Mechanism and kinetics of early growth stages of a GaN film

Abstract

The growth of GaN islands on the substrate surface covered with an AlN buffer layer is theoretically investigated at the stages of nucleation and Ostwald ripening in the temperature range 480–1000°C. The following inferences are made from analyzing the results obtained. (1) At temperatures T>650°C, the growth of islands is controlled by the chemical reaction of formation of GaN molecules around the periphery of the island surface. Islands nucleated at these temperatures are characterized by a large spread in their sizes. (2) At temperatures T<600°C, the island growth is governed by the surface diffusion of nitrogen atoms. Islands nucleated at these temperatures are virtually identical in size. (3) In the temperature range 600–650°C, the mechanism of island growth gradually changes over from the mechanism associated with the surface diffusion of nitrogen atoms with a large mean free path to the mechanism determined by the diffusion of gallium atoms with a smaller mean free path. The supersaturation, flux, and size distribution functions of GaN nuclei are calculated at different substrate temperatures. The phase diagrams describing the evolution in the phase composition of GaN islands with variations in temperature are constructed.