Elastic Energy in Inas Quantum Dot-in-a-Well Structures

Abstract

The photoluminescence (PL), its temperature dependence and X ray diffraction (XRD) have been studied in the symmetric In0.15Ga1-0.15As/GaAs quantum wells (QWs) with embedded InAs quantum dots (QDs), obtained with the variation of QD growth temperatures (470-535oC). 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 monotonically of PL peak positions. The fitting procedure has been applied on the base of Varshni analysis to the temperature dependences of PL peaks. The obtained Varshni 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 at 2Θ= 31.6-31.8o (Kα1, Kα2) that correspond to the X ray diffraction of the Kα1 and Kα2 lines of Cu source from the (200) 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 know XRD data for the bulk GaAs. It means that the elastic strain in the GaAs substrate has been relaxed. At the same time the peak positions of the (200) 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 minimum of elastic strain is detected in the structure with QD grown at 510oC that manifests itself by the higher QD PL intensity and lower the PL peak energy.