Effects of substrate temperature on the optical and electrical properties of Al:ZnO films

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 µΩ 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.