Bound states of the Fe impurity in wurtzite GaN from hybrid density-functional calculations

We analyze the energetics and localization of the charged states of Ga-substituting Fe in wurtzite GaN via hybrid-density-functional calculations and a Bader analysis of charge and magnetization. Fe exhibits an unusual bound-hole q = +1 charge state in addition to q = 0, -1 charge states, with thermal levels epsilon(+/0) and epsilon(0/-) at 0.3 and 2.4 eV above the valence band. Electron and hole bound to Fe are localized gap states unsuitable for carrier-mediated magnetic order. The effective valence charges of the charged states compared to the neutral case suggest that Fe approximately follows the charge self-regulation rule.