Ferromagnetism in Cu-doped polar and nonpolar GaN surfaces

We have performed density-functional calculations of energetic stability and electronic structure of copper (Cu) incorporation on polar GaN(0 0 0 1), nonpolar GaN( 1 1 2 ‾ 0 ) and GaN( 1 0 1 ‾ 0 ) surfaces. From surface energy calculations, it was found that the most stable positions of a Cu atom on the polar and nonpolar GaN surfaces are the Cu Ga incorporation on the first layer. Our surface energy results show that CuGa incorporation is energetically more favorable compared with CuN incorporation and Cu-interstitial sites. In addition, we have found that the magnetization in Cu-doped GaN( 1 1 2 ‾ 0 ) surface, ∼ 2.0 μ B /Cu atom, is stronger than in GaN(0 0 0 1) and ( 1 0 1 ‾ 0 ) surfaces, ∼ 0.3 μ B /Cu atom and ∼ 1.0 μ B /Cu atom, respectively. Our results are in good agreement with the available experimental data and provide a useful insight into the investigation of ferromagnetism in GaN-based diluted magnetic semiconductors.