Control of grain orientation and its impact on carrier mobility in reactively sputtered Cu<inf>2</inf>O thin films

Abstract

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.