Energetics of oxygen adsorption and incorporation at InN polar surface: A first-principles study

First principles calculations are performed to study the adsorption and incorporation of oxygen at InN polar surfaces as a function of oxygen coverage. We find that the adsorption of oxygen at InN surfaces is higher on the N-polar than on In-polar. The calculations show that for the low coverage regime (x ≤ 0.5 ML) both orientations are active towards the adsorption of oxygen; this implies that the reaction between the O atoms and the surface is strongly exothermic. As the coverage of O exceeds 0.5 ML a large difference in adsorption energies, of almost 2.5 eV, is observed between (0001) and (000$ \bar 1 $) surfaces indicating that the (000$ \bar 1 $) surface is more active towards oxygen adsorption than the (0001) surface. The high coverage of oxygen changes the surface structure of InN due to the difference in binding energy (O-In bonds are stronger than In-N ones). This result shows explicitly that the formation of In adlayer is disturbed by the O adsorption. Concerning the energetics of O incorporation our results show that it is more favourable for O to substitute a N atom in one of the top layers near the surface than in bulk, indicating that there is a strong tendency for O to reside at the surface rather than in subsurface layers.