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Title: In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001)

Abstract

A monitoring technique for molecular beam epitaxial growth of InAs/GaAs(001) nanoislands is presented. With the help of synchrotron radiation, x-ray diffraction intensity mapping in reciprocal space has been measured during growth. The internal strain distribution and height of the Stranski-Krastanov islands were monitored at a temporal resolution of 9.6 s. The relaxation process of internal strain inside the Stranski-Krastanov islands displayed significant dependence on the growth temperature.

Authors:
; ;  [1]
  1. Synchrotron Radiation Research Center, Japan Atomic Energy Research Institute, Mikazuki-cho, Hyogo 679-5148 (Japan)
Publication Date:
OSTI Identifier:
20778783
Resource Type:
Journal Article
Resource Relation:
Journal Name: Applied Physics Letters; Journal Volume: 88; Journal Issue: 10; Other Information: DOI: 10.1063/1.2186106; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CRYSTAL GROWTH; DISTRIBUTION; GALLIUM ARSENIDES; INDIUM ARSENIDES; MAGNETIC ISLANDS; MAPPING; MOLECULAR BEAM EPITAXY; QUANTUM DOTS; RESOLUTION; SEMICONDUCTOR MATERIALS; STRAINS; STRESS RELAXATION; SYNCHROTRON RADIATION; X-RAY DIFFRACTION

Citation Formats

Takahasi, Masamitu, Kaizu, Toshiyuki, and Mizuki, Jun'ichiro. In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001). United States: N. p., 2006. Web. doi:10.1063/1.2186106.
Takahasi, Masamitu, Kaizu, Toshiyuki, & Mizuki, Jun'ichiro. In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001). United States. doi:10.1063/1.2186106.
Takahasi, Masamitu, Kaizu, Toshiyuki, and Mizuki, Jun'ichiro. Mon . "In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001)". United States. doi:10.1063/1.2186106.
@article{osti_20778783,
title = {In situ monitoring of internal strain and height of InAs nanoislands grown on GaAs(001)},
author = {Takahasi, Masamitu and Kaizu, Toshiyuki and Mizuki, Jun'ichiro},
abstractNote = {A monitoring technique for molecular beam epitaxial growth of InAs/GaAs(001) nanoislands is presented. With the help of synchrotron radiation, x-ray diffraction intensity mapping in reciprocal space has been measured during growth. The internal strain distribution and height of the Stranski-Krastanov islands were monitored at a temporal resolution of 9.6 s. The relaxation process of internal strain inside the Stranski-Krastanov islands displayed significant dependence on the growth temperature.},
doi = {10.1063/1.2186106},
journal = {Applied Physics Letters},
number = 10,
volume = 88,
place = {United States},
year = {Mon Mar 06 00:00:00 EST 2006},
month = {Mon Mar 06 00:00:00 EST 2006}
}
  • Strain in thin layers of molecular-beam epitaxy (MBE) grown InAs on GaAs(001) was characterized by both Raman spectroscopy and double crystal x-ray diffraction (DCD). The goal of this study was to evaluate the use of Raman spectroscopy as a method of strain determination and compare it to DCD. Recent results of Burns et al., for In/sub x/Ga/sub 1-//sub x/As proved that Raman spectroscopy could be an important in situ analysis method for MBE (G. Burns, C. R. Wie, F. H. Dacol, G. D. Pettit, Appl. Phys. Lett. 51, 1919 (1987)). We find that Raman spectroscopy has several advantages over DCD.more » Raman data samples the stress in a much thinner volume than DCD, allowing one to determine when a surface layer of the thin film is no longer under stress. Films that are highly lattice mismatched with the substrate have a large number of defects at the substrate/epilayer interface. Raman analysis determines straain in a more defect free layer of these films when the layer thickness is greater than t/sub c/, the critical thickness. DCD samples an average strain over the entire thickness of most semiconductor films. There are several disadvantages in the use of Raman spectroscopy as a strain analysis method. We found that the materials parameters of InAs required to calculate the strain from the shift in the optical phonon energy of the epilayer were not accurately known. Quantitative strain determination by Raman spectroscopy depends on accurate values of the phonon deformation potentials of InAs and other III--V compounds of interest. Also, DCD is capable of determining much smaller strains than Raman spectroscopy.« less
  • Photoluminescence (PL) at wavelengths over 1.55 μm from self-assembled InAs quantum dots (QDs) grown on GaAs(001) is observed at room temperature (RT) and 4 K using a bilayer structure with thin cap. The PL peak has been known to redshift with decreasing cap layer thickness, although accompanying intensity decrease and peak broadening. With our strain-controlled bilayer structure, the PL intensity can be comparable to the ordinary QDs while realizing peak emission wavelength of 1.61 μm at 4 K and 1.73 μm at RT. The key issue lies in the control of strain not only in the QDs but also in the cap layer. By combiningmore » with underlying seed QD layer, we realize strain-driven bandgap engineering through control of strain in the QD and cap layers.« less
  • 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 amore » 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.« less
  • The in-plane optical anisotropy (IPOA) in (001)-grown GaAs/AlGaAs quantum wells (QWs) with different well widths varying from 2 nm to 8 nm has been studied by reflectance difference spectroscopy. Ultra-thin InAs layers with thickness ranging from 0.5 monolayer (ML) to 1.5 ML have been inserted at GaAs/AlGaAs interfaces to tune the asymmetry in the QWs. It is demonstrated that the IPOA can be accurately tailored by the thickness of the inserted ultra-thin InAs layer at the interfaces. Strain-induced IPOA has also been extracted by using a stress apparatus. We find that the intensity of the strain-induced IPOA decreases with the thickness ofmore » the inserted InAs layer, while that of the interface-induced IPOA increases with the thickness of the InAs layer. Theoretical calculations based on 6 band k ⋅ p theory have been carried out, and good agreements with experimental results are obtained. Our results demonstrate that, the IPOA of the QWs can be greatly and effectively tuned by inserting an ultra-thin InAs layer with different thicknesses at the interfaces of QWs, which does not significantly influence the transition energies and the transition probability of QWs.« less
  • We studied the structural and photoluminescence (PL) characteristics of InAs quantum dots (QDs) grown on nitrogen (N) δ-doped GaAs(001). The emission wavelength for low-density N-δ doping exhibited a blueshift with respect to that for undoped GaAs and was redshifted with increasing N-sheet density. This behavior corresponded to the variation in the In composition of the QDs. N-δ doping has two opposite and competing effects on the incorporation of Ga atoms from the underlying layer into the QDs during the QD growth. One is the enhancement of Ga incorporation induced by the lattice strain, which is due to the smaller radiusmore » of N atoms. The other is an effect blocking for Ga incorporation, which is due to the large bonding energy of Ga-N or In-N. At a low N-sheet density, the lattice-strain effect was dominant, while the blocking effect became larger with increasing N-sheet density. Therefore, the incorporation of Ga from the underlying layer depended on the N-sheet density. Since the In-Ga intermixing between the QDs and the GaAs cap layer during capping also depended on the size of the as-grown QDs, which was affected by the N-sheet density, the superposition of these three factors determined the composition of the QDs. In addition, the piezoelectric effect, which was induced with increased accumulation of lattice strain and the associated high In composition, also affected the PL properties of the QDs. As a result, tuning of the emission wavelength from 1.12 to 1.26 μm was achieved at room temperature.« less