Nanowires are the building blocks for future optoelectronic devices at the nanoscale. The II-VI semiconductor ZnO is a promising material for ultraviolet optoelectronics, including light-emitting diodes (LEDs) and laser diodes (LDs). Electrically driven ZnO nanowire LEDs and LDs could serve as highly efficient nanoscopic light-sources, for example for optical data storage, imaging and chemical sensor applications. To grow a LED or LD structure, semiconducting materials with dominating negative (electrons) and positive (holes) charge carriers are required. Because ZnO is intrinsically n-type conducting, it is difficult to achieve p-type conducting ZnO as a thin-film or nanowire.
Pulsed-laser deposition (PLD) is a well established growth technique for high-quality oxide thin-films. In general it facilitates a nearly stoichiometric transfer of the chemical composition of source targets into the grown sample. Researchers at the University of Leipzig implemented a novel high-pressure PLD for growth of nanostructures. Using this new PLD process, phosphorus-doped ZnO nanowires were successfully grown. The dopant was added into the PLD source target in the form of P2O5. Optical spectroscopy of the band-edge-related light emission proved that stable acceptor levels with a binding energy of about 122 meV were induced homogenously in the ZnO:P nanowires. This is an important step towards p-type conducting ZnO nanowires as a necessary condition for future nano-optoelectronic devices based on p-n junctions. The results were published in Nanotechnology 45, 455707 (2007). Using electrical measurements, the p-type conductivity of P-doped wires has also been proven (unpublished).