| Summary: | 碩士 === 國立中興大學 === 材料科學與工程學系所 === 98 === Transparent Conducting Oxides (TCOs) are widely used in solar cells, touch panels and liquid crystal displays (LCDs), due to its high electrical conductivity and high transparency in the visible light spectrum. At present, the well-known TCOs, such as ZnO, In2O3, SnO2, are all n-type conductors. In order to fabricate a hetero-junction p-n diode, to develop the p-type TCOs is very important.
This experiment used dc reactive sputtering system to deposit the Sr-Cu-O films on glass and silicon substrates. The target material used in the sputtering was prepared by melting a mixture of Cu2O and SrCO3 in vacuum. After deposition, the films were annealed under ambient atmosphere. The microstructure and optoelectronic properties of the Sr-Cu-O thin films were investigated as a function of O2/Ar ratio and annealing temperature. Characterization of the Sr-Cu-O thin films were carried out by XRD, HRTEM, SEM, ultraviolet/visible spectrometry and Hall measurement.
The XRD showed that the as-deposited thin film was amorphous. The 300℃ annealed film was found to consist of a mixture of CuO, Cu2O, SrCuO2. When the annealing temperature increased to 400°C, the XRD peak was similar to the 300℃ annealed, but the diffraction peaks were stronger, and the SrCu2O2 phase was present in the film. When the annealing temperature was up to 500℃, the phase transformation occurred again. The Sr4Cu6O10 disappeared entirely and the peaks of SrCu2O2 were getting stronger. The 400℃ annealed film has a higher conductivity than the 300 and 500℃ annealed films. It was observed by HRTEM that the 400℃ annealed film contained less nanopores, which can explain why film annealed has a better electrical conductivity. In addition, the 500℃ annealed film had a better transmission and higher band gap. This may be attributed to the increased content of SrCu2O2 phase observed in the XRD spectra. The lower transmission of the film in visible light was affected by presence of CuO and Cu2O phases. At wavelength of 500 nm, the transmission of the film was nearly 50 % in the near IR range. The films’ direct band gap of the film was estimated to be about 2.79 eV.
The increase of deposition O2/Ar ratio led to the increase of optical transmission and band gaps. The Hall measurement demonstrated a p-type conduction behavior for the Sr-Cu-O films, and its carrier concentration and conductivity were increased by the presence of extra oxygen in the films. These results are also consistent with the published literatures.
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