InGaAs nanostructures grown by droplet molecular beam epitaxy

Abstract

InGaAs ring-shaped nanostructures are fabricated by droplet epitaxy technique using solid source molecular beam epitaxy (MBE). InGa droplet forming conditions have been varied in order to investigate the effect of substrate temperature during InGa deposition and deposited amount of indium (In) and Gallium (Ga) on InGaAs ring-structures. It was found that increasing substrate temperature during InGa deposition resulted in InGaAs rings larger size but lower density since greater diffusion length of metallic In and Ga atoms responsed to 2-dimensional expansion of InGa droplets and coalescence of neighbouring droplets. Also, the increasing InGa amount deposited would result in InGaAs rings larger size. The ring density is also increased when increasing InGa amount between 2-3 ML. However, when increasing InGa amount to 4 ML, the density becomes to decreased. The density is increased again while increasing InGa amount to 5 ML. It was supposed that decrease of ring density was caused from formation of InGa full-layer instead of individual droplets when greater amount of InGa was deposited. Subsequently, newly supplied InGa adatoms would from the droplets above the layer resulting in renewal of the number of the droplet formed. For photoluminescence (PL) measurement, the nanostructures were repeatedly grown under selected droplet forming condition with additional 100-nm GaAs capping layers including GaAs layers grown by migration-enhanced epitaxy and conventional GaAs layers. The analytical optical properties of InGaAs rings are confirmed by the PL spectra of capped InGaAs ring-structures at 77 K. The PL result indicates the high quality crystal. However, PL intensity was found to be low resulting from low density of the ring structures (10 [superscript 8] cm [superscript -2]).