A growth diagram for plasma-assisted molecular beam epitaxy of In-face InN

Abstract

We investigated the role of temperature and In∕N flux ratios to determine suitable growth windows for the plasma-assisted molecular beam epitaxy of In-face (0001) InN. Under vacuum, InN starts decomposing at 435°C as defined by the release of N2 from the InN crystal and a buildup of an In adlayer and liquid In droplets on the sample surface. At temperatures greater than 470°C, InN decomposition was characterized by a release of both In vapor and N2 in the absence of a significant accumulation of an In adlayer. No growth was observed at substrate temperatures above 500°C or at temperatures in which the decomposition rates were higher than the growth rates. A growth diagram was then constructed consisting of two growth regimes: the “In-droplet regime” characterized by step-flow growth and relatively flat surfaces and the “N-rich regime” characterized by rough, three-dimensional surfaces. The growth diagram can then be used to predict the surface structure of films grown at varying substrate temperatures and In fluxes. A 2.5 monolayer In adlayer was observed during In-droplet growth, suggesting that an In wetting layer was necessary for step-flow growth.