Effects of Interface Grading on Electronic States and Optical Transitions in GaSb Type-ll Quantum Dots in GaAs

摘要

Electronic states in type-ll GaSb quantum dots (QDs) in GaAs are studied theoretically and compared with experiments to clarify how the spatial overlap of holes in the dot and electrons outside is affected by the interface grading caused by the interdiffusion of Sb and As. Cone-shaped QDs with the initial size of 6 nm height and 20 nm radius are analyzed. The wavefunctions of electrons and holes and their overlap Θ are calculated. In an initial stage of grading, when the grading length L_g is below 1.2 nm, the mixing occurs only near the dot/matrix interface, leading to a decrease in Θ, since holes are squeezed into a smaller volume whereas electrons are more repelled by the dot. In later stages where L_g exceeds 1.2 nm, however, the hole confinement and the electron repulsion by the dot both weaken, leading to an increase in Θ; this accounts for a recent finding that the annealing of GaSb QDs induces a blue shift and an intensity increase in photoluminescence spectra.