Experimental And First Principle Study On Na-doped ZnO Nano-materials

ZnO is well known as an important semiconductor with a wide direct band gap of3.37eV and large exciton binding energy of60meV at room temperature. The study of nanostructured ZnO has attracted much interest in the last few years due to its potential applications in such fields as photocatalysis, piezoelectricity, optoelectronics, photovoltaic conversion, and gas-sensing devices. The synthesis of stable p-type ZnO nanostructures would be the key to open up substantial opportunities for electronic and optoelectronic nanodevices. However, it is still difficult to make stable p-type conductivity in ZnO, since the dopant solubility is low and the defects compensate for the substitutional impurity levels through the formation of deep level traps rather than operative shallow acceptors.In this regard, the work was mainly focused on the preparation of ZnO nanostructures and mechanism of p-type doping, especially Na-doping, by experiment, combined with first principle approaches. The work included:(1) ZnO nanorods arrays were prepared by controlling reaction temperature, system pressure, substrate and materials of buffer layers in a unilateral open quartz boat. The optimum growth condition was found. Based on analysis of the balance of reaction temperature and system pressure, balance theory was proposed for controlling the morphology of nanostructures.(2) Base on the balance theory, ultralong micro/nano-fiber were prepared under extreme condition. Spatial linear nucleation theory was proposed.(3) Na-doped ZnO nanorods arrays with various Na source were prepared by CVD method. We prepared Na-doped ZnO nanorods arrays with sodium pyrophosphate and sodium tripolyphosphate, respectively, under high and low temperature CVD method. Various tests were carried out. Combined with first principle calculation, we demonstrated that Na dopants were mainly occupied Zn site in crystal lattice. A practical and effective method of p-type ZnO realizing was raised, which is increasing the solubility of NaZn in ZnO by the attractive interaction between Vo and NaZn- (4)"Na-doped ZnO nanorods arrays homojunction were prepared under high and low temperature CVD method and hydrothermal process.(5) Base on the balance theory, ZnO micro-comb arrays were prepared with perfect orientation. First single As-doped ZnO micro-comb p-n homojunction were made by thermal diffusion method. With photolithography and e-beam vaporation tech, wholly As-doped ZnO micro-comb and semi As-doped ZnO micro-comb were made into As-doped p-type FETs and p-n homojunction UV-light detectors.