Effect of annealing temperature on bismuth oxide semiconductor thin films grown by RF sputtering at different powers

Bi₂O₃ thin films were deposited on glass substrates using RF magnetron sputtering at 80, 100, and 120 W, and the effects of post-annealing at 200 °C and 300 °C were investigated. XRD results show that all films crystallize in the monoclinic α-Bi 2 O 3 phase, with the (–112) plane becoming increasingly dominant as annealing temperature increases. Grain size increases while dislocation density and microstrain decrease with both higher sputtering power and annealing, indicating improved crystallinity. SEM analyses reveal homogeneous spherical grains in unannealed films, which transform into smoother surfaces or rod-like structures after annealing, depending on the sputtering power. EDAX confirms increased oxygen incorporation with rising annealing temperature. UV–Vis spectroscopy shows a systematic reduction in optical band gap with annealing, from 3.57 to 3.38 eV (80 W), 3.29 to 3.08 eV (100 W), and 2.88 to 2.79 eV (120 W). Overall, thermal treatment significantly enhances structural quality and tunes the optical properties of Bi 2 O 3 thin films, making them suitable for optoelectronic and sensing applications.