Abstract
We report the growth mechanism and optical characteristics of type-II band-aligned GaSb quantum dots (QDs) grown on GaAs using a droplet epitaxy-driven nanowire formation mechanism with molecular beam epitaxy. Using transmission electron microscopy and scanning electron microscopy images, we confirmed that the QDs, which comprised zinc-blende crystal structures with hexagonal shapes, were successfully grown through the formation of a nanowire from a Ga droplet, with reduced strain between GaAs and GaSb. Photoluminescence (PL) peaks of GaSb capped by a GaAs layer were 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 was significantly stronger than that of the WLL, which indicated well-grown GaSb QDs on GaAs and the generation of an interlayer exciton, as shown in the power- and temperature-dependent PL spectra, respectively. In addition, time-resolved PL data showed that the GaSb QD and GaAs layers formed a self-aligned type-II band alignment; the temperature-dependent PL data exhibited a high equivalent internal quantum efficiency of 15 ± 0.2%.
Highlights
Group III–V materials with direct bandgaps have been actively studied as novel photonic materials because their electrical and optical characteristics can be controlled by changing their structure and dimensions[1,2,3,4]
We investigated the growth mechanism of type-II GaSb quantum dots (QDs) grown on GaAs using a self-grown nanowire process
A Ga droplet was formed on top of the GaAs layer, and a hexagonal GaSb QD with a zinc-blende structure grew through a nanowire growth mechanism by the diffusion of Sb into the Ga droplet
Summary
GaSb QDs were grown on n-type GaAs (001) wafers using an MBE system. First, to reduce the native defects on the GaAs substrate, we sequentially grew a 200-nm-thick GaAs buffer, a short-period superlattice (SPS) structure with two alternate layers (5 nm-thick A l0.3Ga0.7As and 5-nm thick GaAs), and a 75-nm-thick GaAs layer at a growth temperature of 580 °C13–15. GaAs was grown on top of the surface at 280 °C to prevent the GaSb QDs from melting without stopping the growth of the capping layer. A 40-nm-thick Sb layer was deposited on the GaAs surface, confirmed by the cross-sectional energy-dispersive X-ray (EDX) analysis of the outside of the QDs, as shown in Supporting Figure S3, where GaSb nanowires were grown under the growth conditions of the diffusion-limited process for the Sb atom. 14K 30K 40K 50K 60K 70K 80K 90K 105K 130K 160K 180K 200K 220K 240K 260K 280K 300K (d)
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