays of graphene or few-layer graphene quantum dots (QDs) embedded in a partially fluorinated graphene matrix were created by chemical functionalization of layers. Charge transient spectroscopy employed for investigation of obtained QD systems (size 20–70 nm) has allowed us to examine the QD energy spectra and the time of carrier emission (or charge relaxation) from QDs as a function of film thickness. It was found that the characteristic time of carrier emission from QDs decreased markedly (by about four orders of magnitude) on increasing the QD thickness from one graphene monolayer to 3 nm. Daylight-assisted measurements also demonstrate a strong decrease of the carrier emission time.

  5. Efficient, air-stable colloidal quantum dot solar cells encapsulated using atomic layer deposition of a nanolaminate barrier

    SciTech Connect (OSTI)

    Ip, Alexander H.; Labelle, André J.; Sargent, Edward H., E-mail: ted.sargent@utoronto.ca [Department of Electrical and Computer Engineering, University of Toronto, 10 King's College Road, Toronto, Ontario M5S 3G4 (Canada)

    2013-12-23T23:59:59.000Z

    Atomic layer deposition was used to encapsulate colloidal quantum dot solar cells. A nanolaminate layer consisting of alternating alumina and zirconia films provided a robust gas permeation barrier which prevented device performance degradation over a period of multiple weeks. Unencapsulated cells stored in ambient and nitrogen environments demonstrated significant performance losses over the same period. The encapsulated cell also exhibited stable performance under constant simulated solar illumination without filtration of harsh ultraviolet photons. This monolithically integrated thin film encapsulation method is promising for roll-to-roll processed high efficiency nanocrystal solar cells.

  6. Influence of GaAs surface termination on GaSb/GaAs quantum dot structure and band offsets

    SciTech Connect (OSTI)

    Zech, E. S.; Chang, A. S.; Martin, A. J.; Canniff, J. C.; Millunchick, J. M. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Lin, Y. H. [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)] [Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Goldman, R. S. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States) [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109-2136 (United States)

    2013-08-19T23:59:59.000Z

    We have investigated the influence of GaAs surface termination on the nanoscale structure and band offsets of GaSb/GaAs quantum dots (QDs) grown by molecular-beam epitaxy. Transmission electron microscopy reveals both coherent and semi-coherent clusters, as well as misfit dislocations, independent of surface termination. Cross-sectional scanning tunneling microscopy and spectroscopy reveal clustered GaSb QDs with type I band offsets at the GaSb/GaAs interfaces. We discuss the relative influences of strain and QD clustering on the band offsets at GaSb/GaAs interfaces.

  7. Validity of the single-particle description and charge noise resilience for multi-electron quantum dots

    E-Print Network [OSTI]

    Michiel A. Bakker; Sebastian Mehl; Tuukka Hiltunen; Ari Harju; David P. DiVincenzo

    2015-02-11T23:59:59.000Z

    We construct an optimal set of single-particle states for few-electron quantum dots (QDs) using the method of natural orbitals (NOs). The NOs include also the effects of the Coulomb repulsion between electrons. We find that they agree well with the noniteracting orbitals for GaAs QDs of realistic parameters, while the Coulomb interactions only rescale the radius of the NOs compared to the noninteracting case. We use NOs to show that four-electron QDs are less susceptible to charge noise than their two-electron counterparts.

  8. Growth-temperature dependence of optical spin-injection dynamics in self-assembled InGaAs quantum dots

    SciTech Connect (OSTI)

    Yamamura, Takafumi; Kiba, Takayuki; Yang, Xiaojie; Takayama, Junichi; Subagyo, Agus; Sueoka, Kazuhisa; Murayama, Akihiro, E-mail: murayama@ist.hokudai.ac.jp [Graduate School of Information Science and Technology, Hokkaido University, Kita 14, Nishi 9, Kita-ku, Sapporo 060-0814 (Japan)

    2014-09-07T23:59:59.000Z

    The growth-temperature dependence of the optical spin-injection dynamics in self-assembled quantum dots (QDs) of In{sub 0.5}Ga{sub 0.5}As was studied by increasing the sheet density of the dots from 2?×?10{sup 10} to 7?×?10{sup 10}?cm{sup ?2} and reducing their size through a decrease in growth temperature from 500 to 470?°C. The circularly polarized transient photoluminescence (PL) of the resulting QD ensembles was analyzed after optical excitation of spin-polarized carriers in GaAs barriers by using rate equations that take into account spin-injection dynamics such as spin-injection time, spin relaxation during injection, spin-dependent state-filling, and subsequent spin relaxation. The excitation-power dependence of the transient circular polarization of PL in the QDs, which is sensitive to the state-filling effect, was also examined. It was found that a systematic increase occurs in the degree of circular polarization of PL with decreasing growth temperature, which reflects the transient polarization of exciton spin after spin injection. This is attributed to strong suppression of the filling effect for the majority-spin states as the dot-density of the QDs increases.

  9. SU(4) Kondo Effect in Carbon Nanotube Quantum Dots: Kondo Effect without Charge Quantization

    E-Print Network [OSTI]

    Finkelstein, Gleb

    for 1 electron: Double dots, dots with symmetries: D. Boese et al., PRB (2002) L. Borda et al., PRL (2003) K. Le Hur and P. Simon, PRB (2003) G. Zarand et al., SSC (2003) W. Izumida et al., J.R. Krishnamurthy, PRL (2005) C.A. Busser and G.B. Martins, PRB (2007) 2-e Kondo in nanotubes ­ triplet or SU(4) W

  10. Nonlinear optical spectra having characteristics of Fano interferences in coherently coupled lowest exciton biexciton states in semiconductor quantum dots

    SciTech Connect (OSTI)

    Gotoh, Hideki, E-mail: gotoh.hideki@lab.ntt.co.jp; Sanada, Haruki; Yamaguchi, Hiroshi; Sogawa, Tetsuomi [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato-Wakamiya, Atsugi-shi, Kanagawa 243-0198 (Japan)

    2014-10-15T23:59:59.000Z

    Optical nonlinear effects are examined using a two-color micro-photoluminescence (micro-PL) method in a coherently coupled exciton-biexciton system in a single quantum dot (QD). PL and photoluminescence excitation spectroscopy (PLE) are employed to measure the absorption spectra of the exciton and biexciton states. PLE for Stokes and anti-Stokes PL enables us to clarify the nonlinear optical absorption properties in the lowest exciton and biexciton states. The nonlinear absorption spectra for excitons exhibit asymmetric shapes with peak and dip structures, and provide a distinct contrast to the symmetric dip structures of conventional nonlinear spectra. Theoretical analyses with a density matrix method indicate that the nonlinear spectra are caused not by a simple coherent interaction between the exciton and biexciton states but by coupling effects among exciton, biexciton and continuum states. These results indicate that Fano quantum interference effects appear in exciton-biexciton systems at QDs and offer important insights into their physics.

  11. A carrier relaxation bottleneck probed in single InGaAs quantum dots using integrated superconducting single photon detectors

    SciTech Connect (OSTI)

    Reithmaier, G., E-mail: guenther.reithmaier@wsi.tum.de; Flassig, F.; Hasch, P.; Lichtmannecker, S.; Kaniber, M. [Walter Schottky Institut, Technische Universität München (Germany); Müller, K. [Walter Schottky Institut, Technische Universität München (Germany); E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States); Vu?kovi?, J. [E. L. Ginzton Laboratory, Stanford University, Stanford, California 94305 (United States); TUM Institute of Advanced Study, Lichtenbergstraße 2a, 85748 Garching (Germany); Gross, R. [Walther Meißner Institut, Bayerische Akademie der Wissenschaften, Garching (Germany); Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 München (Germany); Finley, J. J., E-mail: finley@wsi.tum.de [Walter Schottky Institut, Technische Universität München (Germany); Nanosystems Initiative Munich (NIM), Schellingstraße 4, 80799 München (Germany)

    2014-08-25T23:59:59.000Z

    Using integrated superconducting single photon detectors, we probe ultra-slow exciton capture and relaxation dynamics in single self-assembled InGaAs quantum dots embedded in a GaAs ridge waveguide. Time-resolved luminescence measurements performed with on- and off-chip detection reveal a continuous decrease in the carrier relaxation time from 1.22?±?0.07?ns to 0.10?±?0.07?ns upon increasing the number of non-resonantly injected carriers. By comparing off-chip time-resolved spectroscopy with spectrally integrated on-chip measurements, we identify the observed dynamics in the rise time (?{sub r}) as arising from a relaxation bottleneck at low excitation levels. From the comparison with the temporal dynamics of the single exciton transition with the on-chip emission signal, we conclude that the relaxation bottleneck is circumvented by the presence of charge carriers occupying states in the bulk material and the two-dimensional wetting layer continuum. A characteristic ?{sub r} ? P{sup ?2?3} power law dependence is observed suggesting Auger-type scattering between carriers trapped in the quantum dot and the two-dimensional wetting layer continuum which circumvents the phonon relaxation bottleneck.

  12. Quantum dot ternary-valued full-adder: Logic synthesis by a multiobjective design optimization based on a genetic algorithm

    SciTech Connect (OSTI)

    Klymenko, M. V.; Remacle, F., E-mail: fremacle@ulg.ac.be [Department of Chemistry, B6c, University of Liege, B4000 Liege (Belgium)

    2014-10-28T23:59:59.000Z

    A methodology is proposed for designing a low-energy consuming ternary-valued full adder based on a quantum dot (QD) electrostatically coupled with a single electron transistor operating as a charge sensor. The methodology is based on design optimization: the values of the physical parameters of the system required for implementing the logic operations are optimized using a multiobjective genetic algorithm. The searching space is determined by elements of the capacitance matrix describing the electrostatic couplings in the entire device. The objective functions are defined as the maximal absolute error over actual device logic outputs relative to the ideal truth tables for the sum and the carry-out in base 3. The logic units are implemented on the same device: a single dual-gate quantum dot and a charge sensor. Their physical parameters are optimized to compute either the sum or the carry out outputs and are compatible with current experimental capabilities. The outputs are encoded in the value of the electric current passing through the charge sensor, while the logic inputs are supplied by the voltage levels on the two gate electrodes attached to the QD. The complex logic ternary operations are directly implemented on an extremely simple device, characterized by small sizes and low-energy consumption compared to devices based on switching single-electron transistors. The design methodology is general and provides a rational approach for realizing non-switching logic operations on QD devices.

