||This thesis focuses on studying the structural and optical properties of nonpolar a-ZnO thin films grown on r-Al2O3 substrates (a-ZnO/r-Al2O3). The crystallographic qualities and orientations of a-ZnO thin films grown by rf-sputtering are analyzed by X-ray diffractometry (XRD) through θ-2θ scan, φ-scan, rocking curve and GIXRD. The morphology and cross section of the thin films grown by different parameters were analyzed by SEM. From PL measurement, we knew the properties of carries.|
The growth of a-ZnO epitaxial thin films was attempted at different substrate temperatures. The epitaxial relations between the thin films and substrates have been determined by the φ-scans to be ZnO || [¯1 011]Al2O3 and [1¯1 00]ZnO || [1¯2 10]Al2O3. The full width at half maximum (FWHM) of rocking curve for each sample decreases with increasing substrate temperature. From SEM observations, the surface morphology demonstrates elongated granular structures along the c-axis.
The properties of the a-ZnO thin films depend on the PAr:PO2 ratios and 2.8:1 gives the best results byθ-2θand rocking curve . When the flux of oxygen was increased, the aspect ratio of the elongated grains would decrease. From room-temperature photoluminescence (RT-PL) spectroscopy, the zinc vacancy and oxygen content determine much of the observed material properties of the a-ZnO thin films. According to variable-temperature dependent PL spectroscopy, the energy positions of FX, DAP and VZn peaks do not shift as a result of temperature change, which we contemplate as a 3D to 2D transition of the electronic behaviors as the temperature decreases.