Charge injection in ultrathin IGO TFTs controlled by a tradeoff between work function and interfacial oxidation enthalpy

Understanding the metal/semiconductor contact is crucial for ultrathin oxide thin-film transistors (TFTs), where the interfacial region becomes comparable to the conductive channel. Here, we investigate three metal electrodes (Ti, Cu, and Al) interfaced with atomic layer-deposited 7 nm indium gallium oxide. X-ray photoelectron spectroscopy depth profiling and ultraviolet photoelectron spectroscopy analysis indicate that the contact behavior is predominantly governed by the reaction pathway and the reversibility of interfacial oxygen redox chemistry, rather than by work-function matching alone. Al undergoes rapid self-oxidation to form a dense Al2O3 barrier that suppresses diffusion and leads to large contact resistance. Ti follows a redox-driven pathway governed by its standard oxide formation enthalpy, which induces strong oxygen extraction and forms an In0-rich, highly conductive interfacial region yielding the highest mobility (74.9 cm2 V−1 s−1). In contrast, Cu drives substitutional solid-solution formation, achieving the lowest contact resistance (22.6 Ω cm) and best thermal stability. These results support a reaction-pathway-guided principle for the electrode selection in ultrathin oxide TFTs, revealing the dominant role of oxygen coordination chemistry in nanoscale contact engineering.