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초록

Understanding how compositional variations control defect formation is crucial to advancing amorphous oxide semiconductor thin‑film transistors (TFTs). This study quantitatively investigates defect states in binary (In2O3, Ga2O3, ZnO), ternary (InGaO, InZnO, GaZnO), and quaternary (a‑IGZO) systems using photo‑induced current transient spectroscopy (PICTS). Binary oxides such as In2O3 and ZnO predominantly generate shallow donor‑like defects near the conduction band, whereas Ga2O3 suppresses these defects and introduces deeper trap levels. These tendencies extend into the ternary and quaternary systems, where defect densities increase in the order: In‑rich > Zn‑rich > Ga‑rich TFTs. Furthermore, composition‑dependent shifts in activation energy of the defects were observed. Notably, quaternary a‑IGZO exhibits a new deep defect at ∼1.80 eV, absent in the simpler binary and ternary systems, which highlights the intrinsic complexity of multi‑cation amorphous networks. These defect characteristics strongly influence the electrical performance of the TFTs. In‑rich a‑IGZO exhibits high mobility (μFE) and low threshold voltage (VTH) driven by abundant shallow donors and strong In‑5 s orbital overlap. In contrast, Ga‑rich compositions show reduced μFE and increased VTH due to suppressed oxygen‑vacancy‑related donors and weak Ga-5s orbital overlap. In‑rich TFTs remain stable under positive bias stress but degrade under negative bias stress, whereas Ga‑rich TFTs display the opposite behavior. Meanwhile, Zn-rich a-IGZO showed intermediate electrical and bias stress stability behavior, bridging the two extremes. Overall, this study establishes a quantitative, composition‑defect–performance framework essential for the rational design of high‑performance and reliable oxide TFTs. © 2026

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