Carrier relaxation bottleneck in type-II InAs/InGaAlAs/InP(001) coupled quantum dots-quantum well structure emitting at 1.55 μm

Abstract

Carrier relaxation in self-assembled InAs/In0.53Ga0.23Al0.24As/InP(001) quantum dots emitting at 1.55 μm and quantum dots coupled to the In0.64Ga0.36As/In0.53Ga0.23Al0.24As quantum well through a thin In0.53Ga0.23Al0.24As barrier is investigated employing high-temporal-resolution (< 0.3 ps), time-resolved spectroscopic techniques at cryogenic temperatures, supported additionally with photoluminescence, photoluminescence excitation, and theoretical modelling. We focused on intra-band carrier relaxation pathways that solely determine the observed non-equilibrium carrier population kinetics. We ascertained relatively fast carrier capture and intra-band relaxation process in a reference structure with quantum dots only (∼8 ps time constant) and even faster initial relaxation in the coupled system (∼4 ps). An evident bottleneck effect is observed for the final relaxation stage in the coupled quantum dots-quantum well system slowing down the overall relaxation process by a factor of 5. The effect is attributed to a peculiar picture of the confined conduction band states in the coupled system exhibiting significant changes in the spatial distribution between the relevant lowest-lying electronic states.