A theoretical study of O chemisorption on GaN (0001)/(0001) surfaces

We present a theoretical study of atomic structures and formation energies for a variety of possible oxygen induced reconstructions at the GaN (0 0 0 1) and (0 0 0 1̄) surfaces. We find that at the nominally Ga terminated (0 0 0 1) surface a coverage of ΘO=0.375 ML on top of the ideal surface is stable. Only in a very oxygen rich environment a full monolayer of O can be adsorbed at the ideal surface. On top of the Ga atop structure at the (0 0 0 1) surface, which consists of a Ga layer on top of the ideal surface, a full monolayer of oxygen is stable. At the nominally N terminated (0 0 0 1̄) surface which is usually found to exhibit the Ga atop reconstruction the most stable surfaces have oxygen coverages of ΘO=0.75 ML and ΘO=1.0 ML depending on the oxygen chemical potential. In all stable structures O is exclusively bound to Ga.