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β-Ga2O3 epitaxial thin films were deposited using laser molecular beam epitaxy technique and oxygen atmosphere in situ annealed in order to reduce the oxygen vacancy. Metal/semiconductor/metal structured photodetectors were fabricated using as-grown film and annealed film separately. Au/Ti electrodes were Ohmic contact with the as-grown films and Schottky contact with the annealed films. In compare with the Ohmic-type photodetector, the Schottky-type photodetector takes on lower dark current, higher photoresponse, and shorter switching time, which benefit from Schottky barrier controlling electron transport and the quantity of photogenerated carriers trapped by oxygen vacancy significant decreasing.

A solar-blind photodetector based on β-GaO/NSTO (NSTO = Nb:SrTiO) heterojunctions were fabricated for the first time, and its photoelectric properties were investigated. The device presents a typical positive rectification in the dark, while under 254 nm UV light illumination, it shows a negative rectification, which might be caused by the generation of photoinduced electron-hole pairs in the β-GaO film layer. With zero bias, that is, zero power consumption, the photodetector shows a fast photoresponse time (decay time τ = 0.07 s) and the ratio I/I ≈ 20 under 254 nm light illumination with a light intensity of 45 μW/cm. Such behaviors are attributed to the separation of photogenerated electron-hole pairs driven by the built-in electric field in the depletion region of β-GaO and the NSTO interface, and the subsequent transport toward corresponding electrodes. The photocurrent increases linearly with increasing the light intensity and applied bias, while the response time decreases with the increase of the light intensity. Under -10 V bias and 45 μW/cm of 254 nm light illumination, the photodetector exhibits a responsivity R of 43.31 A/W and an external quantum efficiency of 2.1 × 10 %. The photo-to-electric conversion mechanism in the β-GaO/NSTO heterojunction photodetector is explained in detail by energy band diagrams. The results strongly suggest that a photodetector based on β-GaO thin-film heterojunction structure can be practically used to detect weak solar-blind signals because of its high photoconductive gain.

A self-powered ultraviolet photodetector with an extremely high responsivity (54.43 mA W−1) was fabricated by constructing p–n junction of GaN/Ga2O3 films.

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