Preparation and properties of ZnO and devices

ZnO has gained interest in part because of its large exciton binding energy (60 meV), good for lasing with low threshold. The renewed interest in ZnO is fuelled by availability of high quality substrates, reports of p-type conductivity, and ferromagnetic behavior when doped with transitions metals. The field is also fuelled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. Despite great strides there are still many challenges, the chief among them is the attainment of reproducibly low resistivity p-type ZnO. While ZnO already has many industrial applications owing to its piezoelectric properties and bandgap in the near UV, its applications to optoelectronic devices utilizing electrical injection has not yet been put to practice mainly due to the lack of p-type epitaxial layers. This review provides a discussion of some of the growth issues of ZnO-based epitaxial and heteroepitaxial layers and their use in a variety of devices. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.