Sputtering deposition of Ga-doped ZnO (ZnO : Ga) thin films was carried out using the helicon-waveexcited plasma sputtering (HWPS) method. The films sputtered above 150 °C had a preferential {0001} orientation. According to the surface-damage-free nature, the films having featureless surface morphology exhibited an optical transmittance greater than 80% in the visible spectral wavelengths. However, because the deposition temperature was limited to 250 °C, the electron mobility was limited to as low as 2-3 cm 2 /V s due to the small grain size (∼ 25 nm). The results indicate that ZnO : Ga films deposited by HWPS can be used in the transparent conducting oxide layer, provided that higher electron mobility is achieved.

CuAlO2 polycrystalline films were deposited by the helicon‐wave‐excited plasma sputtering (HWPS) method at 700 °C. The best full‐width at half‐maximum value of the (006) CuAlO2 X‐ray diffraction peak was 0.19 degrees, which was similar to those reported previously using other deposition methods. While, noncrystalline Cu–Al–O films were deposited by a conventional RF sputtering method. Using this p ‐type transparent conducting oxide (TCO) film and an n ‐type ZnO film deposited by HWPS, a n ‐type ZnO/p ‐type Cu–Al–O heterojunction diode was fabricated. Optical transmittance of the device was approximately 80% in the near infrared region. The rectifying current–voltage characteristics with a threshold forward voltage approximately 1.4 V were obtained. These results are the first step toward realizing an electrical/optical device using p ‐type CuAlO2 or Cu‐Al‐O films. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)