  13. Surface Plasmon-Quantum Dot Coupling from Arrays of Nanoholes Alexandre G. Brolo,*, Shing C. Kwok, Matthew D. Cooper, Matthew G. Moffitt,*,

    E-Print Network [OSTI]

    Brolo, Alexandre G.

    Surface Plasmon-Quantum Dot Coupling from Arrays of Nanoholes Alexandre G. Brolo,*, Shing C. Kwok) to the surface plasmon (SP) modes of nanohole arrays in a metal film was demonstrated for the first time, showing in the SP-QD system is promising for prospective plasmonic light-emitting devices incorporating QDs. 1

  14. HaloTag protein-mediated specific labeling of living cells with quantum dots Min-kyung So, Hequan Yao 1

    E-Print Network [OSTI]

    Rao, Jianghong

    ], peptides [19­20], or nucleic acids [21], fol- lowed by further functionalization with biorecognition step with quantum dot conjugates that are functionalized with HaloTag ligand, or in two steps on the size of the nanoparticles--larger size produces longer emission wave- length [10]. All these potential

  15. arXiv:1007.2404v1[cond-mat.mes-hall]14Jul2010 Electrostatically defined Quantum Dots in a Si/SiGe

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    arXiv:1007.2404v1[cond-mat.mes-hall]14Jul2010 Electrostatically defined Quantum Dots in a Si/SiGe (QD) realized in a molecular beam epitaxy grown Si/SiGe heterostructure. Transport and charge as a spin qubit. Our results promise the suitability of electrostatically defined QDs in Si/SiGe

  16. The emission of polarized light from GaN/AlN self-assembled quantum dots subject to variable excitation conditions and uniaxial interfacial stresses

    E-Print Network [OSTI]

    Vardi, Amichay

    The emission of polarized light from GaN/AlN self-assembled quantum dots subject to variable. In this work, GaN/AlN self-assembled QDs were grown by the Stranski-Krastanov method on a Si(111) substrate expansion coefficient mismatch between the Si substrate and GaN/AlN film containing vertically stacked QDs

  17. Observation of room temperature optical absorption in InP/GaAs type-II ultrathin quantum wells and quantum dots

    SciTech Connect (OSTI)

    Singh, S. D., E-mail: devsh@rrcat.gov.in; Porwal, S.; Mondal, Puspen; Srivastava, A. K.; Mukherjee, C.; Dixit, V. K.; Sharma, T. K.; Oak, S. M. [Raja Ramanna Centre for Advanced Technology, Indore-452013, Madhya Pradesh (India)

    2014-06-14T23:59:59.000Z

    Room temperature optical absorption process is observed in ultrathin quantum wells (QWs) and quantum dots (QDs) of InP/GaAs type-II band alignment system using surface photovoltage spectroscopy technique, where no measurable photoluminescence signal is available. Clear signature of absorption edge in the sub band gap region of GaAs barrier layer is observed for the ultrathin QWs and QDs, which red shifts with the amount of deposited InP material. Movement of photogenerated holes towards the sample surface is proposed to be the main mechanism for the generation of surface photovoltage in type-II ultrathin QWs and QDs. QDs of smaller size are found to be free from the dislocations as confirmed by the high resolution transmission electron microscopy images.

  18. Accurate determination of energy scales in few-electron double quantum dots D. Taubert,1

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    methods to determine the gate voltage to energy conversion accurately in the different regimes of dot-lead tunnel couplings and demonstrate strong variations of the conversion factors. Our concepts can easily involves a conversion of the applied gate voltages to energy differences between the electronic states

  19. Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe

    E-Print Network [OSTI]

    A. E. Nikolaenko; E. A. Chekhovich; M. N. Makhonin; I. W. Drouzas; A. B. Vankov; J. Skiba-Szymanska; M. S. Skolnick; P. Senellart; A. Lemaitre; A. I. Tartakovskii

    2009-01-15T23:59:59.000Z

    Nuclear spin polarization dynamics are measured in optically pumped individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear polarization decay times of ~ 1 minute have been found indicating inefficient nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in externally applied magnetic field. A spin diffusion coefficient two orders lower than that previously found in bulk GaAs is deduced.

  20. Evidence of significant down-conversion in a Si-based solar cell using CuInS{sub 2}/ZnS core shell quantum dots

    SciTech Connect (OSTI)

    Gardelis, Spiros, E-mail: S.Gardelis@imel.demokritos.gr; Nassiopoulou, Androula G. [NCSR Demokritos INN, Terma Patriarchou Grigoriou, Aghia Paraskevi, 15310 Athens (Greece)

    2014-05-05T23:59:59.000Z

    We report on the increase of up to 37.5% in conversion efficiency of a Si-based solar cell after deposition of light-emitting Cd-free, CuInS{sub 2}/ZnS core shell quantum dots on the active area of the cell due to the combined effect of down-conversion and the anti- reflecting property of the dots. We clearly distinguished the effect of down-conversion from anti-reflection and estimated an enhancement of up to 10.5% in the conversion efficiency due to down-conversion.

  1. Non-classical higher-order photon correlations with a quantum dot strongly coupled to a photonic-crystal nanocavity

    E-Print Network [OSTI]

    Armand Rundquist; Michal Bajcsy; Arka Majumdar; Tomas Sarmiento; Kevin Fischer; Konstantinos G. Lagoudakis; Sonia Buckley; Alexander Y. Piggott; Jelena Vuckovic

    2014-08-12T23:59:59.000Z

    We use the third- and fourth-order autocorrelation functions $g^{(3)}(\\tau_1,\\tau_2)$ and $g^{(4)}(\\tau_1,\\tau_2, \\tau_3)$ to detect the non-classical character of the light transmitted through a photonic-crystal nanocavity containing a strongly-coupled quantum dot probed with a train of coherent light pulses. We contrast the value of $g^{(3)}(0, 0)$ with the conventionally used $g^{(2)}(0)$ and demonstrate that in addition to being necessary for detecting two-photon states emitted by a low-intensity source, $g^{(3)}$ provides a more clear indication of the non-classical character of a light source. We also present preliminary data that demonstrates bunching in the fourth-order autocorrelation function $g^{(4)}(\\tau_1,\\tau_2, \\tau_3)$ as the first step toward detecting three-photon states.

  2. Influence of Gaussian white noise on the frequency-dependent first nonlinear polarizability of doped quantum dot

    SciTech Connect (OSTI)

    Ganguly, Jayanta [Department of Chemistry, Brahmankhanda Basapara High School, Basapara, Birbhum 731215, West Bengal (India); Ghosh, Manas, E-mail: pcmg77@rediffmail.com [Department of Chemistry, Physical Chemistry Section, Visva Bharati University, Santiniketan, Birbhum 731 235, West Bengal (India)

    2014-05-07T23:59:59.000Z

    We investigate the profiles of diagonal components of frequency-dependent first nonlinear (?{sub xxx} and ?{sub yyy}) optical response of repulsive impurity doped quantum dots. We have assumed a Gaussian function to represent the dopant impurity potential. This study primarily addresses the role of noise on the polarizability components. We have invoked Gaussian white noise consisting of additive and multiplicative characteristics (in Stratonovich sense). The doped system has been subjected to an oscillating electric field of given intensity, and the frequency-dependent first nonlinear polarizabilities are computed. The noise characteristics are manifested in an interesting way in the nonlinear polarizability components. In case of additive noise, the noise strength remains practically ineffective in influencing the optical responses. The situation completely changes with the replacement of additive noise by its multiplicative analog. The replacement enhances the nonlinear optical response dramatically and also causes their maximization at some typical value of noise strength that depends on oscillation frequency.

  3. What is measured in a photoluminescence experiment on Quantum dots embedded in a large Purcell factor microcavity?

    E-Print Network [OSTI]

    Bruno Gayral; Jean-Michel Gerard

    2008-08-07T23:59:59.000Z

    It is usually assumed that when performing a photoluminescence experiment on a microcavity containing an inhomogeneously broadened quantum dots ensemble, the cavity mode appears as a positive peak with a linewidth that reflects the mode quality factor Q. We show in this article that this conclusion is in general not true, and that the measured mode linewidth depends strongly on the excitation power for microcavities having large Purcell factors. We analyze theoretically this effect in the case of the micropillar cavity and we show that the same microcavity can give rise to a large variety of photoluminescence spectral signatures depending on the excitation power and collection set-up. We finally give guidelines to measure the real cavity quality factor by photoluminescence.

  4. Blinking suppression of CdTe quantum dots on epitaxial graphene and the analysis with Marcus electron transfer

    SciTech Connect (OSTI)

    Hirose, Takuya; Tamai, Naoto, E-mail: tamai@kwansei.ac.jp [Department of Chemistry, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337 (Japan); Kutsuma, Yasunori; Kurita, Atsusi; Kaneko, Tadaaki [Department of Physics, School of Science and Technology, Kwansei Gakuin University, 2-1 Gakuen, Sanda, Hyogo 669-1337 (Japan)

    2014-08-25T23:59:59.000Z

    We have prepared epitaxial graphene by a Si sublimation method from 4H-SiC. Single-particle spectroscopy of CdTe quantum dots (QDs) on epitaxial graphene covered with polyvinylpyrrolidone (PVP) or polyethylene glycol (PEG) showed the suppression of luminescence blinking and ?10 times decreased luminescence intensity as compared with those on a glass. The electronic coupling constant, H{sub 01}, between CdTe QDs and graphene was calculated to be (3.3?±?0.4)?×?10{sup 2?}cm{sup ?1} in PVP and (3.7?±?0.8)?×?10{sup 2?}cm{sup ?1} in PEG based on Marcus theory of electron transfer and Tang-Marcus model of blinking with statistical distribution.

