| Zinc oxide (ZnO) is an important II-VI direct band gap semiconductor material,which has band gap of3.37eV at room temperature (RT), and the exciton bindingenergy as high as60meV. Usually ZnO has hexahedron wurtzite structure at the aircondition. It has been investigated extensively due to its distinguished performance inelectrical, optical and piezoelectric properties making suitable for many applicationssuch as light emitting diodes, photodetectors, electroluminescence, transparentconductive film, surface acoustic waves device and so on. However, pure ZnO usuallycontains various intrinsic defects such as Zn vacancies, interstitial Zn, O vacancies,interstitial O, and antisite O. These intrinsic defects would greatly affect theluminescent properties and microstructure of ZnO. By introducing extrinsic dopant,the defect environment is changed, which lead to that luminescent properties andmicrostructure of ZnO were improved.This thesis is focused on the hotspots and challenges in the field of ZnOmaterials research. Metal-doped ZnO films are prepared by radio frequency reactivemagnetron sputtering technique. The crystalline and optical properties of thin filmswere investigated by the X-ray diffraction (XRD), X-ray photoelectron spectroscopy(XPS), scanning electron microscope (SEM) and fluorescence spectro-photometer. Inthis way some experimental data and the theoretical basis are provided for theapplication of ZnO films. The results are summarized as follows:1. The study on mirostructural characteration and optical properties of ZnO:Curevealed that ZnO films had a stronger preferred orientation toward the c-axis and theFWHM of the ZnO (002) diffraction peaks decreased after Cu-doping, and thevalence state of Cu in ZnO:Cu film was mainly+1. As for ZnO:Cu films, theminimum full width at half maximum (FWHM) would be obtained and the residualcompressive stress of the ZnO:Cu films decreased with the stubstrate temperatureincreasing to350℃, which indicated that the crystallization quality of ZnO:Cu filmwas improved by appropriate substrate temperature. Four main emission bands in thePL spectra, two blue peaks located at about424and485nm and two green peakslocated at about528and568nm, were observed. After annealing in vacuum, the crystal quality of ZnO:Cu thin film was markedly improved. Meanwhile, the intensityof emission peaks increased noticeably.2. The Al-doped ZnO (ZnO:Al) thin films with different Al contents weredeposited on ZnO buffer layer and the microstructure, surface morphology,luminescence properties of thin films were studied. The results of XRD and SEMrevealed that FWHM of (002) diffraction peak first increased and then decreased withincreasing Al concentration, which indicate that crystal quality of ZnO thin films wasimproved due to Al-doped. The transmittance decrease with increasing Alconcentration in the visible range, and the ZnO:Al films show the averagetransmittance above70%. Two Blue peaks located at444nm (2.80eV) and483nm(2.57eV) and weak green peak located at about521nm (2.38eV) were observedfrom the PL spectra and the mechanism of luminescence was discussed. The analysisof PL spectra showed that the green emission peak (521nm) originated from electrontransition from the conduction band to O vacancies; two blue emission peaks (444nmand483nm) were assigned to the electron transition from both the interstitial Znlevels to the top of valence band and the energy levels of O vacancies to the top ofvalence band.3. Ti-doped ZnO (ZnO:Ti) thin films were deposited on the glass and Sisubstrates, and the microstructure, surface morphology, luminescence properties ofthin films were studied. The structural analyses of the films indicated that they werepolycrystalline and had a hexagonal wurtzite structure on different substrates. WhenZnO:Ti thin film was deposited on Si substrate, the film had a c-axis preferredorientation, while preferred orientation of ZnO:Ti thin film deposited on glasssubstrate changed towards (100). Finally, we discussed the influence of the oxygenpartial pressures on glass-substrate of ZnO:Ti thin films. The results indicated that thecrystallization quality of ZnO:Cu film was improved by appropriate oxygen partialpressures. The average optical transmittance with over93%in the visible range wasobtained independent of the O2:Ar ratio. The PL spectra measured at roomtemperature revealed four main emission peaks located at428,444,476and527nm.Intense blue-green luminescence was obtained from the sample deposited at a ratio ofO2:Ar of14:10sccm. The results showed that the oxygen partial pressures had an important influence for photoluminescence (PL) spectra and the origin of theseemissions was discussed. |
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