Ameliorating the optical and structural properties of InAs quantum dot heterostructures through digital alloy capping materials: Theory and experiment

Abstract In this study, we have employed a unique technique called digital alloy capping to grow the strain reducing capping layer on InAs quantum dots (QDs). Four different capping materials have been considered, i.e. two ternary (InxGa1-xAs and GaAs1-xSbx) and two quaternary (InxAlyGa1-x-yAs and InxGa1-xAs1-ySby) alloys. Experimental investigations are carried out for InAs QDs capped with InGaAs capping material along with a detailed theoretical study of other capping materials. Distinct short period superlattices are grown with different compositions of capping materials namely digital alloy capping layer (DACL) with specific thicknesses, instead of a thick capping material (namely analog alloy capping layer (AACL)). The compositions of capping material in DACL structures is chosen in a way to minimize the lattice mismatch within the interfaces of QD layer, sub-capping layers and top GaAs layer. QDs capped with DACL provide reduced strain, and emission at telecommunication wavelengths which are confirmed from the experimental and simulation studies. The biaxial and hydrostatic strain has been computed to understand the strain distribution within the heterostructures. This study unveils the effectiveness of the DACL over AACL, and therefore motivates to design futuristic optoelectronic devices with this technique.