First-principles spin-polarized calculations were used to study the adsorption and diffusion of 3d transition metal (Ti, V, Cr, Mn, Fe, Co and Ni) atoms on a GaN(00•1)-(2 x 2) surface using density functional theory within a plane-wave ultra-soft pseudopotential scheme. The results showed that, for Ti, V, Cr and Mn atoms, the most stable adsorption sites were all at the T4 site (the top site of the N-surface atom), whereas Fe, Co and Ni slightly preferred the H3 hollow site. The adsorption energies could vary significantly with different TM atoms. A comparative study suggested that the TM-N bond formation was energetically more favourable for Ti, V and Cr atoms, while the formation of a TM-Ga surface alloy was more favourable for elements such as Fe, Co and Ni, as experimental results had shown. It was found that the 3d TM adatom diffusion energy barrier between the H3 and T4 sites was around 0.40eV, which was an indication of a significant TM adatom diffusion on the GaN(00•1) surface. Furthermore, the total magnetic moment increased for Ti, V, Cr and Mn adsorbates successively and then decreased for Fe, Co and Ni adsorbates. The density of states indicated that the adsorption of Ti, V and Cr atoms results in semiconductor behaviour, while the adsorption of Mn, Fe and Co atoms presented a half-metallic character. These properties made the TM/GaN systems promising for yielding high-efficiency metal-semiconductor spin injection devices.

Adsorption and Diffusion of 3d Transition Metal Atoms on the GaN(0001) Surface. R.González-Hernández, W.López-Pérez, M.G.Moreno-Armenta, J.A.Rodríguez: Journal of Applied Physics, 2011, 110[8], 083712