Synthesis And Photoluminescence Of Si And ZnO Nanowires

The study of the fabrication and characters of one dimensional SiNWs, ZnO nanowires have stimulated much attention in the nano-science and technology realm. If SiNWs and ZnO nanowires can be directly assembled to nano-heterojunctions,it would be providing experimental and theoretical foundation for the development of the bottom-up fabrication in the nano-electron industry.In this thesis, one dimensional SiNWs, ZnO nanowire arrays and Si/ZnO nano/micrometer heterojunctions have been synthesized by CVD method. The as-prepared samples were characterized by using of transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and photoluminescence (PL) spectrum and other analysis technologies. The study of growth structure, morphology and PL behavior of SiNWs and ZnO nanowires will show some valuable application results.1. At the deposition temperature of 350, 380, 400℃, SiNWs had been synthesized by chemical vapor deposition (CVD) method with Au as catalyst. The theoretical analysis and experimental studying indicated that the growth mechanism was fit for the vapour-liquid-solid (VLS) mode. The diameter of single crystal SiNWs were related with the substrate temperature. The experimental results showed that as-prepared SiNWs had different morphologies and microstructures as a result of the disequilibrium between the deposition velocity of Si and O vapor atoms and the growing speed of SiNWs. Because the growth rate was the same as the depositing velocity of gaseous Zn and O atoms, SiNWs synthesized at 380℃condition had good growing orientation and higher crystal structure. So the PL spectra revealed that the emission peek was located at 596nm and consisted with a red band peek, but occurred 7nm blue shift.2. Three kinds of ZnO nanowire arrays were simultaneously fabricated on Au coated (110) silicon wafers by vapor-phase transport method of heating the mixture of ZnO and graphite powders in molar ratio of 1:1 at 650, 750, and 900℃temperature zones. Structural analyses revealed that the morphologies and crystal microstructures of ZnO nanowire arrays were related with the substrate temperature. It displayed that the structures of ZnO nanowire arrays were uniform, and ZnO nanowire arrays grew alone the (002) crystal direction at the temperature of 650 and 750℃. But at 900℃condition, the velocity of gaseous Zn and O atoms down to the substrates was larger than the growth rate of nanowires. The quick growth of ZnO nanowires caused these nanowires to bend on the substrate or twist together indeed. And the PL spectra showed that the emissions were consisted with an ultraviolet and another wide green band peak, and the emission peaks were located at about 379.6nm and 488.8nm, respectively. The ultraviolet emission peak was caused by the transition of near band edge, and the PL peak at about 488.8nm corresponded to the electronic excitoning of the vacancy lever in the ZnO semiconductor.3. By using of the above fabricating methods, epitaxial ZnO nanowires were grown on the SiNWs. And the nano/micrometer-scale Si/ZnO heterojunctions have been directly assembled. The morphologies and growth structures of products were checked and analyzed by SEM. The test found that the ZnO nanowires were tended to wrapping on the SiNWs, then formed nano/micrometer-scale Si/ZnO core-shell heterojunctions. In the end, the special growth mechanism of Si/ZnO core-shell heterojunctions was explained and discussed by using of the molecular dynamics and VLS growth mechanism.