Emission and strain in InGaAs/GaAs quantum wells with InAs quantum dots obtained at different temperatures

The photoluminescence (PL), its temperature dependence and X ray diffraction (XRD) have been studied in the symmetric In _0.15Ga _0.85As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs), obtained with the variation of QD growth temperatures (470-535°C). The increase of QD growth temperatures is accompanied by the enlargement of QD lateral sizes (from 12 up to 28 nm) and by the shift non monotonously of PL peak positions. The fitting procedure has been applied for the analysis of the temperature dependence of PL peaks. The obtained fitting parameters testify that in studied QD structures the process of In/Ga interdiffusion between QDs and capping/buffer layers takes place partially. However this process cannot explain the difference in PL peak positions. The XRD study has revealed the high intensity peaks which correspond to the diffraction of X ray line from the (2 0 0) crystal planes of cubic GaAs. It was shown that the XRD peak is the superposition of the diffraction from the GaAs substrate and GaAs layers of quantum wells. The position of diffraction peaks related to the cubic GaAs substrate coincides with the very well-known XRD data for the bulk GaAs. At the same time the (2 0 0) diffraction peaks in GaAs epitaxial layers shift to the high angles in comparison with the bulk GaAs, testifying the compression strain in GaAs epitaxial layers. The value of elastic strain has been estimated. The minimum of elastic strain is detected in the structure with QD grown at 510°C that manifests itself by the higher QD PL intensity and lower PL peak energy.