| ZnO is an important II-VI semiconductor oxide material with a wide direct band gap of3.37eV at room temperature (RT) and a high exciton binding energy of about60meV, which results in exciton stimulated emission at room temperature with high stability. There has been an increasing interest in ZnO due to its distinguished performance in electrical, optical and piezoelectric properties for many applications such as light emitting diodes, liquid crystal display, solar cell, photo detectors, and so on, which has made ZnO experiencing a research boom in modern times.However, un-doped ZnO usually contains various intrinsic defects such as Vzn, Vo, Zm, Oi and so on. These intrinsic defects form either acceptor level or donor level in the band gap that would greatly affect the luminescent properties of ZnO. It will change the defect concentration of ZnO thin films by introducing impurities, so as to improve the crystal quality and optical properties of ZnO thin films. In addition, there remains much controversy regarding the intrinsic defects of un-doped ZnO. Considering the above background, this dissertation revolves around the aspects of crystal growth, structural morphology and doping. And our work focuses on the growth behavior and the optical properties influenced by hep buffer layer and Fe-doped via X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), ultraviolet-visible spectrophotometer and fluorescence spectrophotometer. In this way, some theoretical basis and experimental data are provided for the application of ZnO films. The results are summarized as follows:1. The hep buffer were firstly deposited on Si substrates and then ZnO films were deposited on hep buffer using radio frequency (RF) reactive magnetron sputtering technique. The effects of hep buffer on the microstructure and photoluminescence properties (PL) of ZnO thin films were investigated. It is found that the PL properties of the films are improved after the introduction of hep buffer layer.2. ZnO thin films have been deposited on Ti buffered Si and glass substrate by RF reactive magnetron sputtering. The effects of Ti buffer with different sputtering time on the microstructure, crystallization properties and optical characteristics of ZnO thin films had been investigated. The results revealed that the ZnO film grown on Ti buffer has a better crystal quality and FWHM of (002) diffraction peak decreased with the increasing of sputtering time of Ti buffer, which means that the ZnO thin films was improved due to Ti buffer. However, there is an optimized sputtering time of buffer. The average optical transmittance with over80%in the visible range was obtained and the UV absorption edge shifts to a longer wavelength first, and then to a shorter wavelength with the increasing of sputtering time of Ti buffer. The UV peak located at390nm, two blue peaks located at about435and487nm, two green peaks located at about525and560nm were observed from PL spectra. And the strongest blue light emission of ZnO films was obtained from Ti buffer layer with the sputtering time of10min. The analysis of PL spectra showed that the UV emission may originate from recombination of free exaction. Two blue emission peaks were assigned to the electron transition from the Zn interstitials levels to the top of valence band and the energy levels of Zn interstitials to Zn vacancies, respectively. The green peak located at525nm may correspond to the electron transition from deep oxygen vacancies level to the top of valance band and the green peak located at560nm was attributed to oxygen interstitials and oxygen vacancies.3. Fe-doped ZnO (ZnO:Fe) films were deposited on the glass and Si substrates via RF reactive magnetron sputtering and the effects of substrate temperature on the microstructure, surface morphology and optical properties of ZnO thin films were studied. The results revealed that the film had a (100) preferred orientation when ZnO:Fe film was deposited at RT, while (002) preferred orientation of ZnO:Fe thin film was fabricated exceed150℃. And the intensity of (002) diffraction peaks increases as substrate temperature increases. It means that the crystallization quality and growth orientation of ZnO:Fe film was improved by appropriate substrate temperature. In addition, with the increasing of substrate temperature, the band gap (Eg) of ZnO:Fe increase firstly and then decrease. The increasing of Eg which was caused due to the improvement of the quality of film and the decreasing of Eg was likely due to the raising the concentration of carriers caused by increasing substrate temperature. The PL measurements revealed a violet (410nm), a blue (456nm) and a green (515nm) emission and the mechanism of luminescence was discussed in detail. |
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