Mapping the nanoscale effects of charge traps on electrical transport in grain structures of indium tin oxide thin films

Abstract

We report the mapping of the nanoscale effects of charge trap activities in the grain structures of an oxygen plasma-treated indium tin oxide (ITO) thin film. Here, a conducting Pt probe made direct contact with the surface of an ITO thin film and scanned the surface while measuring the maps of electrical currents and noises. The measured data were analyzed to obtain the maps of sheet conductance (G_s) and charge trap density (N_eff) in the grain structures of the ITO thin film. The results showed that grain boundaries exhibited a lower sheet conductance and a higher charge trap density than those of the regions inside grains. Interestingly, the scaling behavior of G_s ∝ N_eff^−0.5 was observed in both grain and boundary regions, indicating diffusive charge transport. Furthermore, the sheet conductance increased by two times, and the density of charge traps decreased by ∼70% after an oxygen plasma treatment, presumably due to the enhanced crystallinity of the ITO film. Interestingly, in some boundary regions, the sheet conductance and the charge trap density exhibited the scaling behavior of G_s ∝ N_eff^0.5, which was attributed to the hopping conduction caused by the enhanced crystallinity and increased localized states in the boundary regions. Since our method provides valuable insights into charge transport and charge trap activities in transparent conducting thin films, it can be a powerful tool for basic research and practical optoelectronic device applications based on ITO thin films.