Raman Properties Of Ag Doped ZnO Films And Nanostructures

As an II-VI semiconductor material, zinc oxide (ZnO) is widely used in the fileds of field effect transistors, gas sensors, piezoelectric devices and solar cells. Furthermore, ZnO is considered as a promising optoelectronic material with potential applications in light emitting diodes and laser diodes due to its wide direct bandgap (3.37eV) and large exciton binding energy (60meV). The structural, physical and optical properties of ZnO are closely depended on the deposition method and its parameters, post-treatment and dopants. Ag is a good electric conductor with relatively low optical absorption coefficient in the visible region. As a group IB element, if incorporated on substitutional Zn sites, also it can act as an acceptor in ZnO. Raman spectroscopic technique is one of the most useful methods to gain insight into the microscopic structural effects of crystal materials. Important information about the crystal structure, any distortion of the lattice, crystal defect and phase transformation can be shown in Raman bands.In this thesis, the Ag doped ZnO films and nanostructures were synthesized using different technic on sapphire substrate. The influence of Ag doping on the properties ZnO were investigated and the results are elucidated as follows:ZnO:Ag films were prepared on c-plane sapphire substrates by pulsed laser deposition. The influence of substrate temperatures on the properties of ZnO:Ag films were studied in detail. The results indicated that the content of Ag in ZnO:Ag films increased with the increasing growth temperature. Meanwhile, the ZnO (002) peak shifted to lower angle direction. A local vibrational mode (LVM) at492cm-1induced by doping Ag was observed in the Raman spectra of all the ZnO:Ag films. The peak position of LVM at492cm-1did not changed even under different growth temperature.ZnO:Ag films were prepared on c-plane sapphire substrates by pulsed laser deposition method. The structure and Raman spectra of the as-deposited and the ZnO:Ag films annealed at700℃were investigated. The results revealed that the incorporation of Ag in ZnO:Ag film cause the (002) peak shifted to lower angle direction in XRD patterns. The A1(LO) mode resulting from oxygen vacancies and zinc interstitials was observed to be very strong in the Raman spectra of the as-deposited and annealed ZnO:Ag films. The peak position of the LVM at492cm-1in the Raman spectra did not changed after the annealing treatment.Un-doped ZnO micro/nanowires and Ag doped ZnO nanostructures were synthesized by a chemical vapour deposition method. ZnO micro/nanowires were prepared using ZnO powers as resource. The ZnO micro/nanowires exhibit perfect hexagonal structure and good optical properties. The shifts of Raman peak indicated that a tensile stress and centain defects such as oxygen vacancies were existed in the ZnO micro/nanowires. The Ag doped ZnO nanostructures were synthesized using ZnO/Ag2O mixed powers as resource on sapphire substrates. The results indicated that the position of the substrates could affect the morphologies of ZnO:Ag nanostructures. The different structures were most likely linked to dynamic crystal growth processes at different oxygen concentration or the thermodynamical equilibrium during the growth process. In Raman spectra we also found LVMs at492cm-induced by doping Ag and the peak positions are independent to the shape of nanostructures.In our experiment, the LVM at492cm-1induced by doping Ag were observed in the Raman spectra of all the ZnO:Ag samples and its peak position is independent to the preparation methods, growth temperatures, and morphologies. It means that the LVM can act as an indication of the incorporation of Ag in ZnO samples.