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

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 degrees C as defined by the release of N-2 from the InN crystal and a buildup of an In adlayer and liquid In droplets on the sample surface. At temperatures greater than 470 degrees C, InN decomposition was characterized by a release of both In vapor and N-2 in the absence of a significant accumulation of an In adlayer. No growth was observed at substrate temperatures above 500 degrees 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.