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(0001), nonpolar GaN(11 (2) over bar0) and GaN(10 (1) over bar0) 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 Cu-Ga incorporation is energetically more favorable compared with Cu-N incorporation and Cu-interstitial sites. In addition, we have found that the magnetization in Cu-doped GaN(11 (2) over bar0) surface, similar to 2.0 mu(B)/Cu atom, is stronger than in GaN(0001) and (10 (1) over bar0) surfaces, similar to 0.3 mu B/Cu atom and similar to 1.0 mu 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. (C) 2013 Elsevier B. V. All rights reserved.