Elastic stress and emission nonhomogeneity in asymmetric InAs quantum dot in a well structures

Photoluminescence (PL) and X-ray diffraction (XRD) have been studied in InAs quantum dots (QDs) embedded in asymmetric GaAs/In_xGa_1-xAs/In_0.15Ga_1-0.15As/GaAs quantum wells (dot-in-a-well, DWELL) with the parameter x=0.10-0.25. The parameter x increasing in the capping layer is accompanied by the non monotonous variation of InAs QD parameters. The PL intensity increases and the PL peak shifts to low energy in structures with x=0.15. On the contrary the structures with x=0.20 and 0.25 are characterized by lower PL intensities and PL peak positions shifted to higher energy. The method of X-ray diffraction has been applied with the aim to study the variation of elastic strain in asymmetric DWELL structures. It was shown that the minimum of elastic strain corresponds to DWELL with x=0.15. In DWELLs with x=0.20 and 0.25 the level of compressive strain increases. The reasons of strain variation are discussed as well.