Optical properties of β-Ga2O3 and α-Ga2O3:Co thin films grown by spray pyrolysis

Stable β-Ga2O3 and α-Ga2O3:Co thin films were grown on thoroughly cleaned borosilicate glass plates by the spray pyrolysis method. The substrate temperature during growth was maintained at 350 °C and the film was then annealed in air at 350 °C for 30 min. The optical energy gaps for these films at 295 K was given as 4.23 eV for β-Ga2O3 and 2.41 eV for α-Ga2O3:Co. The impurity absorption peaks for α-Ga2O3:Co thin film due to the transitions of 4A2(4F)→4T1(4P), 4A2(4F)→4T1(4F), and 4A2(4F)→4T2(4F) of Co2+ ions were observed at 14 925, 7142, and 4166 cm−1, with Racah parameters given as Dq=416 cm−1 and B=638 cm−1.