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Title: InGaN Selfassembled Quantum Dots Investigated By X-Ray Diffraction-Anomalous-Fine Structure Technique

Abstract

Local chemical composition of InGaN quantum dots grown by molecular-beam epitaxy on GaN virtual substrates was investigated by x-ray diffraction anomalous fine-structure method. Using this approach, we found that the In content increases from 20% at the dot base to 40-50% at the top. From the detailed numerical analysis of the data we were able to reconstruct the local neighborhood of Ga atoms in different positions in the dots, as well as the local elastic relaxation state.

Authors:
 [1];  [2]; ; ; ; ;  [3];  [4]
  1. Institute of Physics, Polish Academy of Sciences, Al. Lotnikow 32/46, 02668 Warsaw (Poland)
  2. Charles University, Faculty of Mathematics and Physics, Ke Karlovu 5, 121 16 Prague (Czech Republic)
  3. Institute of Solid State Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen (Germany)
  4. ESRF, 6 rue Jules Horowitz, BP220, 38043 Grenoble CEDEX (France)
Publication Date:
OSTI Identifier:
21055065
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 893; Journal Issue: 1; Conference: ICPS 2006: 28. international conference on the physics of semiconductors, Vienna (Austria), 24-28 Jul 2006; Other Information: DOI: 10.1063/1.2729779; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ATOMS; CHEMICAL COMPOSITION; CRYSTAL GROWTH; FINE STRUCTURE; GALLIUM NITRIDES; INDIUM NITRIDES; MOLECULAR BEAM EPITAXY; NUMERICAL ANALYSIS; QUANTUM DOTS; RELAXATION; SEMICONDUCTOR MATERIALS; SUBSTRATES; X-RAY DIFFRACTION

Citation Formats

Piskorska, E., Holy, V., Siebert, M., Schmidt, T., Falta, J., Yamaguchi, T., Hommel, D., and Renevier, H. InGaN Selfassembled Quantum Dots Investigated By X-Ray Diffraction-Anomalous-Fine Structure Technique. United States: N. p., 2007. Web. doi:10.1063/1.2729779.
Piskorska, E., Holy, V., Siebert, M., Schmidt, T., Falta, J., Yamaguchi, T., Hommel, D., & Renevier, H. InGaN Selfassembled Quantum Dots Investigated By X-Ray Diffraction-Anomalous-Fine Structure Technique. United States. doi:10.1063/1.2729779.
Piskorska, E., Holy, V., Siebert, M., Schmidt, T., Falta, J., Yamaguchi, T., Hommel, D., and Renevier, H. Tue . "InGaN Selfassembled Quantum Dots Investigated By X-Ray Diffraction-Anomalous-Fine Structure Technique". United States. doi:10.1063/1.2729779.
@article{osti_21055065,
title = {InGaN Selfassembled Quantum Dots Investigated By X-Ray Diffraction-Anomalous-Fine Structure Technique},
author = {Piskorska, E. and Holy, V. and Siebert, M. and Schmidt, T. and Falta, J. and Yamaguchi, T. and Hommel, D. and Renevier, H.},
abstractNote = {Local chemical composition of InGaN quantum dots grown by molecular-beam epitaxy on GaN virtual substrates was investigated by x-ray diffraction anomalous fine-structure method. Using this approach, we found that the In content increases from 20% at the dot base to 40-50% at the top. From the detailed numerical analysis of the data we were able to reconstruct the local neighborhood of Ga atoms in different positions in the dots, as well as the local elastic relaxation state.},
doi = {10.1063/1.2729779},
journal = {AIP Conference Proceedings},
number = 1,
volume = 893,
place = {United States},
year = {Tue Apr 10 00:00:00 EDT 2007},
month = {Tue Apr 10 00:00:00 EDT 2007}
}
  • 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 structuremore » 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.« less
  • The relevance of grazing-incidence anomalous diffraction as a tool to investigate the strain and structure of small-size embedded nano-objects is examined. Multiple scattering effects, originating from the grazing-incidence setup, are analyzed with a special emphasis on the cusp of the diffraction anomalous spectrum and the extended diffraction anomalous fine-structure oscillations. It is shown that even for grazing-incidence angle, a Born approximation treatment is justified for quantum dots (QDs) on top of a thin wetting layer. The discussion focuses on the overgrowth of AlN on top of GaN QDs. Both the in-plane and out-of-plane strains in the dots can be specificallymore » determined, by extracting the Ga partial scattering amplitude from measurements of the scattered intensity along both the in- and out-of-plane directions, close to the (3030) and (3032) reflections, at several energies across the Ga K edge. The study is complemented by the analysis of the local environment of Ga atoms in the dots through the measurement of the fine-structure oscillations in diffraction condition. The oscillations are found almost insensitive to the grazing-incidence multiple-scattering effects. Accordingly, the out-of-plane strain and possible intermixing specifically in the dots can be deduced. The QDs are shown to remain pure GaN all along the capping process. The QDs strain state exhibits a larger strain relaxation than expected from an elastic model, suggesting the presence of a plastic strain relaxation, possibly through dislocations at the vicinity of the QDs. Finally, the influence of the substrate as regards strain relaxation in the QDs is discussed by comparing our results to those we previously obtained for a series of samples grown on AlN/sapphire.« less
  • We have investigated the local atomic environment of the Ga atoms in an InxGa1-xN single quantum well structure using Optically Detected Extended X-ray Absorption Fine Structure (OD-EXAFS). A comparison of the OD-EXAFS data with a theoretical model shows the technique to be site selective for this particular structure and reveals that the quantum well emission originates from regions with x=0.15.
  • Capping of GaN quantum dots with AlN has been studied at the monolayer scale by combining atomic force microscopy, high resolution electron microscopy, and grazing incidence x-ray anomalous diffraction. Consistent with the results provided by these three techniques, it has been demonstrated that, following a wetting of the dots by an AlN layer up to 4 ML coverage, subsequent capping is dominated by a preferential AlN growth in between the dots, eventually resulting in a complete smoothing of AlN. Interdiffusion has been shown to be negligible during this process, which makes the GaN/AlN system unique among semiconductors.
  • Copper oxide quantum dots (CuOQD) were grown in various thicknesses on different SrTiO3(001) surfaces and were investigated by near edge x-ray absorption fine structure (NEXAFS) spectroscopy. The experimental growth conditions for the CuOQD were optimized to obtain Cu2O as the major phase. The CuOQD grown on clean SrTiO3(001) surfaces at 825 K or higher with p(O2) of 9.0x10-7 Torr or above contain mostly CuO contrasting to CuOQD grown at 800 K with p(O2) of {approx}7.0x10-7 Torr that contain primarily Cu2O. Furthermore, it is established that there is a strong interaction between the SrTiO3(001) surface and the first few monolayers ofmore » the CuOQD, which induces the formation of Cu(II). However, this interaction is mitigated with increasing thickness of CuOQD resulting in the exclusive formation of Cu2O in the topmost layers. The influence of the SrTiO3(001) substrate on the formation of CuOQD can be reduced by modifying the substrate surface using chemical treatment and/or energetic Au2? ion-beam irradiation, since the substrate effect results from the reaction between the substrate oxygen and the copper atoms from the CuOQD. Examination of the photochemical properties of these CuOQD shows that prolonged soft x-ray irradiation under vacuum reduces Cu(II), which is present as a minor impurity in the CuOQD.« less