Effects of thermal annealing and strain on type-II to type-I band alignment transition in InAs/GaAsSb quantum dots

Abstract

We conducted a theoretical investigation into the impact of thermal annealing on the emission properties of type-II InAs quantum dots (QDs) embedded in GaAsSb barriers. We examined how the lattice-mismatch strain and charge carriers confinement profiles affect the excitonic transition energy and radiative lifetime. The In/Ga interdiffusion between the QD and barrier materials was first modeled using Fickian diffusion. Our findings show that annealing affects both the composition and size of QDs, thus improving their uniformity. Next, we analyzed the influence of strain reduction on carrier confinement potentials during annealing by solving the Schrödinger equation separately for charge carriers. The importance of strain on the QD potential profile and carrier spatial distribution was investigated. We predict a transition from type-II to type-I QDs at a critical temperature, $T_a^C=800°C$, which is in agreement with experimental results. Finally, we estimate a reduction in excitonic radiative lifetime from 10 $ns$ (type-II) to 1 $ns$ (type-I), which is consistent with prior experimental studies. Our results demonstrate that thermal annealing increases radiative recombination rates while decreasing localized states in the GaAsSb layer. This study demonstrates the ability to control the transition between type-II and type-I band alignments in annealed QDs, making them promising for use in solar cells.