The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. ...

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A comprehensive review of zno materials and devices

XPS and optical studies of different morphologies of ZnO nanostructures prepared by microwave methods

Magnesium-doped ZnO (ZMO) nanoparticles were synthesized through an oxalate coprecipitation method. Crystallization of ZMO upon thermal decomposition of the oxalate precursors was investigated using differential scanning calorimetry (DSC) and X-ray diffraction (XRD) techniques. XRD studies point toward a significant c-axis compression and reduced crystallite sizes for ZMO samples in contrast to undoped ZnO, which was further confirmed by HRSEM studies. X-ray photoelectron spectroscopy (XPS), UV/vis spectroscopy and photoluminescence (PL) spectroscopy were employed to establish the electronic and optical properties of these nanoparticles. (XPS) studies confirmed the substitution of Zn2+ by Mg2+, crystallization of MgO secondary phase, and increased Zn–O bond strengths in Mg-doped ZnO samples. Textural properties of these ZMO samples obtained at various calcination temperatures were superior in comparison to the undoped ZnO. In addition to this, ZMO samples exhibited a blue-shift in the near band edge photo...

Mg-Doped ZnO Nanoparticles for Efficient Sunlight-Driven Photocatalysis

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

Pure and Mg doped ZnO thin films were deposited at 400 °C on glass substrates by pulsed laser deposition. An x-ray diffractometer (XRD) was used to investigate the structural properties of the thin films. It is found that all the thin films have a preferred (002) orientation. The peak position of (002) orientation is found to shift from 34.39° to 34.55°. The lattice constants of ZnO thin films were also obtained from XRD data. It is found that, with the increase of the dopant concentration, the lattice constant a decreases from 3.25 to 3.23 A, and c decreases from 5.20 to 5.16 A. From the spectrophotometer transmittance data, the band gap energies of the thin films were calculated by a linear fitting process. The band gap energy of Mg doped ZnO thin film increases with increasing dopant concentration. In photoluminescence (PL) spectra, two PL emission peaks are found in pure ZnO thin films, one is the near band edge (NBE) emission at 3.28 eV, and the other is green-yellow-red emission at around 2.4 eV. However, with the increase of the dopants, no green-yellow-red emissions are found in PL of Mg doped ZnO thin films. The NBE emission has a blueshift compared with that of pure ZnO thin film (as much as 0.12 eV). As time goes on, NBE emission in pure ZnO thin film is enhanced, and the green-yellow-red emissions disappear.

B. I. Kim

Papers

Blueshift of near band edge emission in Mg doped ZnO thin films and aging