Electrical conductivity and photoresistance of atomic layer deposited Al-doped ZnO films

Al-doped ZnO films were deposited by the atomic layer deposition (ALD) on both glass and sapphire (0001) substrates. The Al composition of the films was varied by controlling the Zn:Al pulse cycle ratios. The films were characterized by the atomic force microscopy, x-ray photoelectron spectroscopy, x-ray diffraction, and optical measurements. The Film resistivity was measured as a function of Zn:Al cycle ratios as well as temperature for films grown at various substrate temperature used for ALD deposition. The resistivity of the ALD grown films decreases significantly, and so as the increase in the carrier concentration as the cycle ratio increases. The systematic measurements of temperature dependence of resistivity of films at various cycle ratios clearly demonstrate the crossover of the metal-semiconductor-insulator phase with the function of temperature as well as the cycle ratios. The average transmission of all films is greater than 85% and the optical absorption increases significantly in the visible region as the cycle ratio increases. The authors observed a remarkable dependence of photoresistance on electrical conductivity for ALD-grown films with varying cycle ratios, which control the Al content in the film. Our results suggest that Al3+ ions are incorporated as substitutional or interstitial sites of the ZnO matrix. However, an addition of an excessive amount of Al content causes the formation of Al2O3 and related clusters as carrier traps opposed to electron donors, resulting in an increase in the resistivity and other associated phenomena. (C) 2013 American Vacuum Society. [http://dx.doi.org/10.1116/1.4772665]