Control of doping by impurity Cchemical potentials: predictions for p-type ZnO.

Theoretical work has so far focused on the role of host-element chemical potentials in determining defect formation energies that control doping levels in semiconductors. Here, we report on our analysis of the role of the dopant-impurity chemical potential, which depends on the source gas. We present first-principles total-energy calculations that demonstrate a wide variation in the possible effective chemical potential of N. We account in detail for the recent puzzling observations of doping ZnO using N2 and N2O and predict that the use of dilute NO or NO2 gas would resolve the long-standing problem of achieving p-type ZnO.