Heteroepitaxial evolution of AlN on GaN Grown by metal-organic chemical vapor deposition

We have investigated the morphological evolution during heteroepitaxial growth of AlN on GaN by metal-organic chemical vapor deposition at different V/III ratios. Two-dimensional layer-by-layer and step flow growth modes, combined with strain-induced cracking, are observed at low and intermediate V/III ratios, while nitrogen-rich conditions yield three-dimensional domain-like growth due to limited Al adatom diffusion. Samples grown at the metal-rich conditions exhibit a crosshatch pattern of surface undulations possibly related to the presence of misfit dislocations that form at the early stages of nucleation. Our observations show that the local stoichiometry at the vapor-solid interface strongly influences the adatom kinetics during the growth, thereby affecting the nature of strain relaxation and growth mode. (C) 2004 American Institute of Physics.