Abstract
A series of zinc stannate (Zn2SnO4) thin films were prepared at four different substrate temperatures; namely, room-temperature (25 degrees C), 50 degrees C, 100 degrees C and 200 degrees C. Direct-current resistivity measurements were performed on these samples in the temperature range from room temperature (similar to 290 K) up to about 500 K. A phase transition (of positive temperature coefficient (PTC) of resistance) was observed in the thin film grown at room temperature at about 385 K. Other investigated samples showed a semiconducting behaviour of three distinct conduction mechanisms extending from intrinsic to thermal freeze-out conduction. The width of the band gap E-g was found to depend on the substrate temperature and was discussed in terms of a formation of a band tailing. Thermal freeze-out was dominant at the lower temperature region.