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1 Department of Electronics and Communication, B S Abdur Rahman Crescent Institute of Science and Technology, Chennai, Tamil Nadu, India – 600 048;
2 School of Mechanical Engineering, VIT University, Chennai, Tamil Nadu, India – 600 127;
3 Department of Robotics and Automation, Easwari Engineering College, Chennai, Tamil Nadu, India – 600089.
* Correspondence: msv305@yahoo.co.in
Journal of Ovonic Research 2026, 22(3),17-31; https://doi.org/10.67229/JOR16624
Indium-doped zinc oxide (In:ZnO) thin films are promising materials for NOₓ gas sensing due to their tailorable electrical properties and enhanced surface activity. In this study, ZnO thin films doped with 1–8 at% indium was deposited on glass substrates using radio-frequency magnetron sputtering to investigate the influence of dopant incorporation on structural, electrical, and NOx gas-sensing characteristics. X-ray diffraction analysis confirmed the formation of a hexagonal wurtzite ZnO structure with a preferred (002) orientation. Indium doping induced peak shifting and broadening, indicating lattice distortion caused by the substitution of In³⁺ ions without secondary phase formation. Grain size estimation using the Scherrer equation revealed an average crystallite size of ~25 nm for pure ZnO, which decreased to ~20 nm upon indium incorporation due to suppressed grain growth. Scanning Electron Microscopy (SEM) analysis revealed the surface morphology and microstructural evolution of In:ZnO thin films, indicating uniform grain distribution and enhanced crystallinity with doping concentration. Electrical resistivity strongly depended on indium percentage, with moderate doping enhancing carrier concentration, while higher doping levels led to mobility degradation due to increased scattering. Static NOₓ gas sensing measurements demonstrated significantly enhanced sensitivity for films doped with 2–6 at% indium at reduced operating temperatures, attributed to increased oxygen vacancy concentration, improved surface reactivity, and optimized microstructure. These results identify an optimal doping window and establish RF-sputtered In:ZnO thin films as efficient candidates for advanced NOₓ gas sensor applications.
