Investigation of strain in self-assembled multilayer InAs/GaAs quantum dot heterostructures

The self-assembled InAs/GaAs multilayer quantum dots (QDs) are formed in a strain-driven process due to the lattice mismatch of the InAs/GaAs system. We have investigated strain interaction in 10 layer QD heterostructure with varying thicknesses of combination capping (InAlGaAs and GaAs) by means of scanning transmission electron microscopy (STEM), high-resolution X-ray diffraction (HRXRD) and Raman scattering. STEM micrographs reveal nice stacking of defect-free dots in all the layers of the sample having a thick combination capping. The periodic satellite peaks in the HRXRD rocking curve show good formation of dots and an indication of reduced compressive strain in the heterostructure with increased capping thickness. We detect an upward phonon frequency shift for InAs QDs in the low-temperature Raman study, which is believed to be due to strain relaxation as the thickness of the capping layer increases. The sample with thick combination capping showed better optical emission properties.