Effect of Thermal Annealing on Absorption and Hole Escape Processes in Type II GaSb/GaAs Quantum Dots: Implications for Solar Cell Design

Abstract

We present a theoretical study of the rapid thermal annealing process and strain on the electronic, optical, and charge dynamical properties of type II GaSb/GaAs quantum dots (QDs). Our theoretical results show a blueshift and the enhancement of interband absorption spectrum because of inter-diffusion processes and the annealed samples. We have identified that increased annealing temperature makes the hole escape times from such QD shorter while the effect of strain on the hole confinement potential becomes weaker. At the same time, in both structures, unstrained and strained QDs, the intra-band absorption in the valence band (IVBA) is redshifted, and its magnitude is decreased after annealing when compared with the as-grown sample. To explain those effects we discuss how the electron–hole wave function overlap varies with thermal treatment and strain and discussed those effects on radiative and thermal processes. Our results explain and are in agreement with the recent experimental observations on similar structures. We have identified that holes could thermally escape out of the type II GaSb/GaAs QD before they are recombined and will contribute to the enhancement in absorption of QD solar cells. The emission and tunneling times of holes were estimated to be $ 10^{-12}$ to $10^{-14}$ s about one order of magnitude faster than the escape times because of radiative recombination processes, $ 10^{-11}$ to $10^{-13}$ s.