Optical and luminescent properties of undoped and rare-earth-doped Ga2O3thin films deposited by spray pyrolysis

Spray pyrolysis was used to prepare polycrystalline thin films of undoped Ga 2 O 3 , as well as those doped separately with Eu 3+ , Tb 3+ and Tm 3+ . The energy gap values of the as-grown films and those annealed at 600{}C and 900{}C were found to be 4.75, 4.48 and 4.44 eV, respectively. Films containing Eu 3+ and Tb 3+ exhibited red and green cathodoluminescence (CL), respectively. The CL of Ga 2 O 3 : Tm mainly showed a broad band in the blue-green region, which resulted from the emission by both the Ga 2 O 3 host and Tm 3+ . The broad blue-green emission band was divided into three Gaussian peaks at 424 nm (2.92 eV), 497 nm (2.49 eV) and 526 nm (2.36 eV). The CL intensity of undoped Ga 2 O 3 thin films depended on the annealing ambient and temperature, suggesting that it is associated with the presence of oxygen vacancies. Mechanisms responsible for the broad blue-green emission of undoped Ga 2 O 3 thin films were explored.