Highly luminescent cubic GaN microcrystals grown on GaAs(001) substrates by RF-MBE

Cubic GaN microcrystals have been grown on a cubic GaN template by radio-frequency plasma molecular beam epitaxy (RF-MBE) using a relatively thin low-temperature-grown GaN buffer layer, which promotes the generation of Ga droplets acting as the nuclei for three-dimensional (3D) growth. These crystals are found to be highly luminescent compared to those grown by metalorganic vapour-phase epitaxy (MOVPE). Their optical quality is much better than that of the two-dimensionally (2D) growth c-GaN region as investigated by microcathodoluminescence (micro-CL) and photoluminescence (PL). These results suggest that defects or local strain, originating from the large lattice mismatch and thermal mismatch between GaN and GaAs, could be avoided by the transition from 2D to 3D growth mode with the use of this nucleation process.