  5. Super-dense array of Ge quantum dots grown on Si(100) by low-temperature molecular beam epitaxy

    SciTech Connect (OSTI)

    Talochkin, A. B., E-mail: tal@isp.nsc.ru; Shklyaev, A. A. [A.V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Mashanov, V. I. [A.V. Rzhanov Institute of Semiconductor Physics, Lavrentyev Avenue 13, Novosibirsk 630090 (Russian Federation)

    2014-04-14T23:59:59.000Z

    Ge layer grown on Si(100) at the low temperature of ?100?°C by molecular beam epitaxy is studied using scanning tunneling microscopy and Raman spectroscopy. It is found that crystalline and pseudomorphic to the Si substrate Ge islands are formed at the initial growth stage. The islands acquire the base size of 1.2–2.6?nm and they form arrays with the super-high density of (5–8)?×?10{sup 12}?cm{sup ?2} at 1–2?nm Ge coverages. Such a density is at least 10 times higher than that of Ge “hut” clusters grown via the Stranski-Krastanov growth mode. It is shown that areas between the crystalline Ge islands are filled with amorphous Ge, which is suggested to create potential barrier for holes localized within the islands. As a result, crystalline Ge quantum dots appear being isolated from each other.

  6. Regular and irregular dynamics of Dirac-Weyl wavepackets in a mesoscopic quantum dot at the edge of topological insulator

    E-Print Network [OSTI]

    D. V. Khomitsky; A. A. Chubanov; A. A. Konakov

    2015-01-06T23:59:59.000Z

    The dynamics of Dirac-Weyl spin-polarized wavepackets driven by periodic electric field is considered for the electrons in a mesoscopic quantum dot formed at the edge of two-dimensional HgTe/CdTe topological insulator with Dirac-Weyl massless energy spectra, where the motion of carriers is less sensitive to disorder and impurity potentials. It is found that the interplay of strongly coupled spin and charge degrees of freedom creates the regimes of both regular and irregular dynamics with certain universal properties manifested both in the clean limit and in the presence of the moderate disorder. The disorder influence is predicted to enhance the in-plane spin relaxation, leading to possibility of establishing novel types of driven evolution in nanostructures formed in the topological insulators.

  7. Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

    SciTech Connect (OSTI)

    Pham, Chuyen V.; Krueger, Michael, E-mail: michael.krueger@fmf.uni-freiburg.de, E-mail: emre.erdem@physchem.uni-freiburg.de; Eck, Michael [Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg (Germany); Department of Microsystems Engineering (IMTEK), University of Freiburg, Georges-Köhler-Allee 103, 79110 Freiburg (Germany); Weber, Stefan; Erdem, Emre, E-mail: michael.krueger@fmf.uni-freiburg.de, E-mail: emre.erdem@physchem.uni-freiburg.de [Institute of Physical Chemistry, University of Freiburg, Albertstr. 21, 79104 Freiburg (Germany)

    2014-03-31T23:59:59.000Z

    Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g?=?2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

  8. Origins of interlayer formation and misfit dislocation displacement in the vicinity of InAs/GaAs quantum dots

    SciTech Connect (OSTI)

    Huang, S.; Kim, S. J.; Pan, X. Q. [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Goldman, R. S., E-mail: rsgold@umich.edu [Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109 (United States); Department of Physics, University of Michigan, Ann Arbor, Michigan 48109 (United States)

    2014-07-21T23:59:59.000Z

    We have examined the origins of interlayer formation and misfit dislocation (MD) displacement in the vicinity of InAs/GaAs quantum dots (QDs). For QDs formed by the Stranski-Krastanov mode, regularly spaced MDs nucleate at the interface between the QD and the GaAs buffer layer. In the droplet epitaxy case, both In island formation and In-induced “nano-drilling” of the GaAs buffer layer are observed during In deposition. Upon annealing under As flux, the In islands are converted to InAs QDs, with an InGaAs interlayer at the QD/buffer interface. Meanwhile, MDs nucleate at the QD/interlayer interface.

  9. TEM Characterization of InAs/GaAs Quantum Dots Capped by a GaSb/GaAs Layer

    SciTech Connect (OSTI)

    Beltran, AM [Universidad de Cadiz, Spain; Ben, Teresa [Universidad de Cadiz, Spain; Sanchez, AM [Universidad de Cadiz, Spain; Sales Lerida, David [ORNL; Chisholm, Matthew F [ORNL; Varela del Arco, Maria [ORNL; Pennycook, Stephen J [ORNL; Galindo, Pedro [Universidad de Cadiz, Spain; Ripalda, JM [Instituto de Microelectronica de Madrid (CNM, CSIC); Molina Rubio, Sergio I [ORNL

    2008-01-01T23:59:59.000Z

    It is well known that there is intense interest in expanding the usable wavelength for electronic devices. This is one of the reasons to study new self-assembled semiconductor nanostructures. Telecommunication applications use InGaAsP/InP emitting at 1.3 and 1.55 m. Research efforts are dedicated to develop GaAs technology in order to achieve emission at the same range as InP, so GaAs could be used for optical fibre communications. Ga(As)Sb on InAs/GaAs quantum dots (QDs) is a promising nanostructure to be used in telecommunications. The introduction of antimony during or after the QDs growth is an effective solution to obtain a red shift in the emission wavelength, even at room temperature.

  10. Enhancement of the photovoltaic performance in P3HT: PbS hybrid solar cells using small size PbS quantum dots

    SciTech Connect (OSTI)

    Firdaus, Yuliar; Van der Auweraer, Mark, E-mail: mark.vanderauweraer@chem.kuleuven.be [Laboratory of Photochemistry and Spectroscopy, Division of Molecular Imaging and Photonics, Chemistry Department, KULeuven, Celestijnenlaan 200F, 2404, B-3001 Leuven (Belgium); Vandenplas, Erwin; Gehlhaar, Robert; Cheyns, David [Imec vzw, Kapeldreef 75, B-3001 Leuven (Belgium); Justo, Yolanda; Hens, Zeger [Physical Chemistry Laboratory, Ghent University, Krijgslaan 281-S3, 9000 Gent (Belgium)

    2014-09-07T23:59:59.000Z

    Different approaches of surface modification of the quantum dots (QDs), namely, solution-phase (octylamine, octanethiol) and post-deposition (acetic acid, 1,4-benzenedithiol) ligand exchange were used in the fabrication of hybrid bulk heterojunction solar cell containing poly (3-hexylthiophene) (P3HT) and small (2.4?nm) PbS QDs. We show that replacing oleic acid by shorter chain ligands improves the figures of merit of the solar cells. This can possibly be attributed to a combination of a reduced thickness of the barrier for electron transfer and an optimized phase separation. The best results were obtained for post-deposition ligand exchange by 1,4-benzenedithiol, which improves the power conversion efficiency of solar cells based on a bulk heterojunction of lead sulfide (PbS) QDs and P3HT up to two orders of magnitude over previously reported hybrid cells based on a bulk heterojunction of P3HT:PbS QDs, where the QDs are capped by acetic acid ligands. The optimal performance was obtained for solar cells with 69?wt.?% PbS QDs. Besides the ligand effects, the improvement was attributed to the formation of an energetically favorable bulk heterojunction with P3HT, when small size (2.4?nm) PbS QDs were used. Dark current density-voltage (J-V) measurements carried out on the device provided insight into the working mechanism: the comparison between the dark J-V characteristics of the bench mark system P3HT:PCBM and the P3HT:PbS blends allows us to conclude that a larger leakage current and a more efficient recombination are the major factors responsible for the larger losses in the hybrid system.

  11. Structural and orientation effects on electronic energy transfer between silicon quantum dots with dopants and with silver adsorbates

    SciTech Connect (OSTI)

    Vinson, N.; Freitag, H.; Micha, D. A., E-mail: micha@qtp.ufl.edu [Quantum Theory Project, Departments of Chemistry and Physics, University of Florida, Gainesville, Florida 32611 (United States)

    2014-06-28T23:59:59.000Z

    Starting from the atomic structure of silicon quantum dots (QDs), and utilizing ab initio electronic structure calculations within the Förster resonance energy transfer (FRET) treatment, a model has been developed to characterize electronic excitation energy transfer between QDs. Electronic energy transfer rates, K{sub EET}, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag{sub 3}, have been calculated and analyzed to extend previous work on light absorption by QDs. The effects of their size and relative orientation on energy transfer rates for each system have also been considered. Using time-dependent density functional theory and the hybrid functional HSE06, the FRET treatment was employed to model electronic energy transfer rates within the dipole-dipole interaction approximation. Calculations with adsorbed Ag show that: (a) addition of Ag increases rates up to 100 times, (b) addition of Ag{sub 3} increases rates up to 1000 times, (c) collinear alignment of permanent dipoles increases transfer rates by an order of magnitude compared to parallel orientation, and (d) smaller QD-size increases transfer due to greater electronic orbitals overlap. Calculations with dopants show that: (a) p-type and n-type dopants enhance energy transfer up to two orders of magnitude, (b) surface-doping with P and center-doping with Al show the greatest rates, and (c) K{sub EET} is largest for collinear permanent dipoles when the dopant is on the outer surface and for parallel permanent dipoles when the dopant is inside the QD.

