Semiconductor nanostructures have attracted much attention as promising candidates for future electro-optical devices. In nanostructures, the carrier-state density is concentrated in discrete energy levels, which enables the enhancement of exciton oscillator strength and light-emitting efficiency. As a result, the performance of nanostructure-based optical devices is expected to be improved and be less temperature dependent.[1]Among the wide variety of semiconductor nanostructures, ZnO nanostructures, as wide bandgap semiconductors, are even more attractive for high-efficiency short-wavelength optoelectronic nanodevices, [2±4] due to their large excitonic binding energy (»60 meV) and high mechanical and thermal stabilities. For one-dimensional ZnO nanostructures, different shape structures, such as tetrapod nanorods, [5,6] nanowires, [7,8]

Well-aligned ZnO nanowire (NW) arrays with durable and reproducible p-type conductivity were synthesized on alpha-sapphire substrates by using N2O as a dopant source via vapor-liquid-solid growth. The nitrogen-doped ZnO NWs are single-crystalline and grown predominantly along the [110] direction, in contrast to the [001] direction of undoped ZnO NWs. Electrical transport measurements reveal that the nondoped ZnO NWs exhibit n-type conductivity, whereas the nitrogen-doped ZnO NWs show compensated highly resistive n-type and finally p-type conductivity upon increasing N2O ratio in the reaction atmosphere. The electrical properties of p-type ZnO NWs are stable and reproducible with a hole concentration of (1-2) x 10(18) cm(-3) and a field-effect mobility of 10-17 cm2 V(-2) s(-1). Surface adsorptions have a significant effect on the transport properties of NWs. Temperature-dependent PL spectra of N-doped ZnO NWs show acceptor-bound-exciton emission, which corroborates the p-type conductivity. The realization of p-type ZnO NWs with durable and controlled transport properties is important for fabrication of nanoscale electronic and optoelectronic devices.