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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 acceptorlike 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.
Zinc oxide (ZnO) is a compound semiconductor with a direct band gap and high exciton binding energy. The unique property, ie, high efficient light emission at ultraviolet band, makes ZnO potentially applied to the short-wavelength light emitting devices. Powered, 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. Negative defects in ZnO can be divided into donor-like and acceptorlike ones. The self-compensation has been found mainly to originate from zinc interstitial and oxygen vacancy related donors. Whilst 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. Although some novel ideas have been extens ively 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 verified successfully.In this article, 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.