Laser-ablation CVD Growth And Device Application Of Acceptor-doped ZnO Nanowires

Zinc oxide (ZnO) is an important II-IV oxide compound semiconductor with a directband gap of3.37eV, and a relatively high exciton bound energy of60meV, which is higherthan the room-temperature thermal energy (26meV). So excitons counld exist stably at roomtemperature. Based on the above characteristics, ZnO is widely used as trasprent conductiveoxide electrodes now and could be expected for application as semiconductor lasers, UVlight-emitting diodes, and UV detectors.It seems to be difficult to generate p-type doping impurities in ZnO, due to the lowdopant solubility and self-compensation effect of intrinsic defects, which hinders itsapplication in the field of optoelectronics. In recent years, p-type doping has made greatprogress. Many efforts on the growth of p-type ZnO by doping group V elements as p-typedopants were reported. In contrast, there have been only a few reports on group I elements,especially for sodium. This thesis mainly focuses on the growth of sodium and phosphorusacceptor-doped nanowires by a laser ablation vapor depositionand their deviceapplications.The main resuts are as follows:1. Growth of acceptor-doped ZnO nanowires by laser ablation chemical vapor deposition(LACVD). P2O5and Na2CO3were used as the acceptor dopants by doping target in this paperand high purity N2gas was as carrier gas to grow doped ZnO nanowires. Also, we studied theinfluence of the growth parameters on the morphology and microstructure of the dopednanowires, such as substrate temperature, growth pressure, and the thickness of gold catalystlayer. The optimal experimental parameters for the growth of doped nanowires were obtained.2. Optical properties of the acceptor-doped ZnO nanowires. By measuring thephotoluminescence (PL) spectra of the intrinsic and acceptor-doped ZnO nanowires at roomtemperature, we studied the influence of dopants on the relative intensity of intrinsic UV andvisible defect emissions. PL fine structure of intrinsic excitons and acceptor-related peaks forzinc oxide nanowires were obtained at low temperature e.g.15K. These characteristicemission peaks, as optical fingerprint, were ascribed to the sodium or phosphorus relatedacceptors in ZnO. By measuring the temperature-dependent PL spectra, we discussed the PL dynatics behavior of different emission peaks. Therefore, the acceptor ionization energy wascalculated and the possible defect states of different acceptors were proposed.3. Febrication of ZnO nanowire/film PN homojunction diodes. The low-pressure PLDmethod was used to grow a layer of n-type alumiun doped ZnO (AZO). Then LACVDmethod was used to grow acceptor-doped (ZnO:P, ZnO:Na) ZnO nanowire arrays on AZOthin films and a ZnO nanowire/film homojunction were febricated. The corresponding I-Vcurve measurements exhibit a clear rectifying behavior of PN diode.