p-Type ZnO materials: Theory, growth, properties and devices

Abstract In the past 10 years, ZnO as a semiconductor has attracted considerable attention due to its unique properties, such as high electron mobility, wide and direct band gap and large exciton binding energy. ZnO has been considered a promising material for optoelectronic device applications, and the fabrications of high quality p-type ZnO and p–n junction are the key steps to realize these applications. However, the reliable p-type doping of the material remains a major challenge because of the self-compensation from native donor defects (V O and Zn i ) and/or hydrogen incorporation. Considerable efforts have been made to obtain p-type ZnO by doping different elements with various techniques. Remarkable progresses have been achieved, both theoretically and experimentally. In this paper, we discuss p-type ZnO materials: theory, growth, properties and devices, comprehensively. We first discuss the native defects in ZnO. Among the native defects in ZnO, V Zn and O i act as acceptors. We then present the theory of p-type doping in ZnO, and summarize the growth techniques for p-type ZnO and the properties of p-type ZnO materials. Theoretically, the principles of selection of p-type dopant, codoping method and X Zn –2V Zn acceptor model are introduced. Experimentally, besides the intrinsic p-type ZnO grown at O-rich ambient, p-type ZnO (MgZnO) materials have been prepared by various techniques using Group-I, IV and V elements. We pay a special attention to the band gap of p-type ZnO by band-gap engineering and room temperature ferromagnetism observed in p-type ZnO. Finally, we summarize the devices based on p-type ZnO materials.

RaoP-Type ZnO Materials: Theory, Growth, Properties, and Devices

To develop an ultraefficient and reusable heterogeneous Fenton-like catalyst at a wide working pH range is a great challenge for its application in practical water treatment We report an oxygen vacancy promoted heterogeneous Fenton-like reaction mechanism and an unprecedented ofloxacin (OFX) degradation efficiency of Cu doped Fe3O4@FeOOH magnetic nanocomposite Without the aid of external energy, OFX was always completely removed within 30 min at pH 32–90 Compared with Fe3O4@FeOOH, the pseudo-first-order reaction constant was enhanced by 10 times due to Cu substitution (904/h vs 094/h) Based on the X-ray photoelectron spectroscopy (XPS), Raman analysis, and the investigation of H2O2 decomposition, •OH generation, pH effect on OFX removal and H2O2 utilization efficiency, the new formed oxygen vacancy from in situ Fe substitution by Cu rather than promoted Fe3+/Fe2+ cycle was responsible for the ultraefficiency of Cu doped Fe3O4@FeOOH at neutral and even alkaline pHs Moreover, the catalyst had an ex

Oxygen Vacancy Promoted Heterogeneous Fenton-like Degradation of Ofloxacin at pH 3.2-9.0 by Cu Substituted Magnetic Fe3O4@FeOOH Nanocomposite

The production of H2O2 has been taken for a crucial reason for antimicrobial activity of ZnO without light irradiation. However, how the H2O2 generates in ZnO suspension is not clear. In the presen...

Antimicrobial Mechanism Based on H2O2 Generation at Oxygen Vacancies in ZnO Crystals

Flowerlike CuO nanostructures were prepared by the coprecipitation method with postannealing in air at different temperatures. The results of X-ray diffraction and Raman and X-ray photoelectron spectroscopies show that the samples annealed at 400, 600, and 800 °C have a typical monoclinic structure and are absent of impurity phases. Magnetic measurements indicate that all of the CuO nanostructures show room-temperature ferromagnetism, whereas CuO bulk presents paramagnetism. The saturation magnetization of the samples was found to increase with increasing annealing temperature. The fitting results of the O 1s XPS spectra for the three samples indicate that oxygen vacancies exist in the samples and that the variation of the oxygen vacancy concentration is in complete agreement with the variation of the saturation magnetization. When the samples were annealed in oxygen atmosphere, the ferromagnetism of the samples decreased enormously. These results confirm that the observed room-temperature ferromagnetism ...

Room-Temperature Ferromagnetism of Flowerlike CuO Nanostructures

We investigated the electrical, magnetic, and magnetotransport properties of Li–Ni codoped ZnO thin films in the electron dominated, hole dominated, and insulating regimes. In a narrow window of oxygen growth pressure, 10−3–10−2 mbar, the films exhibited p-type conductivity with a maximum hole concentration ∼8.2×1017 cm−3. Magnetoresistance exhibited by the films is attributed to scattering of charge carriers due to localized magnetic moments. Insulating films showed superparamagnetic behavior, whereas both n-type and p-type films showed room temperature ferromagnetism. Our findings suggest that oxygen vacancies and Ni ions in cation site are jointly responsible for ferromagnetism that is not dependent on the carrier type.

S. Venkatesh

Papers

Oxygen vacancy controlled tunable magnetic and electrical transport properties of (Li, Ni)-codoped ZnO thin films