First-Principles Calculations of Solubilities and Doping Limits: Li, Na, and N in ZnSe

We present a comprehensive theoretical approach to determine concentrations of dopant impurities in semiconductors. The formalism is applied to the problem of acceptor doping in ZnSe. Formation energies and concentrations of impurities and native defects are expressed as a function of chemical potentials, for which experimentally accessible ranges are calculated. We show that limitations in the achievable hole concentrations can be explained by two mechanisms: one is the competition between various substitutional and interstitial configurations (compensation), the other is the solubility limit imposed by formation of other phases. Nitrogen is most promising among the dopants examined.