Improvement of CuAlO₂thin film electrical conduction by the anisotropic conductivity

CuAlO₂thin films with (015) preferential orientation growth have been synthesized on quartz substrates using radio frequency (rf) magnetron sputtering at low temperature. Via the optimized postannealing condition (in N₂preserved ambient at 900 °C for 5 h), the preferential orientation of the films changes from (015) to (001) direction. The use of a higher conductivity at theabplane of CuAlO₂compared with that along thecaxis, reduces the resistivity of the film at room temperature to 37 Ω·cm from that of the as-deposited, 4.62 × 10⁴Ω·cm. The positive Hall coefficient (+183.6 cm³/C) and the large mobility (4.07 cm²/V·s) suggest that CuAlO₂thin films arep-type semiconductors with good conduction path. The temperature dependence of conductivity indicates that CuAlO₂thin films obey a thermal-activation theory when the temperature is above 190 K, but below 185 K a two-dimension variable-range hopping mechanism becomes dominant.