Preparation And Properties Of ZnO Thin Films And Nanostructures

Zinc oxide (ZnO) is an important II-VI direct band gap semiconductor material, which has band gap of 3.37 eV at room temperature, and the binding energy of exciton as high as 60 meV. ZnO has recently attracted much attention due to its distinguished performance in electrical and optical making it suitable for many applications such as solar cells, light emitting diodes, surface acoustic wave device, ultraviolet (UV) photodetector and so on.In this thesis, we prepare highly c-axis oriented ZnO films on the growth side of diamond-film-substrate; synthesize ZnO nanorods (NRs) at low temperature on various chemical vapor deposited (CVD) diamond substrates and study their optical and electrical properties. The ZnO nanorods/plates are obtained on Si substrate and study their photoluminescence (PL). Some innovative results are obtained and the details of our work are as follows:1. We prepare highly c-axis oriented ZnO films, by radio-frequency magnetron sputtering, on the growth side of freestanding chemical vapor deposited diamond-film-substrate. The morphology, structure, and optical properties of the ZnO films deposited are strongly dependent on the thickness of the buffer layer. Experimental results show that low-temperature ZnO buffer layer can effectively improve the quality, stress and optical properties of films. The optimized thickness of ZnO buffer layer is about 10 nm to realize high quality ZnO films having small compressive stress and high intensity ultraviolet emission.2. A facile hydrothermal method has been developed to grow ZnO NRs on various diamond substrates, such as undoped/doped polycrystalline diamond films and single crystal diamonds. ZnO NRs have a certain orientation distribution due to ZnO NRs grow perpendicularly to the facets of diamond. ZnO NRs grow on the polished surface of freestanding diamond films and single crystal diamonds with the growth orientation perpendicular to the substrate surface. The PL of ZnO NRs indicated that the as grown samples have high intensity ultraviolet emission. The ZnO NRs/p-diamond heterojunctions have been prepared and the current-voltage (I–V) examination results represent a good diode behavior. Furthermore, the heterojunction shows typical photoconduction characteristics under UV illumination and can be used for UV detectors.3. The ZnO nanorods/plates are obtained via hydrothermal method on Si substrate. The growth mechanism of ZnO nanorods/plates and nanoplates are investigated. It is found that the introduction of the etched Al film plays a key role in the formation of ZnO nanorods/plates. The products consist of nanorods with average diameter of 100 nm and nanoplates with thickness of 200–300 nm, which are uniformly distributed widely and grown perpendicularly to the substrate. The PL of ZnO nanorods/plates are also investigated. The results indicate the annealing process is favorable to enhancing the intensity of UV emission and suppressing the green emission of ZnO nanorods/plates.