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Title: Spectroscopy of Single Free Standing Quantum Wells

Abstract

We investigated the interaction of quantum confined exciton states GaAs quantum wells with native surface states. Single molecule photoluminescence (PL) spectroscopy, developed by T. Huser at LLNL was used to probe the unique bare quantum wells in the free standing quantum well structure. The latter was developed by the M. D. Williams at Clark Atlanta University. The goals of the project during this budget cycle were to procure samples containing GaAs free standing QWs, identify suitable regions for PL analysis at Lawrence Livermore, analyze the structures at room temperature and at liquid nitrogen temperatures. The specific regions of interest on the sample structures were identified by scanning electron microscopy at Clark Atlanta prior to transport to LLNL. Previous attempts at other facilities using NSOM, cathodoluminescence, and conventional PL showed little luminescence activity at room temperature from the 200 {angstrom} thick wells. This suggested either excess recombination due to surface states in the quantum well region or insufficient absorption length for photoluminescence. The literature suggested that the effect of the defects could be eliminated by reducing the sample temperature below their associated activation energies. In our previous subcontract work with LLNL, a significant amount of effort was expended to modify themore » apparatus to allow low temperature measurements. The modifications were not successful and we concluded that in order to do the measurements at low temperature we would need to purchase a commercial optical cryostat to get reliable results. Ms. Rochelle Bryant worked during the summer as an intern at LLNL on the project under the supervision of C. Hollars and in collaboration with T. Huser and found that PL emission could be obtained at room temperature. This was a surprising result as the literature and our experience shows that there is no PL emission from GaAs at room temperature. We speculate that this is due to the small interaction region excited by the laser source. We proceeded with the project using this new found room temperature capability and have analyzed the effect of various chemical species on the PL emission from the GaAs QWs. We were able to observe some significant intensity modifications of the PL spectra with chemical adsorbants. This progress holds promise for the development of this structure as a chemical or biological sensor.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
883615
Report Number(s):
UCRL-TR-219998
TRN: US200615%%180
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Technical Report
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ABSORPTION; CATHODOLUMINESCENCE; CRYOSTATS; DEFECTS; EXCITONS; LASERS; LUMINESCENCE; MODIFICATIONS; NITROGEN; PHOTOLUMINESCENCE; PROBES; QUANTUM WELLS; RECOMBINATION; SCANNING ELECTRON MICROSCOPY; SPECTRA; SPECTROSCOPY

Citation Formats

Williams, M D, Hollars, C W, Huser, T, Jallow, N, Cochran, A, and Bryant, R. Spectroscopy of Single Free Standing Quantum Wells. United States: N. p., 2006. Web. doi:10.2172/883615.
Williams, M D, Hollars, C W, Huser, T, Jallow, N, Cochran, A, & Bryant, R. Spectroscopy of Single Free Standing Quantum Wells. United States. doi:10.2172/883615.
Williams, M D, Hollars, C W, Huser, T, Jallow, N, Cochran, A, and Bryant, R. Tue . "Spectroscopy of Single Free Standing Quantum Wells". United States. doi:10.2172/883615. https://www.osti.gov/servlets/purl/883615.
@article{osti_883615,
title = {Spectroscopy of Single Free Standing Quantum Wells},
author = {Williams, M D and Hollars, C W and Huser, T and Jallow, N and Cochran, A and Bryant, R},
abstractNote = {We investigated the interaction of quantum confined exciton states GaAs quantum wells with native surface states. Single molecule photoluminescence (PL) spectroscopy, developed by T. Huser at LLNL was used to probe the unique bare quantum wells in the free standing quantum well structure. The latter was developed by the M. D. Williams at Clark Atlanta University. The goals of the project during this budget cycle were to procure samples containing GaAs free standing QWs, identify suitable regions for PL analysis at Lawrence Livermore, analyze the structures at room temperature and at liquid nitrogen temperatures. The specific regions of interest on the sample structures were identified by scanning electron microscopy at Clark Atlanta prior to transport to LLNL. Previous attempts at other facilities using NSOM, cathodoluminescence, and conventional PL showed little luminescence activity at room temperature from the 200 {angstrom} thick wells. This suggested either excess recombination due to surface states in the quantum well region or insufficient absorption length for photoluminescence. The literature suggested that the effect of the defects could be eliminated by reducing the sample temperature below their associated activation energies. In our previous subcontract work with LLNL, a significant amount of effort was expended to modify the apparatus to allow low temperature measurements. The modifications were not successful and we concluded that in order to do the measurements at low temperature we would need to purchase a commercial optical cryostat to get reliable results. Ms. Rochelle Bryant worked during the summer as an intern at LLNL on the project under the supervision of C. Hollars and in collaboration with T. Huser and found that PL emission could be obtained at room temperature. This was a surprising result as the literature and our experience shows that there is no PL emission from GaAs at room temperature. We speculate that this is due to the small interaction region excited by the laser source. We proceeded with the project using this new found room temperature capability and have analyzed the effect of various chemical species on the PL emission from the GaAs QWs. We were able to observe some significant intensity modifications of the PL spectra with chemical adsorbants. This progress holds promise for the development of this structure as a chemical or biological sensor.},
doi = {10.2172/883615},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Mar 14 00:00:00 EST 2006},
month = {Tue Mar 14 00:00:00 EST 2006}
}

