The surface reconstructions and adatom kinetics on AlN(1102) and AlN(1101) surfaces in the presence of H2 molecules are investigated on the basis of density-functional theory calculations. Our surface phase diagram calculations demonstrate that the H-incorporated surfaces are invariably stable over the wide range of H2 pressure. We find that under the growth condition the adsorption energy of Al adatom on AlN(1102) surface is much larger than that on AlN(1101) surface. Furthermore, we find that the diffusion behavior of Al adatom on AlN(1101) surface is significantly influenced by the presence of hydrogen. These results suggest that impact of hydrogen ambient during the metal-organic vapor-phase epitaxy growth on AlN(1102) surface is quite different from that on AlN(1101) surface.

The reconstructions and adsorption behavior of Al atoms on semipolar AlN() surfaces under various growth conditions are investigated by first-principles pseudopotential calculations. Our calculations reveal that there are several reconstructions depending on the growth conditions: the surface with Al adatoms is stabilized under H-poor conditions while that with Al–H and N–H bonds is favorable under H-rich conditions. We also find that the adsorption of Al atoms strongly depends on the surface reconstruction. The adsorption of Al atoms on the reconstructed surface under H-poor conditions is found to be much easier than that under H-rich conditions. These results indicate that similarly to the case of a polar AlN(0001) surface the growth of AlN on a semipolar () surface during metal–organic vapor-phase epitaxy is prominent under H-poor conditions.

The crystal-structure deformation depending on lattice parameters in A N B 8−N compounds is investigated on the basis of density-functional theory (DFT) calculations. Our DFT calculations for C, BN and BeO demonstrate that the energy difference in cohesive energy along crystal structure deformation path strongly depends on the ionicity fi of materials. In particular, the energy barriers for structural deformation from threefold coordinated (hexagonal graphite) to fourfold coordinated (wurtzite) structures in BN and C are marked, whereas that in BeO is negligible. The difference in the energy barrier originates from both repulsive interaction among bond charges and attractive interaction among ionic charges. The repulsive interaction among bond charges in C (fi = 0) results in the highest energy barrier of 0.39 eV, while the attractive interaction among ionic charges in BeO with large ionicity (fi = 0.602) does in quite small energy barrier. These results imply that the ionicity is crucial for determining the energy change along crystal deformation path as well as the structural stability.

The initial growth processes on semipolar AlN surfaces, such as adsorption behavior of Al adatoms, are investigated on the basis of ab initio calculations and kinetic Monte Carlo (MC) simulations. By using surface phase diagrams, which are obtained by comparing the adsorption energy from ab initio calculations with gas-phase chemical potentials, we find that the adsorption of Al adatoms under H-poor condition is much easier than that under H-rich condition. Furthermore, our kinetic MC simulations demonstrate that the surface lifetime (diffusion length) of Al adatoms under H-poor condition is found to be four (two) orders of magnitude larger than that under H-rich condition. These differences implie that the growth under H-poor condition is much faster than that under H-rich condition, qualitatively consistent with the experimental results.

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