  12. Fabrication of diamond nanowires for quantum information processing applications Birgit J.M. Hausmann a,b,

    E-Print Network [OSTI]

    Loncar, Marko

    and polycrystalline diamond. Numerical modeling was used to study coupling between a Nitrogen Vacancy (NV) color crystal diamond. The heights and diameters of the polycrystalline nanowires presented in this paper are 1Fabrication of diamond nanowires for quantum information processing applications Birgit J

  13. Fabrication of quantum point contacts by engraving GaAsAlGaAs heterostructures with a diamond tip

    E-Print Network [OSTI]

    Hohls, Frank

    by hot-filament chemical vapor deposition of polycrystalline diamond onto a prepat- terned siliconFabrication of quantum point contacts by engraving GaAsÕAlGaAs heterostructures with a diamond tip for publication 17 July 2002 We use the all-diamond tip of an atomic force microscope for the direct engraving

  14. Fabrication of planar quantum magnetic disk structure using electron beam lithography, reactive ion etching, and chemical mechanical polishing

    E-Print Network [OSTI]

    Fabrication of planar quantum magnetic disk structure using electron beam lithography, reactive ion, Department of Electrical Engineering, University of Minnesota, Minneapolis, Minnesota 55455 Received 2 June's size and location, and reactive ion etching was used to form an SiO2 template. Nickel electroplating

  15. Quasi-bound states and continuum absorption background of polar Al{sub 0.5}Ga{sub 0.5}N/GaN quantum dots

    SciTech Connect (OSTI)

    Elmaghraoui, D., E-mail: elmaghraouidonia@yahoo.fr; Triki, M. [Laboratoire de physique de la matière condensé, Faculté des sciences de Tunis, Campus universitaire 2092 El Manar (Tunisia); Jaziri, S. [Laboratoire de physique de la matière condensé, Faculté des sciences de Tunis, Campus universitaire 2092 El Manar (Tunisia); Laboratoire de Physique des Matériaux, Faculté des Sciences de Bizerte 7021 Jarzouna (Tunisia); Leroux, M.; Brault, J. [Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Rue B. Gregory, 06560 Valbonne (France)

    2014-07-07T23:59:59.000Z

    A theoretical interpretation of the photoluminescence excitation spectra of self-organized polar GaN/(Al,Ga)N quantum dots is presented. A numerical method assuming a realistic shape of the dots and including the built-in electric field effects is developed to calculate their energy structure and hence their optical absorption. The electron and hole spectra show the existence of a set of quasi-bound states that does not originate from the wetting layer and plays a crucial role in the observed absorption spectrum of the GaN/(Al,Ga)N dots. Transitions involving these quasi-bound states and wetting layer states give a sufficient explanation for the observed continuum absorption background. The properties of this absorption band, especially its extension, depend strongly on the dot's size. Our simulation provides a natural explanation of the experimental luminescence excitation spectra of ensembles of dots of different heights. Our theoretical model can be convenient for future optical studies including systems with more complicated potentials.

  16. Suppression of thermal carrier escape and efficient photo-carrier generation by two-step photon absorption in InAs quantum dot intermediate-band solar cells using a dot-in-well structure

    SciTech Connect (OSTI)

    Asahi, S.; Teranishi, H.; Kasamatsu, N.; Kada, T.; Kaizu, T.; Kita, T. [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan)

    2014-08-14T23:59:59.000Z

    We investigated the effects of an increase in the barrier height on the enhancement of the efficiency of two-step photo-excitation in InAs quantum dot (QD) solar cells with a dot-in-well structure. Thermal carrier escape of electrons pumped in QD states was drastically reduced by sandwiching InAs/GaAs QDs with a high potential barrier of Al{sub 0.3}Ga{sub 0.7}As. The thermal activation energy increased with the introduction of the barrier. The high potential barrier caused suppression of thermal carrier escape and helped realize a high electron density in the QD states. We observed efficient two-step photon absorption as a result of the high occupancy of the QD states at room temperature.

  17. Photovoltaic performance of ultra-small PbSe quantum dots

    E-Print Network [OSTI]

    Ma, Wanli

    2014-01-01T23:59:59.000Z

    Photovoltaic performance of ultra-small PbSe quantum dotssize on the photovoltaic performance of simple Schottky-typeconfinement on the photovoltaic performance, we adopted

  18. Nanotechnology for Solar-hydrogen Production via Photoelectrochemical Water-splitting: Design, Synthesis, Characterization, and Application of Nanomaterials and Quantum Dots 

    E-Print Network [OSTI]

    Alenzi, Naser D.

    2012-02-14T23:59:59.000Z

    NANOTECHNOLOGY FOR SOLAR-HYDROGEN PRODUCTION VIA PHOTOELECTROCHEMICAL WATER-SPLITTING: DESIGN, SYNTHESIS, CHARACTERIZATION, AND APPLICATION OF NANOMATERIALS AND QUANTUM DOTS A Dissertation by NASER D. ALENZI Submitted... to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2010 Major Subject: Petroleum Engineering NANOTECHNOLOGY FOR SOLAR-HYDROGEN PRODUCTION VIA...

  19. Sandia National Laboratories: Quantum Optics

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    ClimateQuantum Optics Quantum Optics videobanner Quantum Optics with a Single Semiconductor Quantum Dot Speaker: Weng Chow, EFRC Scientist Date: September 14, 2011 Event:...

  20. Three-dimensional assemblies built up by quantum dots in size-quantization regime: Band gap shifts due to size-distribution of cadmium selenide nanoparticles

    SciTech Connect (OSTI)

    Pejova, Biljana, E-mail: biljana@pmf.ukim.mk

    2013-11-15T23:59:59.000Z

    In the present study, it is predicted that the band gap energy of a three-dimensional quantum dot assembly exhibits a red shift when the dispersion of the crystal size distribution is enlarged, even at a fixed average value thereof. The effect is manifested when the size quantization regime in individual quantum dots constituting the assembly has been entered. Under the same conditions, the sub-band gap absorption tails are characterized with large Urbach energies, which could be one or two orders of magnitude larger than the value characteristic for the non-quantized case. - Graphical abstract: Band gap shifts due to size-distribution of nanoparticles in 3D assemblies built up by quantum dots in size-quantization regime. Display Omitted - Highlights: • Optical absorption of 3D QD assemblies in size-quantization regime is modeled. • Band gap energy of the QD solid depends on the size-distribution of the nanoparticles. • QD solid samples with same ?R? exhibit band gap shift depending on size distribution. • QD size distribution leads to large Urbach energies.

  1. Rapid thermal annealing of InAs/GaAs quantum dots with a low-temperature-grown InGaP cap layer

    SciTech Connect (OSTI)

    Jiang, W.H.; Thompson, D.A.; Hul'ko, O.; Robinson, B.J.; Mascher, P. [Centre for Electrophotonic Materials and Devices (CEMD), McMaster University, Hamilton, Ontario L8S 4L7 (Canada)

    2006-05-15T23:59:59.000Z

    A single layer of self-assembled InAs quantum dots was grown on a GaAs (001) substrate by gas source molecular-beam epitaxy. The quantum dots were overgrown with 65 nm GaAs, 25 nm InGaP, and a 10 nm GaAs etch-stop layer. This was either uncapped or capped with 100 nm of low-temperature (LT)-grown, lattice-matched InGaP (LT-InGaP) or with a SiO{sub 2} layer or Al{sub 2}O{sub 3} layer. Photoluminescence (PL) measurements were made on samples before and after rapid thermal annealing at 550-900 deg.C and for 15-120 s at 650 deg.C. Samples capped with LT-InGaP showed a significant blueshift of the PL peak wavelength for anneals above 575 deg.C. By comparison, for the SiO{sub 2}-capped and uncapped samples, the net blueshift only becomes significant for anneals >700 deg.C, while an Al{sub 2}O{sub 3} cap actually reduces the blueshift and suppresses the intermixing. It appears that the best conditions for spatially controlling the quantum dot intermixing occur with annealing at low temperatures (600-650 deg.C)

  2. Synthesis and enzymatic cleavage of dual-ligand quantum dots Sarah L. Sewell a

    E-Print Network [OSTI]

    cleavage by matrix metalloprotease-7 (MMP-7). The QDs were further functionalized with folic acid, a ligand functionalized with both the MMP-7 cleavable substrate and folic acid were successfully synthesized molecule, ubiquitous cancer targeting ligands. In this work, we have designed and fabricated a nanoparticle

  3. Gate-Dependent Carrier Diffusion Length in Lead Selenide Quantum Dot Field-Effect Transistors

    E-Print Network [OSTI]

    Yu, Dong

    -generation solar panels. Strongly confined QDs such as lead selenide (PbSe) also have the potential to benefit from- generation photovoltaic devices and sensitive photodetec- tors.1-3 The potential for low fabrication cost improvements are still necessary for QD solar cells to compete with commercial technologies. In particular

  4. Photocurrent spectrum study of a quantum dot single-photon detector based on resonant tunneling effect with near-infrared response

    SciTech Connect (OSTI)

    Weng, Q. C. [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China); Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241 (China); An, Z. H., E-mail: anzhenghua@fudan.edu.cn, E-mail: luwei@mail.sitp.ac.cn [State Key Laboratory of Surface Physics and Institute of Advanced Materials, Fudan University, Shanghai 200433 (China); Xiong, D. Y.; Zhu, Z. Q. [Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai 200241 (China); Zhang, B.; Chen, P. P.; Li, T. X.; Lu, W., E-mail: anzhenghua@fudan.edu.cn, E-mail: luwei@mail.sitp.ac.cn [National Laboratory for Infrared Physics, Shanghai Institute of Technical Physics, Chinese Academy of Sciences, Shanghai 200083 (China)

    2014-07-21T23:59:59.000Z

    We present the photocurrent spectrum study of a quantum dot (QD) single-photon detector using a reset technique which eliminates the QD's “memory effect.” By applying a proper reset frequency and keeping the detector in linear-response region, the detector's responses to different monochromatic light are resolved which reflects different detection efficiencies. We find the reset photocurrent tails up to 1.3??m wavelength and near-infrared (?1100?nm) single-photon sensitivity is demonstrated due to interband transition of electrons in QDs, indicating the device a promising candidate both in quantum information applications and highly sensitive imaging applications operating in relative high temperatures (>80?K).

  5. Bright three-band white light generated from CdSe/ZnSe quantum dot-assisted Sr{sub 3}SiO{sub 5}:Ce{sup 3+},Li{sup +}-based white light-emitting diode with high color rendering index

    SciTech Connect (OSTI)

    Jang, Ho Seong; Kwon, Byoung-Hwa; Jeon, Duk Young [Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-dong, Yuseong-gu, Daejeon 305-701 (Korea, Republic of); Yang, Heesun [Department of Materials Science and Engineering, Hongik University, 72-1, Sangsu-dong, Mapo-gu, Seoul 121-791 (Korea, Republic of)

    2009-10-19T23:59:59.000Z

    In this study, bright three-band white light was generated from the CdSe/ZnSe quantum dot (QD)-assisted Sr{sub 3}SiO{sub 5}:Ce{sup 3+},Li{sup +}-based white light-emitting diode (WLED). The CdSe/ZnSe core/shell structure was confirmed by energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy. The CdSe/ZnSe QDs showed high quantum efficiency (79%) and contributed to the high luminous efficiency ({eta}{sub L}) of the fabricated WLED. The WLED showed bright natural white with excellent color rendering property ({eta}{sub L}=26.8 lm/W, color temperature=6140 K, and color rendering index=85) and high stability against the increase in forward bias currents from 20 to 70 mA.

