High-Sensitivity NO₂ Detection Using Se-Doped In₂O₃ Thin Films Synthesized via RF Magnetron Sputtering

Abstract

NO₂ is a key atmospheric pollutant, and its efficient detection is crucial for environmental protection and human health. Indium oxide (In₂O₃) exhibits promising gas-sensing properties owing to its wide band gap (~3.7 eV) and abundant oxygen vacancies arising from non-stoichiometry. However, poor selectivity, limited sensitivity, and high operating temperatures still hinder practical use. Here, we propose a two-step strategy: An In₂Se₃ precursor film is first deposited by RF magnetron sputtering and then oxidized at high temperature to achieve Se doping of In₂O₃. This approach introduces In-Se coordination, increases the oxygen-vacancy concentration, and generates a porous surface microstructure, thereby facilitating gas adsorption and charge transfer. The optimized Se-In₂O₃ film (1.55 at% Se) shows a 7.8-fold enhancement in NO₂ response with a detection limit of 3.3 ppb, together with excellent selectivity and 28-day stability. Spectroscopic analyses (XPS, EPR, TEM) confirm that Se doping reshapes the electronic structure and defect chemistry of In₂O₃, enabling synergistic improvements in sensitivity and response kinetics. This work highlights a scalable defect-engineering route for high-performance In₂O₃-based NO₂ sensors.