Several hundred thousands of tons of ZnO are used by per year, e.g. as an additive to concrete or to rubber. In the field of optoelectronics, ZnO holds promises as a material for a blue/UV optoelectronics, alternatively to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits, which are transparent in the visible or for semiconductor spintronics. The main problem is presently, however, a high, reproducible and stable p-doping. We review in this contribution partly critically the material growth, fundamental properties of ZnO and of ZnO-based nanostructures, doping as well as present and future applications, with emphasis on the electronic and optical properties including stimulated emission. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

ZnO : From basics towards applications

ZnO is presently experiencing a research boom with more than 2000 ZnO-related publications in 2005. This phenomenon is triggered, for example, by hope to use ZnO as a material for blue/UV optoelectronics as an alternative to GaN, as a cheap, transparent, conducting oxide, as a material for electronic circuits that are transparent in the visible or for semiconductor spintronics. Currently, however, the main problem is to achieve high, reproducible and stable p-doping. Herein, we critically review aspects of the material growth, fundamental properties of ZnO and ZnO-based nanostructures and doping as well as present and future applications with emphasis on the electronic and optical properties including stimulated emission.

ZnO: Material, Physics and Applications

In this work we present a detailed Raman scattering investigation of zinc oxide and aluminum-doped zinc oxide (AZO) films characterized by a variety of nanoscale structures and morphologies and synthesized by pulsed laser deposition under different oxygen pressure conditions. The comparison of Raman spectra for pure ZnO and AZO films with similar morphology at the nano/mesoscale allows to investigate the relation between Raman features (peak or band positions, width, relative intensity) and material properties such as local structural order, stoichiometry, and doping. Moreover Raman measurements with three different excitation lines (532, 457, and 325 nm) point out a strong correlation between vibrational and electronic properties. This observation confirms the relevance of a multi-wavelength Raman investigation to obtain a complete structural characterization of advanced doped oxide materials.

Multi-wavelength Raman scattering of nanostructured Al-doped zinc oxide

We report on the occurrence of high temperature ferromagnetism (FM) in ZnO nanoparticles (NPs) doped with Co-atoms. ZnO NPs of two different initial sizes are doped with 3% and 5% Co using ball milling and FM is studied at room temperature and above. X-ray diffraction and high-resolution transmission electron microscopy analysis confirm the absence of metallic Co clusters or any other phase different from wurtzite-type ZnO. UV-visible absorption studies show change in band structure and photoluminescence studies show green emission band at 520 nm indicating incorporation of Co-atoms and presence of oxygen vacancy defects, respectively in ZnO lattice. Micro-Raman studies of doped samples shows defect related additional bands at 547 and 574 cm−1. XRD and Raman spectra provide clear evidence for strain in the doped ZnO NPs. The field dependence of magnetization (M-H curve) measured at room temperature exhibits the clear FM with saturation magnetization (Ms) and coercive field (Hc) of the order of 3–7 emu/g a...

High temperature ferromagnetism and optical properties of Co doped ZnO nanoparticles

Herein, we report the optical and magnetic properties of Mn- and Co-doped ZnO nanorods fabricated via a simple one-step aqueous-based chemical method. Interestingly, SEM results reveal a uniform size distribution of the nanorods throughout the substrate. The UV emission band of doped ZnO nanorods reveals a red shift from 382 to 384.5 nm, indicating a band-edge bending due to the dopants. The defect-related band centered at 600 nm is suppressed (ID/IUV = 1−0.35) considerably in doped nanorods, revealing the quenching of surface defects present in the nanostructures. XRD, XPS, Raman spectra, and EDS data demonstrate a successful incorporation of TM dopants in ZnO nanorods. Localized SAED patterns taken using nanoprobe size reveals that the nanorods are single crystals, grown along the c-axis [0002] direction. A systematic evalution of the enhancement in ferromagnetism (M = 0.15 × 10−2 to 1.3 × 10−2 emu/g) is found in modified doped ZnO nanorods.

Aqueous Synthesis of Mn- and Co-Doped ZnO Nanorods

Raman scattering has been used to study the influence of manganese, an effective dopant to obtain ZnO diluted magnetic semiconductors, on the lattice dynamics of ZnO. It is found that Mn doping increases the lattice defects and induces two Raman vibration modes of 275 and 526cm−1. On the other hand, high temperature (TC higher than 350K) ferromagnetism is observed in Zn1−xMnxO (x⩽0.02) nanoparticles. It is found that the ferromagnetism of Zn1−xMnxO nanoparticles is strongly related to defects in ZnO.

Raman scattering and high temperature ferromagnetism of Mn-doped ZnO nanoparticles

Mn-doped ZnO nanorods are prepared by a chemical vapor deposition method using zinc and MnO2 powders as source materials of Zn and Mn, respectively. Cathodoluminescence (CL) characterization indicates that the Mn-doped ZnO nanorods grown at different growth temperatures have different oxygen vacancy concentrations. Room temperature ferromagnetism with a saturation magnetization of 0.87μB∕Mn has been observed in Mn-doped ZnO nanorods grown at 650°C, in which moderate oxygen vacancy concentration is observed by CL characterization. It is also found that oxygen vacancies play an important role in the appearance of room temperature ferromagnetism in Mn-doped ZnO nanorods.

G. J. Huang

Papers

Raman scattering and high temperature ferromagnetism of Mn-doped ZnO nanoparticles

Cathodoluminescence and room temperature ferromagnetism of Mn-doped ZnO nanorod arrays grown by chemical vapor deposition

Erratum: “Raman scattering and high temperature ferromagnetism of Mn-doped ZnO nanoparticles” [Appl. Phys. Lett. 88, 252502 (2006)]