Interface formation of scandium nitride on the GaN(0001) surface: A first-principles study

Self-consistent periodic density functional theory calculations are used to investigate the role of scandium (Sc) impurity atoms during GaN growth. Adsorption and diffusion of Sc atoms on GaN(0001)-2 x 2 surface is examined and it is shown that Sc atoms preferentially adsorb at the T-4 sites at low and high coverages (from 1/4 up to 1 monolayer). It is also found that N atoms are relatively immobile compared to Ga as well as Sc atoms on the GaN(0001) surface. In addition, calculating the relative surface energy of several configurations and various Sc concentrations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Sc and Ga chemical potentials. Based on these results, we have found that incorporation of Sc adatoms in the Ga-substitutional site is energetically more favorable compared with the adsorption on the top layers. This effect leads to the formation of an interfacial crystalline ScN layer on the GaN(0001) surface, which can offer a good interfacial combination between Sc and GaN substrate. Our calculations show that the scandium incorporation is most favorable under a nitrogen environment, in agreement with experimental results. (C) 2013 Elsevier B. V. All rights reserved.