Ab initio-based bulk and surface thermodynamics of InGaN alloys: Investigating the effects of strain and surface polarity

The growth of high In content InGaN with sufficiently high crystal quality is challenging due to the differences in the GaN and InN thermodynamics. The surprisingly different thermodynamics is due to a complex competition between strain and chemistry and mediated by the different indium and gallium atomic radii as well as their different bonding enthalpies with nitrogen. In the present work, we investigate bulk and surface thermodynamics of molecular beam epitaxial (MBE) growth of InxGa1-xN for the technologically relevant (0001) and (000 (1) over bar) growth planes by means of density functional theory calculations. Our calculations confirm that coherent growth fully suppresses phase separation through spinodal decomposition. However, the biaxial strain is found to have a marginal effect on the critical temperatures for InxGa1-xN decomposition. Furthermore, the thermal stability of excess indium is found to be remarkably higher on N-polar surfaces than on the Ga-polar surfaces. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim