Chareterization of GaN/InGaN hetero-structures by SEM and CL

GaN and InGaN epilayers were deposited on (0001) sapphire in a vertical reactor using Ammonia, TMG and TMI precursors. Smooth GaN layers (roughness <5 nm) were obtained for growth at 1080°C, while depositions at higher temperatures gave rougher surfaces. The cathodoluminescence (CL) investigation showed that rougher GaN layers are also less uniform from the point of view of optical emission. Two main luminescence peaks (at about 358 nm and 378 nm) were observed in most films, but their spatial correlation and relative intensity were seen to change according to surface roughness. All tested samples were free from yellow band. InGaN samples (with an In fraction of 14%) appeared to be more uniform in terms of luminescence at the microscopic scale.