Quantitative Insight of Annealing Atmosphere-Induced Device Performance and Bias Stability in a Ga-Doped InZnSnO Thin-Film Transistors

This study aimed to determine the origin of postannealing atmosphere-induced device performance and bias stability of Ga-doped InZnSnO (IGZTO)-based thin-film transistors (TFTs) by quantitative analysis of defect states. IGZTOs annealed in the presence of oxygen (x%-IGZTO) exhibited excellent switching properties, but IGZTOs annealed without oxygen (0%-IGZTO) had insufficient switching properties with a high and constant drain current. Quantitative defect analysis using photograph-induced current transient spectroscopy (PICTS) revealed that the improved switching performance for the x%-IGZTO TFTs was due to the significant decrease in oxygen-related defect densities: from 4.19 × 1018 #/cm-3 for 0%-IGZTO to 8.71 × 1017 and 2.97 × 1017 #/cm-3 for x%-IGZTOs annealed in the presence of 20% and 50% oxygen, respectively. The x%-IGZTOs demonstrated superior stability under positive bias stress (PBS) than under negative bias stress (NBS), which was attributable to the low shallow-level and high deep-level defect states, respectively. Furthermore, the 20%-IGZTO exhibited excellent bias stability compared with the 50%-IGZTO under both PBS and NBS. This was ascribed to the increase in shallow and deep level defects by 7% and 18% as oxygen content increased from 20% to 50%, respectively. These quantitative findings were strongly supported by qualitative defect analysis results from X-ray photoelectron spectroscopy (XPS) and spectroscopic ellipsometry. Quantitatively analyzing defects in TFTs can help us grasp the behavior of semiconductor devices at the molecular level and design novel high-performance electronic devices.