  6. Amorphous Ge quantum dots embedded in SiO{sub 2} formed by low energy ion implantation

    SciTech Connect (OSTI)

    Zhao, J. P. [Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States); Department of Physics, University of Houston, Houston, Texas 77204 (United States); Department of Chemistry, University of Houston, Houston, Texas 77204 (United States); Huang, D. X.; Jacobson, A. J. [Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States); Department of Chemistry, University of Houston, Houston, Texas 77204 (United States); Chen, Z. Y.; Makarenkov, B. [Department of Chemistry, University of Houston, Houston, Texas 77204 (United States); Chu, W. K. [Texas Center for Superconductivity, University of Houston, Houston, Texas 77204 (United States); Department of Physics, University of Houston, Houston, Texas 77204 (United States); Bahrim, B. [Department of Chemistry and Physics, Lamar University, Beaumont, Texas 77710 (United States); Rabalais, J. W. [Department of Chemistry, University of Houston, Houston, Texas 77204 (United States); Department of Chemistry and Physics, Lamar University, Beaumont, Texas 77710 (United States)

    2008-06-15T23:59:59.000Z

    Under ultrahigh vacuum conditions, extremely small Ge nanodots embedded in SiO{sub 2}, i.e., Ge-SiO{sub 2} quantum dot composites, have been formed by ion implantation of {sup 74}Ge{sup +} isotope into (0001) Z-cut quartz at a low kinetic energy of 9 keV using varying implantation temperatures. Transmission electron microscopy (TEM) images and micro-Raman scattering show that amorphous Ge nanodots are formed at all temperatures. The formation of amorphous Ge nanodots is different from reported crystalline Ge nanodot formation by high energy ion implantation followed by a necessary high temperature annealing process. At room temperature, a confined spatial distribution of the amorphous Ge nanodots can be obtained. Ge inward diffusion was found to be significantly enhanced by a synergetic effect of high implantation temperature and preferential sputtering of surface oxygen, which induced a much wider and deeper Ge nanodot distribution at elevated implantation temperature. The bimodal size distribution that is often observed in high energy implantation was not observed in the present study. Cross-sectional TEM observation and the depth profile of Ge atoms in SiO{sub 2} obtained from x-ray photoelectron spectra revealed a critical Ge concentration for observable amorphous nanodot formation. The mechanism of formation of amorphous Ge nanodots and the change in spatial distribution with implantation temperature are discussed.

  7. Impact ionization of excitons in Ge/Si structures with Ge quantum dots grown on the oxidized Si(100) surfaces

    SciTech Connect (OSTI)

    Shklyaev, A. A. [A. V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation); Shegai, O. A. [A. V. Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Nakamura, Y. [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Ichikawa, M. [Department of Applied Physics, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2014-05-28T23:59:59.000Z

    Photoconductivity (PC) of Si/Ge structures with Ge quantum dots (QDs) grown on the Si(100) surfaces covered with the ultrathin, about 0.3–0.5?nm thick, SiO{sub 2} films is studied as a function of the interband light intensity under various lateral voltages. The structures exhibit PC with steps and a step with a peak at the step edge for low- and high-temperature grown structures, respectively. These PC features are associated with the impact ionization of QD-related excitons. The PC at step edges increases by several orders of magnitude for a certain value which is governed by the balance between rates of photo-generation, recombination, and impact ionization of excitons. The electron localization deeper in Si from the Ge QD layer in conjunction with a narrow binding-energy distribution of excitons is suggested to be the main reason that provides the sharpness of PC steps. The PC appears to be very sensitive to the impact ionization and QD preparation conditions. This allows revealing the specific characteristics of QD structures, related to their electronic and structural properties.

  8. Realization of solid-state nanothermometer using Ge quantum-dot single-hole transistor in few-hole regime

    SciTech Connect (OSTI)

    Chen, I. H.; Lai, W. T.; Li, P. W., E-mail: pwli@ee.ncu.edu.tw [Department of Electrical Engineering and Center for Nano Science and Technology, National Central University, ChungLi 32001, Taiwan (China)

    2014-06-16T23:59:59.000Z

    Semiconductor Ge quantum-dot (QD) thermometry has been demonstrated based on extraordinary temperature-dependent oscillatory differential conductance (G{sub D}) characteristics of Ge-QD single-hole transistors (SHTs) in the few-hole regime. Full-voltage width-at-half-minimum, V{sub 1/2}, of G{sub D} valleys appears to be fairly linear in the charge number (n) and temperature within the QD in a relationship of eV{sub 1/2}???(1???0.11n)?×?5.15k{sub B}T, providing the primary thermometric quantity. The depth of G{sub D} valley is also proportional to charging energy (E{sub C}) and 1/T via ?G{sub D}???E{sub C}/9.18k{sub B}T, providing another thermometric quantity. This experimental demonstration suggests our Ge-QD SHT offering effective building blocks for nanothermometers over a wide temperature range with a detection temperature as high as 155?K in a spatial resolution less than 10?nm and temperature accuracy of sub-kelvin.

  9. Phonon-mediated squeezing of the cavity field off-resonantly coupled with a coherently driven quantum dot

    SciTech Connect (OSTI)

    Zhu, Jia-pei [Department of Physics, Huazhong Normal University, Wuhan 430079 (China); College of Science, Honghe University, Mengzi 661100 (China); Huang, Hui; Li, Gao-xiang, E-mail: gaox@phy.ccnu.edu.cn [Department of Physics, Huazhong Normal University, Wuhan 430079 (China)

    2014-01-21T23:59:59.000Z

    We theoretically propose a scheme for the quadrature squeezing of the cavity field via dissipative processes. The effects of the electron-phonon interaction (EPI) on the squeezing are investigated, where the cavity is off-resonantly coupled with a coherently driven quantum dot (QD) which is allowed to interact with an acoustic-phonon reservoir. Under certain conditions, the participation of the phonon induced by both the EPI and the off-resonant coupling of the cavity with the QD enables some dissipative processes to occur resonantly in the dressed-state basis of the QD. The cavity-mode photons emitted or absorbed during the phonon-mediated dissipative processes are correlated, thus leading to the squeezing of the cavity field. A squeezed vacuum reservoir for the cavity field is built up due to the EPI plus the off-resonant coupling between the cavity and the QD. The numerical results obtained with an effective polaron master equation derived using second-order perturbation theory indicate that, in low temperature limit, the degree of squeezing is maximal but the increasing temperature of the phonon reservoir could hinder the squeezing and degrade the degree of the squeezing of the cavity field. In addition, the presence of the photonic crystal could enhance the quadrature squeezing of the cavity field.

  10. Uptake, Translocation, and Transformation of Quantum Dots with Cationic versus Anionic Coatings by Populus deltoides nigra

    E-Print Network [OSTI]

    Alvarez, Pedro J.

    , and Pedro J. J. Alvarez*, Department of Civil & Environmental Engineering, Department of Chemistry of Civil & Environmental Engineering, University of Iowa, Iowa City, Iowa 52242, United States *S functionality for cellular labeling, drug delivery, solar cells, and quantum computation.1-3 Their fluorescent

  11. Impact of stress relaxation in GaAsSb cladding layers on quantum dot creation in InAs/GaAsSb structures grown on GaAs (001)

    SciTech Connect (OSTI)

    Bremner, S. P. [School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney 2052 (Australia)] [School of Photovoltaic and Renewable Energy Engineering, University of New South Wales, Sydney 2052 (Australia); Ban, K.-Y.; Faleev, N. N.; Honsberg, C. B. [School of Electrical, Computer and Energy Engineering, Ira A. Fulton Schools of Engineering, Solar Power Lab, Arizona State University, Tempe, Arizona 85287 (United States)] [School of Electrical, Computer and Energy Engineering, Ira A. Fulton Schools of Engineering, Solar Power Lab, Arizona State University, Tempe, Arizona 85287 (United States); Smith, D. J. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)] [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

    2013-09-14T23:59:59.000Z

    We describe InAs quantum dot creation in InAs/GaAsSb barrier structures grown on GaAs (001) wafers by molecular beam epitaxy. The structures consist of 20-nm-thick GaAsSb barrier layers with Sb content of 8%, 13%, 15%, 16%, and 37% enclosing 2 monolayers of self-assembled InAs quantum dots. Transmission electron microscopy and X-ray diffraction results indicate the onset of relaxation of the GaAsSb layers at around 15% Sb content with intersected 60° dislocation semi-loops, and edge segments created within the volume of the epitaxial structures. 38% relaxation of initial elastic stress is seen for 37% Sb content, accompanied by the creation of a dense net of dislocations. The degradation of In surface migration by these dislocation trenches is so severe that quantum dot formation is completely suppressed. The results highlight the importance of understanding defect formation during stress relaxation for quantum dot structures particularly those with larger numbers of InAs quantum-dot layers, such as those proposed for realizing an intermediate band material.

  12. Elemental diffusion during the droplet epitaxy growth of In(Ga)As/GaAs(001) quantum dots by metal-organic chemical vapor deposition

    SciTech Connect (OSTI)

    Chen, Z. B.; Chen, B.; Wang, Y. B.; Liao, X. Z., E-mail: xiaozhou.liao@sydney.edu.au [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Lei, W. [School of Electrical, Electronic and Computer Engineering, The University of Western Australia, Perth, WA 6009 (Australia); Tan, H. H.; Jagadish, C. [Department of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200 (Australia); Zou, J. [Materials Engineering and Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, QLD 4072 (Australia); Ringer, S. P. [School of Aerospace, Mechanical and Mechatronic Engineering, The University of Sydney, Sydney, NSW 2006 (Australia); Australian Centre for Microscopy and Microanalysis, The University of Sydney, Sydney, NSW 2006 (Australia)

    2014-01-13T23:59:59.000Z

    Droplet epitaxy is an important method to produce epitaxial semiconductor quantum dots (QDs). Droplet epitaxy of III-V QDs comprises group III elemental droplet deposition and the droplet crystallization through the introduction of group V elements. Here, we report that, in the droplet epitaxy of InAs/GaAs(001) QDs using metal-organic chemical vapor deposition, significant elemental diffusion from the substrate to In droplets occurs, resulting in the formation of In(Ga)As crystals, before As flux is provided. The supply of As flux suppresses the further elemental diffusion from the substrate and promotes surface migration, leading to large island formation with a low island density.

