| Summary: | 碩士 === 正修科技大學 === 電子工程研究所 === 98 === In this study, aluminum and yttrium dually doped zinc oxide (AZOY) thin films have been prepared by direct current reactive magnetron sputtering on glass substrate. The AZOY films were deposited at different sputtering pressures (5 mTorr, 7 mTorr, 9 mTorr, 11 mTorr, and 13 mTorr). The effects of sputtering pressure on the structure properties, electrical properties, optical properties, and surface morphology of AZOY thin films were investigated. To study the optical properties of the AZOY thin films, the transmission and reflection spectra of the AZOY films were measured using a UV-VIS spectrometer. The simulation of optical transmittance and reflectance spectra was carried out using commercially available software with wavelength ranging from 400 to 2500 nm, to obtain plasma frequency, relaxation time and optical mobility of the AZOY films.
From the XRD results, it is found that all diffraction patterns of AZOY films exhibit only the ZnO (002) peak, suggesting c-axis preferred orientation. In addition, the full-width at half-maximum (FWHM) values of (002) peak increases from 0.33 ° to 0.36 ° as the sputtering pressure increases. This shows that the crystal quality deteriorates slightly and the average crystallite dimension gets smaller. The electrical properties of the films were examined by the Hall Effect measurement. The results indicate that the lowest resistivity of 4.26×10-4 Ω-cm, the maximum Hall mobility of 31 cm2/Vs and concentration of 4.73×1020 cm-3 were obtained for the sample deposited pressure at 7 mTorr. The mobility and concentration of the AZOY films decreased as the deposition pressure increased. Furthermore, the resistivity gradually increases as the mobility and concentration decreases.
For all the AZOY films, the average transmittance in the visible region is around 83-84%. The increase in deposition pressure which is correlated with the decrease of the measured electrical concentration leads the absorption edges of the films to redshifted, and the optical energy band gap of the AZOY films decreases from 3.687 eV to 3.576 eV. The decrease in optical band gap can be attributed to the Burstein-Moss effect. The refractive index in the visible wavelength range determined by the spectroscopic ellipsometry is 1.75-2.05. The thickness of thin films decreased and the surface roughness increases as the sputtering pressure increases. The tendency of surface roughness obtained from variation ellipsometry measurement is consist with that obtained from AFM measurement.
The plasma frequency and relaxation time can be extracted from the simulation of measured optical spectra. The plasma frequency of the AZOY films decreased from 1.12×1015 rad/s to 9.39×1014 rad/s and the relaxation time decreases as the sputtering pressure increases. After that, the optical mobility can be calculated from plasma frequency and relaxation time. From the comparison between the optical mobility and hall mobility, it was found that the optical mobility is higher than hall mobility. Thus, it was concluded that the increase of deposition pressure increases the grain boundary scattering of AZOY films.
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