Helical-type surface defects in GaN and InGaN thin films epitaxially grown on GaN templates at reduced temperatures

Abstract

The surface morphologies of GaN and InGaN films grown at 780degreesC by metalorganic vapor phase epitaxy were determined using atomic force microscopy. A qualitative model is presented to explain observed instabilities in the step morphology of these films, namely, the formation of hillock islands and v-defects that give rise to surface roughening. The latter are a result of a boundary dragging effect, where interactions occur between the movement of homogeneous and heterogeneous steps and the tendency to form atom clusters in the terrace in the transition in kinetic growth regime. The tendency to form v-defects was associated with dislocation density. A delay in the formation of v-defects in InGaN was observed and associated With the ammonia partial pressure and the interactions between hillock islands and pure screw or mixed dislocations. Hillock island formation was attributed to a transition in thermodynamic mode to three-dimensional island growth. Explanations for the foregoing observations are based on growth model theory previously developed by Burton, Cabrera, and Frank (BCF) and on changes in the surface kinetics with temperature, In composition, and gas phase composition.