Surface Morphology and Island Shape of MOVPE Grown InGaN Nano-Island Ensembles Studied by STM

The dependence of the InGaN/GaN(0001) surface morphology on the growth parameters of metal organic vapour phase epitaxy (MOVPE) at 650°C has been investigated using scanning tunneling microscopy. After deposition of InGaN under In-rich growth conditions, a preferential nucleation of islands at defects of the GaN substrate film is found. The islands have a large size (diameter ~ 80 nm, height ~10 nm) and show a spiral disc-like shape with an atomically flat surface, and the wetting layer surface appears very smooth. For thicker InGaN layers, In-droplets are formed on top of the large islands and the wetting layer becomes rougher. For InGaN growth at a reduced In partial pressure, hexagonal islands with an atomically flat top surface are formed and pyramidal islands of triangular base with smooth side facet structures are observed. The effects of growth rate and V/III flux ratio on the InGaN surface morphology have also been studied and the results indicate that a slower growth reduces the large island formation probability whereas a high V-III flux ratio enhances it. All findings are discussed in terms of thermal diffusion, In-incorporation and thermal decomposition.