Control of grain orientation and its impact on carrier mobility in reactively sputtered Cu2O thin films

Grain orientation can be particularly important in devices such as thin film transistors (TFTs) where grain boundaries present a barrier to lateral carrier transport. This paper demonstrates that thin films of nanocrystalline cuprous oxide (Cu2O) can be grown with control of the grain orientation in the direction of either [111] or [100] perpendicular to the substrate surface using a high target utilization sputtering system. This allows a systematic study of the effect of grain orientation on the carrier mobility in Cu2O films. It is shown that the carrier mobility in as-deposited films is similar for both grain orientations while [100]-oriented thin films exhibit a higher carrier mobility for lateral conduction than films with a [111] orientation after annealing, which is discussed from the viewpoint of the Urbach energy, crystallinity and surface morphology. This experimental finding suggests that Cu2O thin films with a [100] surface grain orientation are favorable for device applications such as p-type TFTs where a high in-plane carrier mobility is desired.