It was recalled that wide-bandgap semiconductors could be easily doped either n-type or p-type, but not the other, so that it was relatively easy to make n-type ZnSe but difficult to make p-type ZnSe. Compensation by native point defects was the usual explanation for such doping problems. Here, the concentrations of all of the native point defects in ZnSe were determined by using ab initio total energy calculations. It was found that native defect concentrations were too low to cause compensation in stoichiometric ZnSe. Small deviations from stoichiometry could produce enough native defects to compensate doping. However, in Zn-rich or Se-rich material, native defects could compensate both n-type and p-type doping. Therefore, deviations from stoichiometry could not explain why ZnSe preferred to be n-type. In the case of Li-doped ZnSe, it was shown that the true cause of the doping difficulties was two-fold. One factor was the tendency of Li to become an interstitial donor, and the other factor was the limited solubility of the dopant.
D.B.Laks, C.G.Van de Walle, G.F.Neumark, S.T.Pantelides: Materials Science Forum, 1992, 83-87, 1225-34