  13. Effects of n-type doping in InAs/GaAs quantum dot layer on current-voltage characteristic of intermediate band solar cells

    E-Print Network [OSTI]

    Gu, Yong-Xian; Ji, Hai-Ming; Xu, Peng-Fei; Yang, Tao

    2013-01-01T23:59:59.000Z

    We investigated the current-voltage characteristic of InAs/GaAs quantum dot intermediate band solar cells (QD IBSCs) with different n-type doping density in the QD layer. The n-type doping evidently increases the open circuit voltage, meanwhile decreases the short circuit current density, and leads to the conversion efficiency approaching that of the control solar cell, that is the major role of n-type doping is to suppress the effects of QDs on the current-voltage characteristic. Our model adopts practical parameters for simulation rather than those from detailed balanced method, so that the results in our simulation are not overestimated.

  14. Temperature-dependent measurement of Auger recombination in In{sub 0.40}Ga{sub 0.60}N/GaN red-emitting (??=?630?nm) quantum dots

    SciTech Connect (OSTI)

    Frost, Thomas; Banerjee, Animesh; Jahangir, Shafat; Bhattacharya, Pallab, E-mail: pkb@eecs.umich.edu [Center for Photonics and Multiscale Nanomaterials, Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)

    2014-02-24T23:59:59.000Z

    We have derived the Auger recombination coefficients, as a function of temperature, for In{sub 0.4}Ga{sub 0.6}N/GaN self-organized quantum dots from large-signal modulation measurements made on lasers in which the quantum dots form the gain media. The value of C{sub a}?=?1.3?±0.2 ×?10{sup ?31}?cm{sup 6}?s{sup ?1} at room temperature and the coefficient decreases with increase of temperature.

  15. Optimized fabrication and characterization of carbon nanotube spin valves

    SciTech Connect (OSTI)

    Samm, J.; Gramich, J.; Baumgartner, A., E-mail: andreas.baumgartner@unibas.ch; Weiss, M.; Schönenberger, C. [Institute of Physics, University of Basel, Klingelbergstrasse 82, 4056 Basel (Switzerland)

    2014-05-07T23:59:59.000Z

    We report an improved fabrication scheme for carbon based nanospintronic devices and demonstrate the necessity for a careful data analysis to investigate the fundamental physical mechanisms leading to magnetoresistance. The processing with a low-density polymer and an optimised recipe allows us to improve the electrical, magnetic, and structural quality of ferromagnetic Permalloy contacts on lateral carbon nanotube (CNT) quantum dot spin valve devices, with comparable results for thermal and sputter deposition of the material. We show that spintronic nanostructures require an extended data analysis, since the magnetization can affect all characteristic parameters of the conductance features and lead to seemingly anomalous spin transport. In addition, we report measurements on CNT quantum dot spin valves that seem not to be compatible with the orthodox theories for spin transport in such structures.

  16. The effect of photo-generated carriers on the spectral diffusion of a quantum dot coupled to a photonic crystal cavity

    E-Print Network [OSTI]

    Arka Majumdar; Erik D. Kim; Jelena Vuckovic

    2011-07-24T23:59:59.000Z

    We experimentally observe the effect of photo-generated carriers on the spectral diffusion of a quantum dot (QD) coupled to a photonic crystal (PC) cavity. In this system, spectral diffusion arises in part from charge fluctuations on the etched surfaces of the PC. We find that these fluctuations may be suppressed by photo-generated carriers, leading to a reduction of the measured QD linewidth by a factor of ~2 compared to the case where the photo-generated carriers are not present. This result demonstrates a possible means of countering the effects of spectral diffusion in QD-PC cavity systems and thus may be useful for quantum information applications where narrow QD linewidths are desired.

  17. Size dependent optical properties of Si quantum dots in Si-rich nitride/Si{sub 3}N{sub 4} superlattice synthesized by magnetron sputtering

    SciTech Connect (OSTI)

    So, Yong-Heng; Huang, Shujuan; Conibeer, Gavin; Green, Martin A. [ARC Photovoltaics Centre of Excellence, University of New South Wales, Sydney, New South Wales 2052 (Australia); Gentle, Angus [Physics and Advanced Materials, University of Technology Sydney, P. O. Box 123, Broadway, New South Wales 2007 (Australia)

    2011-03-15T23:59:59.000Z

    A spectroscopic ellipsometry compatible approach is reported for the optical study of Si quantum dots (QDs) in Si-rich nitride/silicon nitride (SRN/Si{sub 3}N{sub 4}) superlattice, which based on Tauc-Lorentz model and Bruggeman effective medium approximation. It is shown that the optical constants and dielectric functions of Si QDs are strongly size dependent. The suppressed imaginary dielectric function of Si QDs exhibits a single broad peak analogous to amorphous Si, which centered between the transition energies E{sub 1} and E{sub 2} of bulk crystalline Si and blue shifted toward E{sub 2} as the QD size reduced. A bandgap expansion observed by the TL model when the size of Si QD reduced is in good agreement with the PL measurement. The bandgap expansion with the reduction of Si QD size is well supported by the first-principles calculations based on quantum confinement.

  18. Tunnel-injection quantum dot deep-ultraviolet light-emitting diodes with polarization-induced doping in III-nitride heterostructures

    SciTech Connect (OSTI)

    Verma, Jai, E-mail: jverma@nd.edu; Islam, S. M.; Protasenko, Vladimir; Kumar Kandaswamy, Prem; Xing, Huili; Jena, Debdeep [Department of Electrical Engineering, University of Notre Dame, Notre Dame, Indiana 46556 (United States)

    2014-01-13T23:59:59.000Z

    Efficient semiconductor optical emitters in the deep-ultraviolet spectral window are encountering some of the most deep rooted problems of semiconductor physics. In III-Nitride heterostructures, obtaining short-wavelength photon emission requires the use of wide bandgap high Al composition AlGaN active regions. High conductivity electron (n-) and hole (p-) injection layers of even higher bandgaps are necessary for electrical carrier injection. This approach requires the activation of very deep dopants in very wide bandgap semiconductors, which is a difficult task. In this work, an approach is proposed and experimentally demonstrated to counter the challenges. The active region of the heterostructure light emitting diode uses ultrasmall epitaxially grown GaN quantum dots. Remarkably, the optical emission energy from GaN is pushed from 365?nm (3.4?eV, the bulk bandgap) to below 240?nm (>5.2?eV) because of extreme quantum confinement in the dots. This is possible because of the peculiar bandstructure and band alignments in the GaN/AlN system. This active region design crucially enables two further innovations for efficient carrier injection: Tunnel injection of carriers and polarization-induced p-type doping. The combination of these three advances results in major boosts in electroluminescence in deep-ultraviolet light emitting diodes and lays the groundwork for electrically pumped short-wavelength lasers.

  19. Transport through open quantum dots: Making semiclassics quantitative Iva B#ezinov, 1, e i z, e an o e , 1 i o a e , an oa i B e 1

    E-Print Network [OSTI]

    Rotter, Stefan

    Transport through open quantum dots: Making semiclassics quantitative Iva B#ezinová, 1, e i z, e an o e , 1 i o a e , an oa i B e 1 1 Institute for Theoretical Physics, Vienna University of Technology JARA­FIT and II. Institute of Physics, RWTH Aachen, 52074 Aachen, Germany, EU # e eive o e i e a 1 # e

  20. Passive correction of quantum logical errors in a driven, dissipative system: a blueprint for an analog quantum code fabric

    E-Print Network [OSTI]

    Eliot Kapit; John T. Chalker; Steven H. Simon

    2014-08-05T23:59:59.000Z

    A physical realization of self correcting quantum code would be profoundly useful for constructing a quantum computer. In this theoretical work, we provide a partial solution to major challenges preventing self correcting quantum code from being engineered in realistic devices. We consider a variant of Kitaev's toric code coupled to propagating bosons, which induce a long-ranged interaction between anyonic defects. By coupling the primary quantum system to an engineered dissipation source through resonant energy transfer, we demonstrate a "rate barrier" which leads to a potentially enormous increase in the system's quantum state lifetime through purely passive quantum error correction, even when coupled to an infinite temperature bath. While our mechanism is not scalable to infinitely large systems, the maximum effective size can be very large, and it is fully compatible with active error correction schemes. Our model uses only on-site and nearest-neighbor interactions, and could be implemented in superconducting qubits. We sketch one such implementation at the end of this work.

  1. Stark effect in ensembles of polar (0001) Al{sub 0.5}Ga{sub 0.5}N/GaN quantum dots and comparison with semipolar (11?22) ones

    SciTech Connect (OSTI)

    Leroux, M.; Brault, J.; Kahouli, A.; Damilano, B.; Mierry, P. de; Korytov, M. [Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications, CNRS, Rue Bernard Grégory, 06560 Valbonne (France); Maghraoui, D. [Laboratoire de Physique de la Matière Condensée, Faculté des Sciences de Tunis, 2092 El Manar (Tunisia); Kim, Je-Hyung; Cho, Yong-Hoon [Department of Physics and KI for the NanoCentury, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 305-701 (Korea, Republic of)

    2014-07-21T23:59:59.000Z

    This work presents a continuous-wave photoluminescence study of Al{sub 0.5}Ga{sub 0.5}N/GaN quantum dots grown by ammonia-assisted molecular beam epitaxy on sapphire, either on the wurtzite polar (0001) or the semipolar (11?22) plane. Due to interface polarization discontinuities, the polar dots are strongly red-shifted by the Stark effect and emit in the visible range. Carrier injection screening of the polarization charges has been studied. A model relying on average dot heights and dot height variances, as measured by transmission electron microscopy, is proposed. It can account for the injection dependent luminescence energies and efficiencies. The electric field discontinuity deduced from the fittings is in good agreement with theoretical expectations for our barrier composition. On the contrary, semipolar quantum dot ensembles always emit above the gap of GaN strained to Al{sub 0.5}Ga{sub 0.5}N. Their luminescence linewidth is significantly lower than that of polar ones, and their energy does not shift with injection. Our study then confirms the expected strong decrease of the Stark effect for (11?22) grown (Al,Ga)N/GaN heterostructures.

