Microscopic mechanism of the wurtzite-to-rocksalt phase transition of the group-III nitrides from first principles

Abstract

There are mainly two kinds of microscopic mechanisms previously proposed for the structural phase transition from wurtzite to rocksalt, that is, the ``hexagonal'' and ``tetragonal'' paths. The present work gives a comparative study of these two mechanisms in group-III nitrides (AlN, GaN, and InN) from the energetic point of view based on first-principles calculations. The calculated results indicate that the energy-favored mechanism is dependent not only on the internal compositions but also on the external pressures. AlN and GaN prefer the hexagonal and the tetragonal paths, respectively, in a large pressure range investigated; however, in the case of InN, the tetragonal path is favored under lower pressure but the hexagonal one under higher pressure. In addition, a real-time measurement of the radial distribution function or the axial ratio $c∕a$ is suggested to distinguish these two transition paths in experiment. We also propose a simple model to make a rough estimate of the hysteresis cycle of the wurtzite-rocksalt transition and obtain good agreement with the experimental results for AlN and InN.