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

In this study, we analyze In 2 O 3 thin-film transistors (In 2 O 3 -TFT) using synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES) in operando conditions. A bottom-gate In 2 O 3 -TFT with a high- k Al 2 O 3 gate dielectric, grown on thermally oxidized silicon (SiO 2 /p + -Si), was examined while operating at varying V GS and V 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 V DS . Furthermore, the polarity of V GS under positive V DS significantly affects the channel structure, and V 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 DSS ) arises from high intrinsic electron and defect/trap levels associated with oxygen vacancies ( V O 2+ ). Additionally, investigation beneath the Au/Ti drain and source electrodes under different bias voltages reveals substantial In 2 O 3 reduction, leading to significant indium metal (In 0 ) formation. Schematic models of carrier transport mechanisms are proposed to explain these findings.