Density functional calculations of the strain effects on binding energies and adatom diffusion on (0 0 0 1) GaN surfaces

Density functional calculations were carried out to study the binding energies and diffusion barriers for adatoms on GaN surfaces. The binding energies and diffusion barriers were calculated for Ga and N adatoms on both Ga terminated and N terminated (0 0 0 1) surfaces, subjected to a hydrostatic compressive and tensile strain in the range of 0–5%. An understanding of the changes in adatom binding and diffusion under differing growth conditions was obtained. For example, the diffusion barrier of a Ga adatom is maximum for a 1% compressive strain and decreases rapidly at higher strains whereas the diffusion barrier for a N adatom is lowest at a 1% tensile strain and increases as the strain increases on a N terminated surface. These changes can explain differences in optimal growth conditions on bulk III-Nitride substrates as opposed to on III-Nitride template layers grown on foreign substrates.