Indium rich clusters in MOCVD InGaN/GaN: high resolution electron microscopy study and finite element modelling

The Indium (In) composition was investigated in InGaN/GaN metal-organic chemical vapour deposition quantum wells by measurement of the local lattice distortion in high-resolution electron microscopy images. Experimental results were compared with the strain field measured on the simulated images of In-rich clusters. The atom positions in the supercell used for image simulations were generated by three dimensional finite element modelling. The active areas of the GaN-based light-emitting diodes and laser diodes are made of GaN/InGaN quantum wells and many reports suggest that their high-efficiency luminescence may be due to In clustering. One of the most powerful techniques for chemical composition determination is the measurement of the tetragonal distortion from cross-sectional high-resolution electron microscopy images. The presence of In-rich clusters leads to local lattice distortion, inhomogeneous relaxation at the thin film surface and strong atomic column curvature.