Influences of process temperature on the phase of Ga 2 O 3 thin films grown by atomic layer deposition (ALD) on a sapphire substrate is investigated. Ga 2 O 3 thin films grown by ALD at a process temperature of 200 C showed an amorphous phase; however, crystalline α-Ga 2 O 3 film was deposited at the deposition temperatures from 225 to 250 C. Above a process temperature of 300 C, α and β phases coexist in the grown Ga 2 O 3 thin film. Interestingly, β-Ga 2 O 3 thin film was deposited on the sapphire by an increase of working pressure during Ga 2 O 3 ALD process at the process temperature of 300 C. The bandgap of β-Ga 2 O 3 thin film was as high as~5.2 eV. A metal-semiconductor-metal type photodetector using the β-Ga 2 O 3 thin film exhibited a fast response speed with a short rise time of 1.3 μs for the detection of deep ultraviolet wavelengths.

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