Unraveling the conduction mechanism of Al-doped ZnO films by valence band soft x-ray photoemission spectroscopy -: art. no. 042104

We report on the correlation between the electrical behavior and valence band spectra of undoped and Al-doped ZnO films, obtained by using x-ray photoelectron spectroscopy. Although Al-doping can induce a conductivity increase of two orders of magnitude, we show that the gap persists and there is no semiconductor-metal transition upon doping. For the 3% Al-doped ZnO film, we measure a reduction in the band gap of similar to150 meV with respect to the undoped and the 1% doped films. Our results suggest that the band conduction mechanism proposed for undoped ZnO at room temperature still dominates the conduction process in doped films. (C) 2005 American Institute of Physics.