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

With large surface-to-volume ratios and Debye length comparable to their small sizes, one-dimensional inorganic nanostructures have extensively been investigated and widely used to fabricate high-performance nanoscale electronic and optoelectronic devices. This feature article reviews the state-of-the-art research activities that focus on the one-dimensional inorganic nanostructures and their photodetector applications. It begins with a survey of one-dimensional inorganic nanostructures and the fundamentals of photodetectors. Some remarkable photoresponse characteristics are then presented, which are organized into sections covering several kinds of important nanostructures, such as ZnO, V 2 O 5 , ZnS, In 2 Se 3 , InSe, CdS, CdSe, ZnSe, Sb 2 Se 3 , ZrS 2 , Ag 2 S, and Zn x Cd 1-x Se. Each section describes the corresponding photodetective properties in detail. Finally, the article concludes with some perspectives and outlook on the future developments in the field.

Recent Developments in One-Dimensional Inorganic Nanostructures for Photodetectors

Recent advances in ultraviolet photodetectors

With large surface-to-volume ratios and Debye length comparable to their small sizes, one-dimensional inorganic nanostructures have extensively been investigated and widely used to fabricate high-performance nanoscale electronic and optoelectronic devices This feature article reviews the state-of-the-art research activities that focus on the one-dimensional inorganic nanostructures and their photodetector applications It begins with a survey of one-dimensional inorganic nanostructures and the fundamentals of photodetectors Some remarkable photoresponse characteristics are then presented, which are organized into sections covering several kinds of important nanostructures, such as ZnO, V 2 O 5 , ZnS, In 2 Se 3 , InSe, CdS, CdSe, ZnSe, Sb 2 Se 3 , ZrS 2 , Ag 2 S, and Zn x Cd 1-x Se Each section describes the corresponding photodetective properties in detail Finally, the article concludes with some perspectives and outlook on the future developments in the field

We demonstrated a simple and low-cost fabrication of ZnO p-n homojunction. The junction consists of n-type ZnO nanowires array by a hydrothermal method covered with p-type Al, N co-doped ZnO film by a sol-gel method. The junction exhibits good rectification characteristics, with reverse leakage current and rectification ratio of ∼5 μA and ∼150 at bias of 3 V, respectively. The junction is operated as a photodetector when light radiation is shined on the glass-side of the device. The photodetector shows a peak responsivity at 384 nm with UV-visible responsivity ratio (R384 nm/R550 nm) of ∼70 at an operating bias of −3 V.

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C. H. A. Tsang

Papers

ZnO nanowires array p-n homojunction and its application as a visible-blind ultraviolet photodetector