Al-doped ZnO films were grown on glass substrates by the pulsed-laser deposition technique with varying substrate temperatures. The optical band gap decreases from 3.64 to 3.46 eV as the substrate temperature increases from 350 to 450 • C, illustrating the increase in Al content in the context of a degenerate semiconductor, and can be explained in the framework of the Burstein-Moss effect. All films show optical transparency greater than 85%. Al:ZnO films show a metal-semiconductor transition to metal-like behavior as the substrate temperature increases from 350 to 450 • C. The observed metal-like and metal-semiconductor transitions are explained by taking into account the Mott phase transition and localization effects due to defects. The resistivity decreases from 896 to 470 µ cm as the substrate temperature increases from 350 to 450 • C. In addition, the competition between the thermally activated carriers and scattering effects of free carriers in a degenerate semiconductor can also explain the metal-semiconductor transition.
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