Nucleation and Coalescence of Indium Rich InGaN Layers on Nitridated Sapphire in Metal–Organic Vapor Phase Epitaxy

Abstract

We report on the evolution of N-polar wurtzite (0001̄) InGaN layers with high indium content grown directly on nitridated (0001) sapphire by metal–organic vapor phase epitaxy. In-situ ellipsometry showed an initial growth delay of 5–8 nm for layers with more than 45% indium content. Atomic force microscopy showed small dense islands which reached their final size after 5–8 nm deposition. The roughness saturated only after 15 nm, and the width of the X-ray diffraction (00.2) reflex showed a similar behavior. Therefore, N-polar InGaN grows via nucleation (d < 10 nm) followed by coalescence (d < 20 nm). With less than 40% indium the coalescence is much slower, very similar to Ga-polar (0001) GaN despite N-polarity of the InN layers. This indicates towards a surface transition between 40 and 50% indium content.