Study on the defects in metal–organic chemical vapor deposited zinc tin oxide thin films using negative bias illumination stability analysis

This study experimentally examined the physical and electrical characteristics of ZnxSnyOz (ZTO) thin films grown by a metal–organic chemical vapor deposition (MOCVD) method with various Zn/Sn atomic compositions. The corresponding defect structures of the deposited films were investigated in detail using negative bias illumination stability (NBIS) analysis in the thin film transistor (TFT) structure. The ZTO thin films were deposited at a substrate temperature of 400 °C and post-deposition annealed at 600 °C, which still resulted in the amorphous structure except for the Sn-rich film where a nano-crystalline SnO2 phase is detected. Among the films with different Zn/Sn atomic compositions, the film with a Zn/Sn atomic composition of ∼50/50 showed the best electrical performance. After applying NBIS stress for 1000 s, the transfer curves of the Zn-rich ZTO TFT showed a hump, but the transfer curves of the Sn-rich ZTO TFT exhibited a parallel shift to the negative bias direction. These phenomena were attributed to the difference in the oxygen vacancy energy states generated in the ZTO band gap by light illumination. The Zn- and Sn-related oxygen vacancies generated deep donor like trap states at ∼0.3 eV and shallow states at ∼0.1 eV from the conduction band (or mobility) edge, respectively, which were identified by the quantitative simulations of the transfer curves of the TFTs.