P-mbe, Method Of Zinc Oxide Thin Films Prepared On Silicon Substrates And The Structural And Optical Properties Of Nanotubes

As an important II-VI compound semiconductor of wurtzite crystalstructure with the wide band-gap of 3.3eV and large exciton bindingenergy of 60meV, which ensures the high efficient excitonic emission atroom temperature, Zinc oxide (ZnO) is regarded as one of the mostpromising materials for fabricating efficient ultraviolet (UV) and blue lightemitting devices. Like GaN compound of wide band gap, the researchabout ZnO has burned white hot in the field of opto-electronics. High quality ZnO thin films have been grown on Al2O3 substrate byMBE. But few studies have been focused on the growth andcharacterization of ZnO grown on Si substrate which will be done in thisdissertation, because Silicon (Si) as another promising substrate is not onlyof interest for the integration of optoelectronic devices but also cheaperand easier to cleave in comparison to sapphire. The major results are givenas following:1. Dependence of ZnO thin films on the substrate temperature has been studied. A series of ZnO thin films are grown on Si substrate with increasing substrate temperature for temperature ranging from 350°C to 700. The results indicate that the qualities of the ZnO thin films grown at low substrate temperatures decrease, because the transfer rate of atoms absorbed on the substrates is too low to transfer to the normal state of the ZnO crystal lattice at the low growth temperature; and the qualities of the ZnO thin films grown at high (>650°C) substrate temperatures is also poor, because the atoms absorbed on the substrate is easy to escape from the substrate. The results of XRD and PL spectra at our experiments indicate that 550 is the optimal deposition temperature for growth of ZnO thin films on Si(111) substrates by P-MBE. And the origin of the ultraviolet luminescence is ascribed to the emission of the free exciton. iii2. Effect of ZnO buffer layer grown at a low-temperature on the quality of ZnO thin films has also been studied. The low temperature buffer layer was epitaxied on the Si substrate at the temperature of 300°C. Non-finite ZnO was grown on the substrate due to the low temperature at which the Zn and O atoms is easy to be absorbed on the substrata, which could relaxed effectively the effects of the lattice mismatch between the substrate and ZnO thin films on the quality of the ZnO films and could reduce the formation of distortion and defects. The results of XRD, AFM, RHEED and PL spectra tell us that the morphology, structure and optical qualities of the ZnO thin film grown on the low-temperature buffer layer at the optimal substrate temperature of 550°C have been improved greatly, which indicates us that high-quality ZnO thin films can be obtained on Si substrate by growing on top of a low-temperature grown ZnO buffer layer.3. Growth and characterization of ZnO nanotube on Si substrate has been studied. The ZnO nanotubes on Si substrate have been obtained via treatments of the initial thin film ZnO layer by -plasma which provides a template to grow ZnO nanotubes. Here O2 -plasma treatment is the + crux to grow ZnO nanotubes on Si substrate. These ZnO nanotubes show excellent field emission properties with turn-on voltage of 2.5 V/μm. The emission current density of ZnO nanotubes is 1mA/cm2 at a bias field of 7V/μm.The ZnO nanotubes grown on Si substrate with high current emission and low turn-on voltage makes the use of ZnO on display and field emission possible.