Abstract
We report the growth mechanism and optical characteristics of type-II band-aligned GaSb quantum dots (QDs) grown on GaAs using droplet epitaxy-driven nanowire formation mechanism in with molecular beam epitaxy (MBE). Using transmission electron microscope (TEM) and scanning electron microscope (SEM) images, we confirmed that the QDs, which comprise zinc-blende crystal structures with hexagonal shape, were successfully grown through the formation of a nanowire from a Ga droplet with less strain between GaAs and GaSb. Photoluminescence (PL) peaks of GaSb, which are capped by the GaAs layer, are observed at 1.11 eV, 1.26 eV, and 1.47 eV, assigned to the QDs, a wetting-like layer (WLL), and bulk GaAs, respectively, at the measurement temperature of 14 K and excitation laser power of 30 mW. The integrated PL intensity of the QDs is significantly stronger than the WLL, which indicates well-grown GaSb QDs on GaAs and the generation of an interlayer exciton, as shown in the power and temperature-dependent PL, respectively. In addition, Time-resolved PL (TRPL) data show that the GaSb QD and GaAs layer form a self-aligned type-II band alignment, and temperature-dependent PL data exhibit a high equivalent internal quantum efficiency of 15+/-0.2%.
Modification of band alignment at interface of AlyGa1-ySb/AlxGa1-xAs type-II quantum dots by concentrated sunlight in intermediate-band solar cells with separated absorption and depletion regions