Fabrication and characterization of p-type transparent conducting oxide CuAlO2 thin film

• Main Authors: Cheng-Hung Shih, 施政宏
• Other Authors: Bae-Heng Tseng
• Format: Others
• Language: en_US
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/58q92a

博士 === 國立中山大學 === 材料科學研究所 === 96 === In this thesis, we investigate the synthesis of CuAlO2 on sapphire (0001) substrate by rapid thermal annealing of an Al2O3/Cu2O/sapphire structure above 1000oC. We examine the effects of growth conditions on the structural, formation mechanism, and optical and electrical properties of CuAlO2 thin film. The film prepared at 1100 oC in air was with epitaxial structure as verified by X-ray diffraction methods. Gas ambient, temperature ramp rate and reaction temperature are crucial parameters for the formation of CuAlO2 film. We found that single-phase CuAlO2 thin films formed in air ambient by a rapid temperature ramp rate above 1000oC. A slow temperature ramp rate and a pure oxygen ambient might lead to the appearance of second phase such as CuAl2O4. Optical gap of our films were determined to be 3.75 eV. Optical transmittance depended on the temperature of thin film reaction. The best transmittance obtained was 60 % by annealing at 1100 oC in air. Photoluminescence and cathodoluminescence measurements showed that the two peaks obtained are around 3.4 eV and 1.8 eV corresponding to UV and red emission. As a result of CuAlO2 has an indirect gap about 1.8 eV. The electrical conductivity of the film related to the oxygen content was investigated by the annealing experiments in oxygen-deficient (vacuum) and oxygen-excess (air) ambient. The sheet resistance of CuAlO2 increases consistently with an increase in the duration of the vacuum annealing. Further annealing in air restores the sheet resistance to the original value. The highest conductivity obtained in this work was 0.57 S/cm. Metal contacts to CuAlO2 were also studied in this work. The current-voltage characteristics showed that Cu, Al, Ni or Au could form Ohmic contact to CuAlO2. The lowest contact resistance was using Al metal. However, when the contacts were post-annealed above 300oC, the contact resistance was increased.