Recent progress of the native defects and p-type doping of zinc oxide

Zinc oxide (ZnO) is a compound semiconductor with a direct band gap and high exciton binding energy. The unique property, i.e., high efficient light emission at ultraviolet band, makes ZnO potentially applied to the short-wavelength light emitting devices. However, efficient p-type doping is extremely hard for ZnO. Due to the wide band gap and low valence band energy, the self-compensation from donors and high ionization energy of acceptors are the two main problems hindering the enhancement of free hole concentration. Native defects in ZnO can be divided into donor-like and acceptor-like ones. The self-compensation has been found mainly to originate from zinc interstitial and oxygen vacancy related donors. While the acceptor-like defect, zinc vacancy, is thought to be linked to complex shallow acceptors in group-VA doped ZnO. Therefore, the understanding of the behaviors of the native defects is critical to the realization of high-efficient p-type conduction. Meanwhile, some novel ideas have been extensively proposed, like double-acceptor co-doping, acceptor doping in iso-valent element alloyed ZnO, etc., and have opened new directions for p-type doping. Some of the approaches have been positively judged. In this article, we thus review the recent (2011–now) research progress of the native defects and p-type doping approaches globally. We hope to provide a comprehensive overview and describe a complete picture of the research status of the p-type doping in ZnO for the reference of the researchers in a similar area.