  2. A level set simulation for ordering of quantum dots via cleaved-edge X. B. Niu,1,2

    E-Print Network [OSTI]

    Ratsch, Christian

    applications such as next generation optoelectronic devices.1 For optimal performance of arrays of QDs it is ideal if the size distribution of the dots is rather uniform. Moreover, the exact properties of QDs can energy Etrans is sketched in Fig. 2. Within the method, island boundaries are described by a level set

  3. Determination of energy scales in few-electron double quantum dots D. Taubert, D. Schuh, W. Wegscheider, and S. Ludwig

    E-Print Network [OSTI]

    Ludwig-Maximilians-Universität, München

    gate volt- ages to energy differences between the electronic states. The conversion factors devices. We have developed methods to determine the gate voltage to energy conversion accurately in the different regimes of dot-lead tunnel couplings and demonstrate strong variations of the conversion factors

  4. PHYSICAL REVIEW E 85, 031117 (2012) Stochastically driven single-level quantum dot: A nanoscale finite-time thermodynamic

    E-Print Network [OSTI]

    Lindenberg, Katja

    2012-01-01T23:59:59.000Z

    as a nanoscale finite-time thermodynamic machine. The dot is driven by an external stochastic force that switches that extracts heat from the cold reservoir via the work input of the stochastic driving. The efficiency coupling conditions, familiar features are recovered in appropriate limits: Carnot efficiency

  5. Hybrid molecular assemblies composed of hydrogenase enzymes and quantum dots helps to pave the way for the

    E-Print Network [OSTI]

    % wastepaper, including 10% post consumer waste. Lighting Up Enzymes for Solar Hydrogen Production NREL. Scientists at the National Renewable Energy Laboratory (NREL) have combined quan- tum dots, which selectivity and fast turnover of hydrogenase enzymes to achieve light-driven hydrogen (H2) production

  6. Quantum Dots: Theory

    E-Print Network [OSTI]

    Vukmirovic, Nenad

    2010-01-01T23:59:59.000Z

    conventional conjugate gradient method [44] which is oftensolved using the conjugate gradient method. It turns outsuch as the conjugate gradient method. The atomic structure

  7. Caged Quantum Dots

    SciTech Connect (OSTI)

    Cohen, Bruce

    2008-01-01T23:59:59.000Z

    Berkeley Lab scientists have developed a nanosized crystal that lights up on command, a feat that could allow researchers to more easily observe individual proteins inside cells. http://newscenter.lbl.gov/feature-stories/2008/11/18/cagedquantumdots/

  8. Step-by-step capping and strain state of GaN/AlN quantum dots studied by grazing-incidence diffraction anomalous fine structure

    SciTech Connect (OSTI)

    Coraux, J.; Favre-Nicolin, V.; Renevier, H. [Commissariat l'Energie Atomique, Departement de Recherche Fondamentale sur la Matiere Condensee, SP2M/NRS, 17 rue des martyrs, 38054 Grenoble Cedex 9 (France); Universite Joseph Fourier, BP 53, 38041, Grenoble Cedex 9 (France); Proietti, M. G. [Departamento de Fisica de la Materia Condensada, Instituto de Ciencia de Materiales de Aragon, CSIC-Universidad de Zaragoza, c. Pedro Cerbuna 12, 50009 Zaragoza (Spain); Daudin, B. [Commissariat l'Energie Atomique, Departement de Recherche Fondamentale sur la Matiere Condensee, SP2M/NRS, 17 rue des martyrs, 38054 Grenoble Cedex 9 (France)

    2006-05-15T23:59:59.000Z

    The investigation of small-size embedded nanostructures, by a combination of complementary anomalous diffraction techniques, is reported. GaN quantum dots (QD's), grown by molecular beam epitaxy in a modified Stranski-Krastanow mode, are studied in terms of strain and local environment, as a function of the AlN cap layer thickness, by means of grazing-incidence anomalous diffraction. That is, the x-ray photon energy is tuned across the Ga absorption K edge which makes diffraction chemically selective. Measurement of hkl scans, close to the AlN (3030) Bragg reflection, at several energies across the Ga K edge, allows the extraction of the Ga partial structure factor, from which the in-plane strain of GaN QD's is deduced. From the fixed-Q energy-dependent diffracted intensity spectra, measured for diffraction-selected isostrain regions corresponding to the average in-plane strain state of the QD's, quantitative information regarding the composition and out-of-plane strain has been obtained. We recover the in-plane and out-of-plane strains in the dots. The comparison to the biaxial elastic strain in a pseudomorphic layer indicates a tendency to an overstrained regime.

  9. anisn format dot: Topics by E-print Network

    Broader source: All U.S. Department of Energy (DOE) Office Webpages (Extended Search)

    Quantum Dot Arrays and Applications of Multiple Exciton Generation to Third-Generation Photovoltaic Solar Cells Biology and Medicine Websites Summary: to Third-Generation...

  10. Effects of capping on GaN quantum dots deposited on Al{sub 0.5}Ga{sub 0.5}N by molecular beam epitaxy

    SciTech Connect (OSTI)

    Korytov, M. [CRHEA-CNRS, rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France) and University of Nice Sophia-Antipolis, Parc Valrose, 06103 Nice (France); Benaissa, M. [CNRST, angle Allal-Fassi/FAR, Madinat al-irfane, 10000 Rabat (Morocco); Brault, J.; Vennegues, P. [CRHEA-CNRS, rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne (France); Huault, T. [CRHEA-CNRS, rue Bernard Gregory, Sophia Antipolis, 06560 Valbonne, France and RIBER S.A., 31 rue Casimir Perier, BP 70083, 95873 Bezons Cedex (France); Neisius, T. [CP2M, Faculte Saint Jerome, 13397 Marseille Cedex 20 (France)

    2009-04-06T23:59:59.000Z

    The impact of the capping process on the structural and morphological properties of GaN quantum dots (QDs) grown on fully relaxed Al{sub 0.5}Ga{sub 0.5}N templates was studied by transmission electron microscopy. A morphological transition between the surface QDs, which have a pyramidal shape, and the buried ones, which have a truncated pyramid shape, is evidenced. This shape evolution is accompanied by a volume change: buried QDs are bigger than surface ones. Furthermore a phase separation into Al{sub 0.5}Ga{sub 0.5}N barriers was observed in the close vicinity of buried QDs. As a result, the buried QDs were found to be connected with the nearest neighbors by thin Ga-rich zones, whereas Al-rich zones are situated above the QDs.

  11. Chemical bonding and defect states of LPCVD grown silicon-rich Si{sub 3}N{sub 4} for quantum dot applications

    SciTech Connect (OSTI)

    Mohammed, Shakil, E-mail: smohammed@utdallas.edu; Hinkle, Christopher L., E-mail: chris.hinkle@utdallas.edu [Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080 (United States); Nimmo, Michael T.; Malko, Anton V. [Department of Physics, The University of Texas at Dallas, Richardson, Texas 75080 (United States)

    2014-03-15T23:59:59.000Z

    Si-rich Si{sub 3}N{sub 4} (SRN) thin films were investigated to understand the various defect states present within the SRN that can lead to reduced performance in quantum dot based devices made of these materials. The SRN films, deposited by low pressure chemical vapor deposition followed by furnace anneals over a range of temperatures, were determined to be comprised of two distinct phase separated SRN regions with different compositions (precipitates within a host matrix). Photoluminescence (PL) spectra showed multiple peaks convoluted together within the visible and near-visible range. Depending on deposition and annealing conditions, the films displayed changes in PL peak intensities which were correlated with chemical bonding utilizing x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, spectroscopic ellipsometry, and capacitance–voltage measurements. It is found that the PL originates from defect-state to defect-state and band edge to defect-state electronic transitions.

  12. Small-signal modulation and differential gain of red-emitting (??=?630?nm) InGaN/GaN quantum dot lasers

    SciTech Connect (OSTI)

    Frost, Thomas; Banerjee, Animesh; Bhattacharya, Pallab, E-mail: pkb@eecs.umich.edu [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)] [Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109-2122 (United States)

    2013-11-18T23:59:59.000Z

    We report small-signal modulation bandwidth and differential gain measurements of a ridge waveguide In{sub 0.4}Ga{sub 0.6}N/GaN quantum dot laser grown by molecular beam epitaxy. The laser peak emission is at ??=?630?nm. The ?3?dB bandwidth of an 800??m long device was measured to be 2.4?GHz at 250?mA under pulsed biasing, demonstrating the possibility of high-speed operation of these devices. The differential gain was measured to be 5.3?×?10{sup ?17}?cm{sup 2}, and a gain compression factor of 2.87?×?10{sup ?17}?cm{sup 3} is also derived from the small-signal modulation response.

  13. Enhanced photoluminescence due to two-photon enhanced three-photon absorption in Mn{sup 2+}-doped ZnS quantum dots

    SciTech Connect (OSTI)

    Subha, Radhu [Department of Physics, Indian Institute of Technology, Madras, Chennai, 600036, India and Department of Physics, National University of Singapore (NUS), 2 Science Drive 3, Singapore, 117542 (Singapore); Nalla, Venkatram; Ji, Wei, E-mail: phyjiwei@nus.edu.sg [Department of Physics, National University of Singapore (NUS), 2 Science Drive 3, Singapore, 117542 (Singapore); Feng, Xiaobo [School of Physics and Electronic Information Technology, Yunnan Normal University (China); Vijayan, C. [Department of Physics, Indian Institute of Technology, Madras, Chennai, 600036 (India)

    2014-10-15T23:59:59.000Z

    In this work, we have investigated the multi-photon absorption induced photoluminescence in Mn{sup 2+}-doped ZnS quantum dots in the wavelength range 860 – 1050 nm (Near-Infrared Window I). The observed three-photon action cross-section has been compared with the theoretical prediction under four band approximation. An enhancement of four to five orders has been observed in the range from 970 to 1050 nm compared to the theoretical value, which is attributed to two-photon enhanced three-photon absorption. Transient lifetime measurements reveal a lifetime of 0.35 ± 0.3 ms, which is four to five orders higher than other conventional fluorescent probes.

