Deep level transient spectroscopy study on defect states in In-based amorphous oxide semiconductor thin films with heterojunction diodes

Deep level transient spectroscopy (DLTS) was applied to heterojunction diodes consisting of In-Sn-Zn-O (ITZO)/p-Si to investigate the defect states in In-based amorphous oxide semiconductor thin films. The defect states located at 0.26 and 0.67 eV below the conduction band minimum (CBM) were observed in the ITZO. After thermal annealing at 250 °C, two defect states at 0.22 and 0.28 eV were identified from the Arrhenius plots of time constants, while the defect states were not detected around 0.5-0.7 eV. The origins of the defects are not clear at present; however, the performance of TFTs is definitely governed by the defect states. It is shown that DLTS with heterojunction diodes give a useful insight for developing high electron mobility amorphous oxide semiconductors.