Theory of Ga, N and H terminated GaN (0001)/(000 1 ) surfaces

We present a theoretical study of atomic structures, electrical properties and formation energies for a variety of possible reconstructions with 1×1 and 2×2 periodicity of the GaN(0001) and (000 1 ) surfaces. We find that during MBE growth in the (0001) direction 2×2 structures become stable under N rich growth conditions while Ga rich environment should yield structures with 1×1 periodicity. Considering MBE growth on (000 1 ) surfaces, among the investigated structures only those with 1×1 periodicity are predicted to be stable. During MOCVD growth, where H terminated surfaces may occur, only structures with lx1 periodicity are found to be stable for both growth directions.