Effects of Interface Grading on Electronic States in Columnar Type-II Quantum Dots

Abstract

Columnar type-II GaSb quantum dots (QDs) in GaAs are studied theoretically to clarify how electronic states are affected by the interface grading caused by the interdiffusion of Sb and As. Truncated-cone-shaped QD stacks are analyzed as a function of the diffusion length Ld, where the stacking dot number N is varied from 1 to 4. The energies of heavy- and light-hole ground states Ehh and Elh, respectively are calculated. The heavy hole is the lowest state when N = 1 and 2, and Elh is lower than Ehh for N = 4. When N = 3, the lowest state changes from light holes to heavy holes as Ld increases. We also evaluate the overlap Θ between the electron and hole wave functions, which determines the strength of optical transition. It is found that Θ changes by 2–3 orders of magnitude depending on N and Ld.