Preparation And Photoelectric Properties Of P-type Sb-doped ZnO Nanorods

Nanoscale semiconductors have drawn public attention since the development of miniaturized electronic devices, and ZnO nanostructure crystals show a great potential in the photoelectric field. Although ZnO has high performance in electronic devices, it has not been used in industrial application filed owing to the difficulty of obtaining low costing and stable p type ZnO semiconductors. I or V group elements are generally used in doping ZnO to get p type conductivity, and there has been a important progress in fabricating p type Sb:ZnO. Physical vapor deposition methods are usually used to fabricated p type ZnO at present, while less research has been made for solution-based methods, therefore more research of solution-based methods for p type ZnO should be made.Here in this dissertation, a solution-based method, electrodeposition, was used to fabricate Sb:ZnO nanostructures. The crystal growth process of Sb:ZnO was studied systemically, and Sb:ZnO nanorods with high crystal quality and good morphology were obtained to fabricate ZnO-based nano-electronic devices. Properties of Sb:ZnO and ZnO-based nano-electronic devices were characterized carefully. Furthermore, the origin of p-type conductivity of Sb:ZnO nanorods and the local structure around Sb ions were investigated, which gives a theoretical guidance for syntheses of Sb:ZnO with better properties. The main work and achievements are summarized as follows:1) Controllable synthesis and properties of Sb:ZnO nanostructures electrodeposited at different applied potentials. Electrochemical process of Sb:ZnO crystal growth in different precursor solutions was studied via cyclic voltammetry, and the applied potential window ranging -0.5V to -0.9V was designated. The effect of applied potential on growth process, surface morphology, optical properties and Sb-doped content in ZnO were studied. It was found that the morphology and crystal quality can be adjusted via changing the applied potential, and -0.8V was found to be suitable to gain fine Sb:ZnO nanorods.2) Controllable synthesis and properties of Sb:ZnO nanostructures electrodeposited at different precursor solutions. The effect of precursor concentration ratios on nucleation process and nucleation rate of Sb:ZnO crystals in initial deposition stage was studied. The effect of SbCl3 concentration and solution pH on Sb:ZnO crystal growth and properties was investigated, too. It was found that various morphology and different Sb-doped contents can be obtained via changing precursor solutions.3) The effect of substrates and annealing process on Sb:ZnO properties. We studied the Sb:ZnO crystal growth process and the effect of substrates on Sb:ZnO crystal properties. High quality Sb:ZnO nanorod arrays were fabricated via depositing a seed layer on ITO substrates using a sol-gel method in advance. A dense-arranged Sb:ZnO nanorod arrays with good quality can be obtained when the electrodeposition was conducted on a conductive woven fibers substrates. Furthermore, dendritic Sb:ZnO nanostructures and ZnO homojunction based on single nanorods were fabricated by a two-step deposition process. The effect of annealing process on Sb:ZnO properties were studied, too.4) Electrical transport behavior of Sb:ZnO-based nanodevices. Measuring the electrical properties of nanorod arrays and confirmation of p type conductivity of Sb:ZnO were conducted in this part. The electrical transport behavior of single Sb:ZnO nanorods at different temperature and atmosphere were studied, the device was constructed via electron beam lithography. Field effect transistors based on single Sb:ZnO nanorods were constructed by a ion beam deposition method, and the p type conductivity of the single Sb:ZnO nanorod was confirmed.5) The origin of p-type conductivity of Sb:ZnO nanorods and the local structure around Sb ions. To probe the origin of p-type conductivity in Sb-doped ZnO, a careful and detailed synchrotron radiation study was performed. From the XPS and XANES results, we verified that the Sb was in an oxidation state between +3 and +5. The EXAFS and XPS investigations provided the evidence for the formation of the complex defects comprising substitution Sb ions at Zn sites and Zn vacancies within the Sb-doped ZnO lattice. Such complex defects result in the increases of Sb-O coordination number and the Sb valence and thereby lead to the p-type conductivity of Sb-doped ZnO.