  This paper addresses the effect of disorder on the carrier transport
mechanism of atomic layer deposited ZnO thin films as has been investigated by
temperature dependent electrical resistivity measurements in the temperature
range of 4.2K to 300K. Films were grown on (0001) sapphire substrate at
different substrate temperatures varying from 150 to 350 C. The defects and
structural disorder in the films were found to be strongly dependent on their
growth temperature. The films grown at 150, 300 and 350 C were found to be
semiconductor-like in the whole measurement temperature range of resistivity
due to the enhanced disorder in these films. However, a metal to semiconductor
transition (MST) at low temperature has been observed in the films grown at 200
and 250 C. It was also observed that the film grown at 250 C with higher
residual resistivity, the transition temperature shifted towards the higher
value due to the increased disorder in this film as compared to that grown at
200 C. The upturn in resistivity below the transition temperature has been well
explained by considering quantum corrections to the Boltzmanns conductivity
which includes the effect of weak localization and coulomb electron-electron
interactions related to the existence of disorder in these films.
