P-type ZnO is crucial for the realization of ZnO-based homojunction ultraviolet optoelectronic devices. The problem associated with the preparation of stable p-type ZnO with high hole density still hinders device applications. In this paper, we introduce an alternative route to stabilizing N in the oxidation process, the thermal stability of p-ZnO is significantly improved. Finally, we discuss the limitations of the alternative doping method and provide some prospective outlook of the method.

Semiconductor nanowires, with their unique capability to bridge the nanoscopic and macroscopic worlds, have been demonstrated to have potential applications in energy conversion, electronics, optoelectronics, and biosensing devices. One-dimensional (1D) ZnO nanostructures, with coupled semiconducting and piezoelectric properties, have been extensively investigated and widely used to fabricate nanoscale optoelectronic devices. In this article, we review recent developments in 1D ZnO nanostructure based photodetectors and device performance enhancement by strain engineering piezoelectric polarization and interface modulation. The emphasis is on a fundamental understanding of electrical and optical phenomena, interfacial and contact behaviors, and device characteristics. Finally, the prospects of 1D ZnO nanostructure devices and new challenges are proposed.

Flexible and transparent electronics enters into a new era of electronic technologies. Ubiquitous applications involve wearable electronics, biosensors, flexible transparent displays, radio-frequency identifications (RFIDs), etc. Zinc oxide (ZnO) and relevant materials are the most commonly used inorganic semiconductors in flexible and transparent devices, owing to their high electrical performances, together with low processing temperatures and good optical transparencies. In this paper, we review recent advances in flexible and transparent thin-film transistors (TFTs) based on ZnO and relevant materials. After a brief introduction, the main progress of the preparation of each component (substrate, electrodes, channel and dielectrics) is summarized and discussed. Then, the effect of mechanical bending on electrical performance is highlighted. Finally, we suggest the challenges and opportunities in future investigations.

The ultra-violet (UV) detection has a wide application in both civil and military fields. ZnO is recognized as one of ideal materials for fabricating the UV photodetectors due to its plenty of advantages, such as wide bandgap, low cost, being environment-friendly, high radiation hardness, etc. Moreover, the alloying of ZnO with MgO to make ZnMgO could continually increase the band gap from ~3.3 eV to ~7.8 eV, which allows both solar blind and visible blind UV radiation to be detected. As is well known, ZnO is stabilized in the wurtzite structure, while MgO is stabilized in the rock salt structure. As a result, with increasing the Mg content, the crystal structure of ZnMgO alloy will change from wurtzite structure to rock salt structure. Therefore, ZnMgO photodetectors can be divided into three types based on the structures of alloys, namely, wurtzite-phase, cubic-phase and mixed-phase devices. In this paper, we review recent development and make the prospect of three types of ZnMgO UV photodetectors.

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.

Deep-ultraviolet (DUV) light-emitting devices (LEDs) have a variety of potential applications. Zinc-oxide-based materials, which have wide bandgap and large exciton binding energy, have potential applications in high-performance DUV LEDs. To realize such optoelectronic devices, the modulation of the bandgap is required. This has been demonstrated by the developments of Mg_xZn_1-xO and Be_xZn_1-xO alloys for the larger bandgap materials. Many efforts have been made to obtain DUV LEDs, and promising successes have been achieved continuously. In this article, we review the recent progress of and problems encountered in the research of ZnO-based DUV LEDs.