Thermodynamic and electronic study of Ga 1 − x Mn xN films. A theoretical study

Abstract

Periodic slab calculations based on density functional theory were performed at the B3LYP level to gain insight into the surfaces of wurtzite GaN nanostructures. The (10 1 ¯ 0) and (11 2 ¯ 0) GaN surfaces are the most thermodynamically stable surfaces, the energy of the former being slightly smaller than that of the latter. The thermodynamic stability associated with the equilibrium shape of nanowires was determined using the calculated values. Doping with Mn further decreases the surface energy of (10 1 ¯ 0) and (11 2 ¯ 0). The minimum surface energy of Ga 1 − x Mn xN (0.04 ≤ x ≤ 0.17) is found at x ~ 0.08, for (10 1 ¯ 0) and (11 2 ¯ 0) slab models. Substitution of Ga with Mn in different positions relative to the surface shows that the total energy increases as the Mn atoms move from the surface layer to the interior sites of the slabs. Mn doping is also responsible for decreases in the band gap energy: the minimum calculated band gap in the Ga 1 − x Mn xN (10 1 ¯ 0) slab was found at x ~ 0.17, whereas the (11 2 ¯ 0) surface presented the corresponding minimum at x ~ 0.04. The magnetic moments associated with Mn were observed to increase as the ion positions moved closer to the surfaces.