Selective Area Growth of GaN Nano Islands by Metal Organic Chemical Vapor Deposition: Experiments and Computer Simulations

Abstract

ABSTRACTWe report the properties of GaN islands selectively grown by MOCVD on (0001) GaN/sapphire templates and on bare (0001) sapphire substrates. The approach allows us to grow GaN crystals with control over size and density through optical (micro-scale) and e-beam (nano-scale) lithography, and control over shape through MOCVD growth parameters. We have obtained complete pyramidal and prismatic hexagonal GaN islands. The growth characteristics are found to be very different from what we obtain for epitaxial layers, an effect which is attributed to micro/nanoloading and surface diffusion of source materials on the hard mask. From the dependence of growth rate of the pyramids with pitch we evaluate Ga surface diffusion length of ∼ 10 μm over SiO2 mask. We present a growth model based on diffusion and discuss the results of modeling with experimental data. Using micro-Raman spectroscopy the stress in pyramidal and prismatic islands was evaluated to be 20 MPa and 85 MPa, respectively. This implies that the selectively grown islands are relatively more relaxed compared to similar thickness of uniform layers. Micro catholdoluminescence (CL) shows a narrow line width and a better quality of GaN nano islands grown on e-beam lithography patterned templates. The GaN islands, of varying shapes, were overgrown with InGaN multiple quantum wells, which showed a few times stronger micro-CL emission than from GaN.