P-Type Phosphorus Doped ZnO Wires for Optoelectronic Applications

Semiconductor nanowires are especially attractive building blocks for assembling active and integrated nanosystems since the individual nanostructures can function as both device elements and interconnects. Among wide band gap II-VI semiconductors, ZnO seems to be one of the most promising materials for optoelectronic applications. This is due to its stable excitons, having a large binding energy of 60 meV [Ellmer et al., 2008, Jagadish & Pearton, 2006], which is important for applications of UV light-emitting devices and laser diodes with high efficiency. Therefore, growth of p-type conductive ZnO material is a prerequisite step since ZnO is intrinsically n-type [Look et al., 2001]. The growth of semiconductor nanowires with reproducible electronic properties, including the controlled incorporation of n-type and/or p-type dopants, has been realized in silicon, indium phosphide, and gallium nitride [Lieber & Wang, 2007]. In comparison with the semiconductors mentioned above, doping of ZnO seems more difficult not only for wires but films and bulk crystals due to the low dopant solubility and the self-compensation effect of intrinsic defects [Park et al., 2002]. It is also desired to more deeply understand the underlying doping physics [Zhang et al., 2001] for the achievement of a high-quality compound-semiconductor p-n junction. Until now, there are only few reports on doped ZnO nanowires for p-type conductivity, possibly due to the obvious difficulties in both growth and optical/electrical characterization. Liu et al. [2003] prepared boron-doped ZnO nanowires and ZnO:B/ZnO nanowire junction arrays by a two-step vapor transport method in pores of anodic aluminum oxide membrane. A p-n junction-like rectifying behavior was observed. Lin et al. [2005] also reported a p-n rectification behavior of nitrogen doped ZnO (ZnO:N) nanowires/ZnO film homojunctions, where the ZnO:N nanowires were prepared by a post-growth NH