Saturation Mobility of 100 cm² V^–1 s^–1 in ZnO Thin-Film Transistors through Quantum Confinement by a Nanoscale In₂O₃ Interlayer Using Spray Pyrolysis

In this study, we present a comprehensive study on the fabrication and characterization of heterojunction In₂O₃/ZnO thin-film transistors (TFTs) aimed at exploiting the quantum confinement effect to enhance device performance. By systematically optimizing the thickness of the crystalline In₂O₃ (c-In₂O₃) layer to create a narrow quantum well, we observed a significant increase in saturation mobility (μ_SAT) from 12.76 to 97.37 cm² V^-1 s^-1. This enhancement, attributed to quantum confinement, was achieved through the deposition of a 3 nm c-In₂O₃ semiconductor via spray pyrolysis. Various In₂O₃ layer thicknesses (2-5 nm) were obtained by adjusting precursor solution concentration, flow rate, and number of spray cycles. Post annealing treatments were employed to reduce the defects at the interface and within the oxide film, enhancing device stability and performance. Transmission electron microscopy (TEM) confirmed the uniformity of the c-In₂O₃ film thickness, while variations in thickness significantly influenced TFT performance, particularly the turn-on voltage (<i>V</i>_GS) due to changes in the carrier concentration. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) supported the formation of a potential well with a two-dimensional electron gas (2DEG). The study of single and multiple superlattice structures of consecutive c-In₂O₃ and c-ZnO layers provided insights into the effects of multiple quantum wells on the TFT performance. This research presents an advanced approach to TFT optimization, highlighting high reliability, and environmental and bias stabilities. These lead to enhanced mobility and performance uniformity through the precise control of c-In₂O₃ layer thickness for the quantum confinement effect.