  14. Mortalin antibody-conjugated quantum dot transfer from human mesenchymal stromal cells to breast cancer cells requires cell–cell interaction

    SciTech Connect (OSTI)

    Pietilä, Mika [National Institute of Advanced industrial Sciences and Technology, Tsukuba, Ibaraki 305 8562 (Japan); Lehenkari, Petri [Institute of Biomedicine, Department of Anatomy and Cell Biology, University of Oulu, Aapistie 7, P.O. Box 5000, FIN-90014 (Finland); Institute of Clinical Medicine, Division of Surgery, University of Oulu and Clinical Research Centre, Department of Surgery and Intensive Care, Oulu University Hospital, Aapistie 5a, P.O. Box 5000, FIN-90014 (Finland); Kuvaja, Paula [Institute of Biomedicine, Department of Anatomy and Cell Biology, University of Oulu, Aapistie 7, P.O. Box 5000, FIN-90014 (Finland); Department of Pathology, Oulu University Hospital, P.O. Box 50, FIN-90029 OYS, Oulu (Finland); Kaakinen, Mika [Biocenter Oulu, University of Oulu, P.O. Box 5000, FI-90014 (Finland); Kaul, Sunil C.; Wadhwa, Renu [National Institute of Advanced industrial Sciences and Technology, Tsukuba, Ibaraki 305 8562 (Japan); Uemura, Toshimasa, E-mail: t.uemura@aist.go.jp [National Institute of Advanced industrial Sciences and Technology, Tsukuba, Ibaraki 305 8562 (Japan)

    2013-11-01T23:59:59.000Z

    The role of tumor stroma in regulation of breast cancer growth has been widely studied. However, the details on the type of heterocellular cross-talk between stromal and breast cancer cells (BCCs) are still poorly known. In the present study, in order to investigate the intercellular communication between human mesenchymal stromal cells (hMSCs) and breast cancer cells (BCCs, MDA-MB-231), we recruited cell-internalizing quantum dots (i-QD) generated by conjugation of cell-internalizing anti-mortalin antibody and quantum dots (QD). Co-culture of illuminated and color-coded hMSCs (QD655) and BCCs (QD585) revealed the intercellular transfer of QD655 signal from hMSCs to BCCs. The amount of QD double positive BCCs increased gradually within 48 h of co-culture. We found prominent intercellular transfer of QD655 in hanging drop co-culture system and it was non-existent when hMSCs and BBCs cells were co-cultured in trans-well system lacking imminent cell–cell contact. Fluorescent and electron microscope analyses also supported that the direct cell-to-cell interactions may be required for the intercellular transfer of QD655 from hMSCs to BCCs. To the best of our knowledge, the study provides a first demonstration of transcellular crosstalk between stromal cells and BCCs that involve direct contact and may also include a transfer of mortalin, an anti-apoptotic and growth-promoting factor enriched in cancer cells.

  15. Fabrication and testing of nano-optical structures for advanced photonics and quantum information processing applications 

    E-Print Network [OSTI]

    Khan, Mughees Mahmood

    2009-05-15T23:59:59.000Z

    -based metal nanostructures offer the promise of scalable devices. This is because the small optical mode volumes of such structures give the large atom-photon coupling needed to interface solid-state quantum bits (qubits) to photons. The main focus...

  16. High efficiency single quantum well graded-index separate-confinement heterostructure lasers fabricated with MeV oxygen ion implantation

    SciTech Connect (OSTI)

    Xiong, F.; Tombrello, T.A.; Wang, H.; Chen, T.R.; Chen, H.Z.; Morkoc, H.; Yariv, A.

    1989-02-20T23:59:59.000Z

    Single quantum well AlGaAs/GaAs graded-index separate-confinement heterostructure lasers have been fabricated using MeV oxygen ion implantation plus optimized subsequent thermal annealing. A high differential quantum efficiency of 85% has been obtained in a 360-..mu..m-long and 10-..mu..m-wide stripe geometry device. The results have also demonstrated that excellent electrical isolation (breakdown voltage of over 30 V) and low threshold currents (22 mA) can be obtained with MeV oxygen ion isolation. It is suggested that oxygen ion implantation induced selective carrier compensation and compositional disordering in the quantum well region as well as radiation-induced lattice disordering in Al/sub x/Ga/sub 1-//sub x/As/GaAs may be mostly responsible for the buried layer modification in this fabrication process.

  17. Conversion of above- and below-bandgap photons via InAs quantum dot media embedded into GaAs solar cell

    SciTech Connect (OSTI)

    Sablon, K.; Little, J. [U.S. Army Research Laboratory, Adelphi, Maryland 20783 (United States); Vagidov, N. [Optoelectronic Nanodevices LLC, Amherst, New York 14226 (United States); Li, Y.; Mitin, V.; Sergeev, A. [EE Department, University at Buffalo—SUNY, Buffalo, New York 14260 (United States)

    2014-06-23T23:59:59.000Z

    Quantum dots (QDs) provide photovoltaic conversion of below-bandgap photons due to multistep electron transitions. QDs also increase conversion efficiency of the above-bandgap photons due to extraction of electrons from QDs via Coulomb interaction with hot electrons excited by high-energy photons. Nanoscale potential profile (potential barriers) and nanoscale band engineering (AlGaAs atomically thin barriers) allow for suppression of photoelectron capture to QDs. To study these kinetic effects and to distinguish them from the absorption enhancement due to light scattering on QDs, we investigate long, 3-?m base GaAs devices with various InAs QD media with 20 and 40 QD layers. Quantum efficiency measurements show that, at least at low doping, the multistep processes in QD media are strongly affected by the wetting layer (WL). The QD media with WLs provide substantial conversion of below-bandgap photons and for devices with 40 QD layers the short circuit current reaches 29.2?mA/cm{sup 2}. The QD media with band-engineered AlGaAs barriers and reduced wetting layers (RWL) enhance conversion of high-energy photons and decrease the relaxation (thermal) losses.

  18. Low-frequency self-pulsing in single-section quantum-dot laser diodes and its relation to optothermal pulsations

    SciTech Connect (OSTI)

    Tierno, A. [Universite de Nice Sophia Antipolis, Institut Non-Lineaire de Nice, UMR 6618, F-06560 Valbonne (France); Radwell, N. [SUPA and the School of Physics and Astronomy University of Glasgow (United Kingdom); Ackemann, T. [SUPA and the Department of Physics, University of Strathclyde, Glasgow G4 0NG (United Kingdom)

    2011-10-15T23:59:59.000Z

    Self-sustained pulsations in the output of an InAs quantum dot laser diode in the MHz range are reported. The characteristics (shape, range, and frequency) are presented for the free-running laser and when optical feedback in the Littrow configuration is applied. Bistability in the light-current characteristics is observed for operating wavelengths smaller than the gain peak, but it is not present for wavelengths above the gain peak and for the free-running laser, except at elevated temperatures. The temporal evolution of the envelopes of the optical spectra is very different for operation below, around, and above the gain peak, which might be related to a change of phase-amplitude coupling across the gain maximum, in agreement with the expectation for a two-level system. The time scale and the bifurcation scenario, supported by an initial blueshift of the emission wavelength of each longitudinal mode in time-resolved optical spectra, suggests that these are optothermal pulsations similar to those reported in quantum well amplifiers [Phys. Rev. E 68, 036209 (2003)]. The mechanism of pulsation seems to be a destabilization of bistable states (due to saturable absorption in the beam wings) by a slow thermal change in the waveguiding properties.

  19. Optically pumped quantum-dot Cd(Zn)Se/ZnSe laser and microchip converter for yellow-green spectral region

    SciTech Connect (OSTI)

    Lutsenko, E V; Voinilovich, A G; Rzheutskii, N V; Pavlovskii, V N; Yablonskii, G P; Sorokin, S V; Gronin, S V; Sedova, I V; Kop'ev, Petr S; Ivanov, Sergei V; Alanzi, M; Hamidalddin, A; Alyamani, A

    2013-05-31T23:59:59.000Z

    The room temperature laser generation in the yellow-green ({lambda} = 558.5-566.7 nm) spectral range has been demonstrated under optical pumping by a pulsed nitrogen laser of Cd(Zn)Se/ZnSe quantum dot heterostructures. The maximum achieved laser wavelength was as high as {lambda} = 566.7 nm at a laser cavity length of 945 {mu}m. High values of both the output pulsed power (up to 50 W) and the external differential quantum efficiency ({approx}60%) were obtained at a cavity length of 435 {mu}m. Both a high quality of the laser heterostructure and a low lasing threshold ({approx}2 kW cm{sup -2}) make it possible to use a pulsed InGaN laser diode as a pump source. A laser microchip converter based on this heterostructure has demonstrated a maximum output pulse power of {approx}90 mW at {lambda} = 560 nm. The microchip converter was placed in a standard TO-18 (5.6 mm in diameter) laser diode package. (semiconductor lasers. physics and technology)

  20. IEEE JOURNAL OF SELECTED TOPICS IN QUANTUM ELECTRONICS, VOL. 15, NO. 3, MAY/JUNE 2009 819 Quantum Well and Dot Self-Aligned Stripe

    E-Print Network [OSTI]

    Well and Dot Self-Aligned Stripe Lasers Utilizing an InGaP Optoelectronic Confinement Layer Kristian M-aligned lasers based upon a single over- growth. A lattice-matched n-doped InGaP layer is utilized for both utilizing a lattice-matched n-doped InGaP current blocking layer that also provides optical confinement via