Quantum Confinement and Thickness‐Dependent Electron Transport in Solution‐Processed In₂O₃ Transistors

The dependence of charge carrier mobility on semiconductor channel thickness in field‐effect transistors is a universal phenomenon that has been studied extensively for various families of materials. Surprisingly, analogous studies involving metal oxide semiconductors are relatively scarce. Here, spray‐deposited In₂O₃ layers are employed as the model semiconductor system to study the impact of layer thickness on quantum confinement and electron transport along the transistor channel. The results reveal an exponential increase of the in‐plane electron mobility (µ_e) with increasing In₂O₃ thickness up to ≈10 nm, beyond which it plateaus at a maximum value of ≈35 cm² V⁻¹ s⁻¹. Optical spectroscopy measurements performed on In₂O₃ layers reveal the emergence of quantum confinement for thickness <10 nm, which coincides with the thickness that µ_e starts deteriorating. By combining two‐ and four‐probe field‐effect mobility measurements with high‐resolution atomic force microscopy, it is shown that the reduction in µ_e is attributed primarily to surface scattering. The study provides important guidelines for the design of next generation metal oxide thin‐film transistors.