Identification of a Deep Acceptor Level in ZnO Due to Silver Doping

There remains considerable interest in the behavior of acceptors in ZnO, the ultimate goal being the realization of device grade p-type material. Silver is a candidate acceptor, and, in this study, in situ doping of silver was performed during plasma-assisted molecular beam epitaxy. Silver concentrations, as determined by ion beam analysis, ranged between 10(18) cm(-3)and 10(20) cm(-3), with as much as 94% incorporated substitutionally on Zn lattice sites. Variable magnetic field Hall effect measurements detected no evidence of holes, and 4 K photoluminescence was dominated by donor bound excitons. Transient capacitance measurements, however, suggested that incorporated silver had led to the formation of an acceptor, located approximately 320 meV above the valence band edge, indicating that compensation remains a significant issue in determining the conductivity of ZnO.