Analysis of subthreshold photo-leakage current in ZnO thin-film transistors using indium-ion implantation

Mechanism of photo-leakage current in the ZnO TFTs has been analyzed by comparison between the light irradiated TFTs and indium (In) ion implanted TFTs where the selected areas of the channel region were irradiated or implanted. In case of the TFT with In ion implantation at a source region, the positive charge of ionized donors at the source region lowered the potential barrier at the source electrode and increased leakage current even at a dark condition due to carrier injection from the source into the channel region. In case of light irradiation of the ZnO TFT, similar phenomenon was observed due to the hole accumulation at the source region. From the analogy of the leakage properties, it is confirmed that the photo-leakage current is mainly due to the accumulation of holes near the source electrode, which lowers the potential barrier for the carrier injection from the source to the channel region, contributing to the generation of the leakage current.