Synthesis And Research Of ZnO And SiC Semiconductor Materials On Graphite Substrate

GaN, SiC and ZnO are typical wide band-gap semiconductor materials, which are expected to break through the material limitations that the first generation semiconductor materials, such as Si and Ge, as well as the second generation semiconductor materials represented by GaAs and InP are facing the applications for high-power optoelectronics and power electronic devices. Therefore, these wide band-gap semiconductors are also called the third generation semiconductor materials. ZnO, which is a direct band-gap semiconductor, has been regarded as one of the most promising candidates for the next generation of short-wavelength light emitting diode (LED) and lasing devices due to its wide band gap (3.37eV) and large exciton binding energy (60meV) at room temperature. At the same time, ZnO has many other advantages, such as, good thermal stability, low cost, abundant raw material, and environmental friendly, etc. In addition, SiC has been regarded as one of the most ideal material for manufacturing high frequency, high power electronic devices by virtue of its superior thermal and electrical properties, such as, high breakdown field strength, high carrier saturation velocity, high thermal conductivity, excellent resistance to oxidation and corrosion. However, the heat-dissipation performance is closely related to the substrate materials, which will significantly affect the performance and life of the high-power optoelectronic devices. The advantages of graphite lie in its excellent mechanical and chemical stability, especially the higher electrical and thermal conductivity. And it offers the significant opportunity for preparing transferable devices due to its weakly bonded layer structure. It has the prospect of becoming the ideal substrate material for the high-power optoelectronics and power electronic devices. To solve the problems mentioned above, our researches were focused on the theme "Synthesis and Research of ZnO and SiC semiconductor materials on graphite substrate". The research contents and conclusions are listed as following:First, the photoluminescence (PL) properties of the polycrystalline pyrolytic graphite samples was investigated. The results indicate that the polycrystalline pyrolytic graphite with the c-axis preferred-orientation shows an ultra-narrow line spectrum (～1.8A) emission behavior. In addition, the ZnO films were grown on graphite substrate by ultrasonic spray pyrolysis (USP) method. Dense ZnO films comprised of pyramidal-shaped ZnO nanosheets were uniformly distributed on the substrate. And strong near-band edge ultraviolet emission peaks were observed in room temperature PL spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable. The crystalline quality and the optical properties of the as-grown ZnO films could be improved via optimizing both the substrate temperature and the growth time.Second, the optical properties of the ZnO nanorods (NRs), which were grown on the graphite substrates using hydrothermal method, had been investigated. The results indicate that the high optical qualities of ZnO NRs were demonstrated by the dominant near-band edge emission and nearly undetectable deep level emissions after annealing treatment. And the extremely low average reflectance of0.45%was obtained for the ZnO NRs/graphite hybrid structure in the spectra range from200to1100nm, which showed a good light-trapping effect. In addition, the crystalline quality of the as-grown ZnO NRs could be improved via optimizing the substrate temperature, the growth time, and the annealing temperature.Third, the ZnO/SiO2/graphite hybrid structure was fabricated on the graphite substrate by magnetron sputtering and Electron beam evaporation methods. The current-voltage characteristics exhibit an obvious rectifying behavior with a leakage current of10-4A at-8V. And an interesting negative capacitance (NC) phenomenon was also observed. In addition, the excellent heat conduction performance of the ZnO/SiO2/graphite hybrid structure was experimentally demonstrated. And the physical mechanism of negative capacitance phenomenon has been analyzed and discussed briefly.Fourth, β-SiC thin films were synthesized directly on graphite substrate by the hot filament chemical vapor deposition (HWCVD) method at low temperature. Graphite was functioned as both substrate and carbon source for the as-grown β-SiC films. And its crystalline quality can be remarkably improved under optimized annealing conditions. The possible growth mechanism was proposed. In addition, SiO2/β-SiC/graphite hybrid composite can be formed after post annealing treatment in ambient of argon containing trace amounts of oxygen. According to the Ⅰ-Ⅴ curve, the β-SiC based MOS (Au/SiO2/β-SiC) device shows a obvious rectifying diode like behavior with a leakage current of10-3A at-3V.