Vanadium adsorption and incorporation at the GaN(0001) surface: A first-principles study

We have carried out first-principles spin-polarized calculations in order to study the energetics and electronic structure of vanadium adsorption and incorporation on GaN(0001)-2 x 2 surface using density-functional theory within a plane-wave ultrasoft pseudopotential scheme. It was found that V atoms preferentially adsorb at the T4 sites at low and high coverages (from 1/4 up to 1 monolayer). In addition, calculating the relative surface energy of several configurations and various V concentrations, we constructed a phase diagram showing the energetically most stable surfaces as a function of the Ga chemical potential. Based on these results, we found that incorporation of V adatoms in the Ga-substitutional site is energetically more favorable compared with the adsorption on the top layers. Our calculations show that the vanadium incorporation is most favorable under a nitrogen environment, in agreement with recent experimental results.