Evolution of structural and photoluminescent properties of sputter-deposited Ga2O3 thin films during post-deposition heat treatment

In situ spectroscopic ellipsometry and ex situ structural investigations were performed on annealed amorphous Ga 2 O 3 thin films prepared by radio frequency sputtering . The change of the optical parameters was monitored during the annealing in air. In situ ellipsometry was shown to be a valuable method to determine the phase transition temperatures of Ga 2 O 3 during annealing in ambient conditions. X-ray diffraction and transmission electron microscopy revealed that the initially amorphous film first crystallizes into the metastable γ-Ga 2 O 3 phase, which transforms into the β-Ga 2 O 3 phase at higher temperatures. Optical transmittance measurements were used to determine the optical bandgap of the layers at the different annealing steps. Photoluminescence experiments were performed on the samples after annealing at varying temperatures and atmospheres. After the initial formation of the γ-Ga 2 O 3 phase a broad green luminescence band emerged, while after the transformation to the β-Ga 2 O 3 phase blue or red emission was observed depending on the annealing atmosphere.