Technical Report:

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  • Recent advances in microfabrication techniques in conjunction with the precise growth of layers of single crystalline materials by epitaxial growth techniques allow the creation of new electro-optic microstructures. We have selectively etched compositionally modulated 111-v heterostructures to produce quantum wells (QW's) which are confined on both sides by air or vacuum. The material is patterned so to have the QW's suspended horizontally between vertical support posts. This structure is ideal for probing the local properties of solids, e.g., the interaction of quantum confined states with surface or interface states.
  • This final report describes the activities undertaken under grant "Optical Two-Dimensional Spectroscopy of Disordered Semiconductor Quantum Wells and Quantum Dots". The goal of this program was to implement optical 2-dimensional Fourier transform spectroscopy and apply it to electronic excitations, including excitons, in semiconductors. Specifically of interest are quantum wells that exhibit disorder due to well width fluctuations and quantum dots. In both cases, 2-D spectroscopy will provide information regarding coupling among excitonic localization sites.
  • A new type of optical dipole transition in GaAs quantum wells has been observed. The dipole occurs between two envelope states of the conduction band electron wavefunction, and is called a quantum well envelope state transition (QWEST). The QWEST is observed by infrared absorption in three different samples with quantum well thicknesses 65, 82, and 92 A and resonant energies of 152, 121, and 108 MeV, respectively. The oscillator strength is found to have values of over 12, in good agreement with prediction. The linewidths are seen as narrow as 10 MeV at room temperature and 7 MeV at lowmore » temperature, thus proving a narrow line resonance can indeed occur between transitions of free electrons. Techniques for the proper growth of these quantum well samples to enable observation of the QWEST have also been found using (AlGa)As compounds. This QWEST is considered to be an ideal material for an all optical digital computer. The QWEST can be made frequency matched to the inexpensive Carbon Dioxide laser with an infrared wavelength of 10 microns. The nonlinearity and fast relaxation time of the QWEST indicate a logic element with a subpicosecond switch time can be built in the near future, with a power level which will eventually be limited only by the noise from a lack of quanta to above approximately 10 microwatts. 64 refs., 35 figs., 6 tabs.« less
  • Photoluminescence (PL) was measured in a CdTe/Cd{sub 0.76}Mn{sub 0. 24}Te single quantum well structure under hydrostatic pressure up to 2.68 GPa and magnetic fields up to 30 T at 4.2 K. Pressure coefficients of exciton energies were found to be well width dependent. Magneto-PL experiments revealed negative pressure dependence of N{sub 0}({alpha}-{beta}) in barriers and saturation of T{sub 0} by the pressure.
  • Bandgap energy renormalization due to many body effects has been studied in a series of n-type 8-nm-wide GaAs/AlGaAs single quantum wells using magnetoluminescence spectroscopy at 1.4K. The 2D-carrier densities varied between 1 and 12 {times} 10{sup 11}/sq cm. At the maximum 2D-carrier density, the bandgap energy reduction compared to an undoped specimen was found to be about 34 meV.