Strain relaxation in InAs quantum dots through capping layer variation and its impact on the ultrafast carrier dynamics

Abstract

Ultrafast carrier dynamics is found to be crucial for influencing the efficiency of quantum dot (QD)-based optoelectronic devices. Here, we have studied picosecond resolved dynamics in InAs semiconductor quantum dots forming various heterostructure geometries with their different capping layers. The carriers (electron-hole pairs) are optically injected into three dimensional heterostructure barriers after which, we monitor the carrier relaxation into the zero-dimensional InAs dots by using picosecond resolved time correlated single photon counting technique. We have explicitly investigated and analyzed the effect of three different capping layers, GaAs (binary), In0.15Ga0.85As/GaAs (ternary) and In0.21Al0.21Ga0.58As/GaAs (quaternary) offering various optical properties of InAs quantum dots. It has been observed that quaternary strain reducing layer effectively suppresses Indium migration from the QDs and enhances the confinement of carriers inside the QD heterostructures. In this study, we also find that thermal stability of the carriers is improved in the quaternary capped QDs more effectively compared to the conventional binary and ternary capped one. In brief, our experiments provide essential insight into carrier relaxation in the InAs QDs across various capping layers.