Efforts to improve carrier mobility in radio frequency sputtered aluminum doped zinc oxide films
Journal of Applied Physics
This study addresses the electrical and optical properties of radio frequency magnetron sputtered aluminum doped zinc oxide ͑ZnO:Al͒ films. The main focus was on the improvement in carrier mobility to achieve simultaneously high transparency for visible and particularly near-infrared light and low resistivity. The influence of Al concentration in the target, film thickness, sputter power, deposition pressure, and substrate temperature on material properties was investigated. The structural,
... The structural, compositional, electrical and optical properties were studied using x-ray diffraction, secondary ion mass spectrometry ͑SIMS͒, room temperature Hall effect measurements and spectral photometry, respectively. All ZnO:Al films were polycrystalline and preferentially oriented along ͓002͔. The grain size along the direction of growth increased with higher Al doping and with increasing film thickness. The SIMS measurements revealed that the Al concentration in the film was nearly the same as in the target. Carrier concentration N and mobility are determined by the target Al concentration. In addition is influenced by the film thickness and the sputter pressure. For each Al concentration, the highest was generally observed at low deposition pressures. By using a target with low Al 2 O 3 concentration of 0.5 wt %, could be improved up to 44.2 cm 2 /V s while maintaining the electrical resistivity as low as 3.8ϫ10 Ϫ4 ⍀ cm. For these films the transparency in the near-infrared wavelength range strongly improved which makes them particularly interesting for the application in optoelectronic devices like thin-film solar cells. The -N dependence for films deposited under diverse conditions was studied to identify a practical limit for .