Optimization of Erbium doping in In₂O₃ thin films using nebulized spray pyrolysis technique for room temperature ammonia sensing

Developing a fast, accurate, and room-temperature method to detect toxic gases is vital for safeguarding human lives. This study synthesizes pure In₂O₃ and In₂O₃: Er thin films (1–5 wt% Er) using nebulizer spray pyrolysis for ammonia (NH₃) gas sensing. All films showed a cubic structure of In₂O₃ with a strong (222) plane orientation. The incorporation of Er dopants led to an increase in crystallite size, and decrease in lattice strain. FESEM images revealed fine-grained structures with increase in particle size upto 4 wt% Er doping and decreases further incorporation of dopants. The bandgap was decreased from 3.46 eV to 3.24 eV at 4 wt% Er doping. Photoluminescence revealed defect states around 392 nm, 416 nm, 438 nm, 452 nm, 478 nm, and 522 nm with enhanced intensity indicating more oxygen vacancies in 4 wt% Er-doped film. The gas-sensing performance of these sensors was thoroughly examined and the results indicate that the In₂O₃: Er (4 wt%) material exhibited enhanced gas response. Notably, the In₂O₃: Er (4 wt%) film showed eighty times higher sensitivity than pure In₂O₃ at 250 ppm NH₃, along with fast response/recovery times of 13.7/6.4 s, excellent repeatability, and high selectivity. The improved performance is attributed to enhanced structural and optical properties from optimal Er doping.