Effects of Sb/As intermixing on optical properties of GaSb type-II quantum dots in GaAs grown by droplet epitaxy

Abstract

Optical properties of GaSb type-II quantum dots (QDs) in GaAs were studied and compared with a theoretical model to clarify how the spatial overlap of holes in the dot and electrons outside is affected by the interdiffusion of Sb and As. GaSb QDs were grown in a GaAs substrate by droplet epitaxy and annealed at the temperature Ta=650–850 °C to induce the Sb/As intermixing. Photoluminescence (PL) studies showed that the integrated PL intensity I decreases to less than 1/10 as Ta is raised from 650 to 750 °C, while I increases by three orders of magnitude with the increase of Ta from 750 to 850 °C. This behavior is explained by the overlap Θ between electron and hole wave functions; in an initial stage of the interdiffusion, the mixing occurs only near the dot/matrix boundary, leading to the decrease in the overlap Θ, since electrons are more repelled by the dot. In later stages, however, the hole confinement and the electron repulsion in the dot both weaken, leading to the increase in the overlap Θ.