Unraveling the conduction mechanism of Al-doped ZnO films by valence band soft x-ray photoemission spectroscopy

Gabás, Mercedes; Gota, Susana; Ramos-Barrado, José Ramón; Sánchez, Miguel; Barrett, Nicholas T.; Avila, José; Sacchi, Maurizio
January 2005
Applied Physics Letters;1/24/2005, Vol. 86 Issue 4, p042104
Academic Journal
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 ∼150 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.


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