Controllable Growth Of Vertically Aligned ZnO Nanorod Arrays By Solution Method And The Electrical Mechanism Of N-doped ZnO Thin Films

As anⅡ-VI group semiconductor, ZnO has attracted great interest for its wide band gap (3.37eV) and relatively large exciton binding energy (60meV) at room temperature (RT). It has been regarded as one of the most promising candidates for the next generation of ultraviolet (UV) light-emitting diode (LED) and lasing diode (LD) operating at high temperatures and in harsh environments.One-dimensional (1D) nanostructure materials have been extensively studied because of their potential applications in nanoelectronic devices, such as field-effect transistors, single-electron transistors, photodiodes, and chemical sensors. ZnO has probably the richest family of nanostructures among all materials, which exhibit the most splendid and abundant configurations of nanostructures that one material can form. Up to now, numerous experimental attempts have been reported to fabricate ZnO nanorod materials, such as molecular beam epitaxy (MBE), pulsed laser deposition (PLD), sputtering, electrochemical deposition, vapor phase transport (VPT), chemical vapor deposition (CVD), thermal evaporation. Compared with the methods mentioned above, the wet chemical base deposition (CBD) method as a high performance growth technique for ZnO nanorod/nanowire is especially attractive due to its obvious advantages of low-cost, low temperature operation and environmental friendliness. ZnO nanorods are studied by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence spectra (PL), and Raman scattering spectra.In addition, for the application of ZnO based optoelectronic devices, realization of stable and reproducible p-type ZnO has long been the bottle-neck of ZnO-base optoelectronic devices. Nitrogen has been theoretically predicted to be the most promising candidate for producing a shallow acceptor level in ZnO compared with other potential elements, because it has almost the same ionic radii as that of O for ZnO.In this paper, N-doped ZnO films are studied using Hall effect measurements, X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption near-edge spectroscopy (XANES) measurements under different annealing.1. Well-aligned ZnO nanorod arrays were synthesized by low-temperature wet chemical bath deposition (CBD) method on Si substrate under different conditions. Results illustrated that the ZnO nanorod arrays with a hexagonal wurtzite structure were vertically well-aligned and were densely and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on nanorods morphology were investigated systematically, and the mechanism for the effect of preparation parameters was elucidated based on the chemical process of CBD and basic theory of nucleation and growth process. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. High intensity near-band edge ultraviolet (UV) emission peak were observed in room temperature photoluminescence (PL) spectra for the samples under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO nanorod arrays could be achieved via this low temperature easy-process chemical approach.2. ZnO nanorods were grown on different substrates (quartz glass, Si and ITO glass) by the wet chemical bath deposition (CBD) method at a relatively low temperature of 95"C. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results illustrated that the ZnO nanorods arrays with a hexagonal wurtzite structure were grown densely and vertically on all the substrates, whereas the average diameter and length were found to be closely related to the substrates nature.3. ZnO:N thin films were deposited on sapphire substrate by metal organic chemical vapor deposition with NH3 as N doping sources. The reproducible p-type ZnO:N film with hole concentration of～1017 cm-3 was successfully achieved by subsequent in situ thermal annealing in N2O plasma protective ambient. To understand the mechanism of the p-type doping behavior of ZnO:N film, X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption near-edge spectroscopy (XANES) measurements have been applied to investigate the local electronic structure and chemical states of nitrogen atoms in ZnO:N films.