The electrical activity of GaN doped with transition metal impurities

The electronic properties of GaN doped with three transition metal impuriti es (titanium, nickel and gold) have been calculated using a density functio nal approach. Both substitutional and interstitial mechanisms for dopant in corporation have been considered, together with the effect of varying the c harge state of the impurity. The electrical activity of the metal impuritie s is characterized by considering the defect levels in the band gap, the Mu lliken charges on the atoms and the local distribution of valence charge de nsity. The calculated formation energies indicate that a substitutional mec hanism is preferred and that all three metals act as donor dopants.