Study of Local Band Bending in <i>n</i>-Channel In₂O₃ Thin-Film Transistors under Gate and Drain Voltage Stress Using <i>Operando</i> Hard X-ray Photoelectron Spectroscopy

In this study, we analyze In₂O₃ thin-film transistors (In₂O₃-TFT) using synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES) in <i>operando</i> conditions. A bottom-gate In₂O₃-TFT with a high-<i>k</i> Al₂O₃ gate dielectric, grown on thermally oxidized silicon (SiO₂/p⁺-Si), was examined while operating at varying <i>V</i>_GS and <i>V</i>_DS. The results reveal that the In 3d core level binding energy varies along the horizontal channel length, driven by the potential gradient induced by <i>V</i>_DS. Furthermore, the polarity of <i>V</i>_GS under positive <i>V</i>_DS significantly affects the channel structure, and <i>V</i>_DS influences the vertical electrostatic potential in the buried gate dielectric and the gate electrode. Analysis suggests that the primary source of drain-source leakage current (<i>I</i>_DSS) arises from high intrinsic electron and defect/trap levels associated with oxygen vacancies (<i>V</i>_O²⁺). Additionally, investigation beneath the Au/Ti drain and source electrodes under different bias voltages reveals substantial In₂O₃ reduction, leading to significant indium metal (In⁰) formation. Schematic models of carrier transport mechanisms are proposed to explain these findings.