Stability of the cubic phase in GaN doped with 3d-transition metal ions

We investigate the stability of the zinc-blende (ZB) phase in GaN doped with transition metal ions using generalized-gradient approximation (GGA) calculations. The GGA calculations show that the ZB phase can be stabilized when the concentrations of the Cr and Mn ions are greater than 21% and 27% in GaCrN and GaMnN alloys, respectively. In GaFeN alloys, the stabilization of the ZB phase occurs at a much higher concentration of the Fe ions. If strong on-site Coulomb repulsion (U) is included, the ZB phase cannot be stabilized for all Fe concentrations. We also study the effects of electron and hole doping on the stability of the ZB phase in GaMnN alloys, and find that the critical concentration is reduced to 13% by doping one electron per Mn ion, while hole doping with a hole per Mn ion does not much affect the critical concentration.