Abstract
The difficulties in the p-type doping of ZnS and the n-type doping of ZnTe are well known phenomena in the II-VI semiconductor community. We find extremely strong evidence from the results of parameter-free first-principles calculations that the major source of doping difficulties in II-VI semiconductors is the formation of self-compensating centers resulting from bond rearrangement at dopants. The most important self-compensating center is identified. When the formation energy of this center is endothermic, there is no problem with doping but when it is exothermic, low resistance doping is not possible. The theoretical results on formation energies and dopability are in excellent accord with experimental data.