Coalescence aspects of III-nitride epitaxy

Abstract

In this work, coalescence aspects of wurtzite-III-nitride epitaxy are addressed. The coalescence phenomena have been studied in thin epilayers by means of electron and atomic force microscopies, and electron and x-ray diffractions. This study generalizes the growth parameters responsible for the rapid coalescence of III-nitride films, and describes the coalescence qualitatively and, partly, analytically for the case of heteroepitaxy in nonequilibrium conditions. Coalescence time and the corresponding diffusion coefficients at elevated temperatures were estimated for GaN and InN depositions. The rate of coalescence has been found to impact on the structure and morphology of III-nitride epilayers. A simple growth model was suggested to explain the formation of domain boundaries and (0001) stacking faults formed during the coalescence. In particular, it is shown that two adjacent and tilted, hexagonal-shaped 2H domains may form a noncoherent boundary explicitly along a {1100} plane. We also suggest that the interaction between tilted domains induces the localized lateral growth of the most epitaxially oriented domain forming a basal (0001) stacking fault followed by the formation of surface macrosteps, and consequently the termination of a threading dislocation by its dissociation and propagation under the formed (0001) stacking fault.