Characterization of vertical Au/β -Ga₂O₃ single-crystal Schottky photodiodes with MBE-grown high-resistivity epitaxial layer

High-resistivity β -Ga₂O₃ thin films were grown on Si-doped n-type conductive β -Ga₂O₃ single crystals by molecular beam epitaxy (MBE). Vertical-type Schottky diodes were fabricated, and the electrical properties of the Schottky diodes were studied in this letter. The ideality factor and the series resistance of the Schottky diodes were estimated to be about 1.4 and 4.6× 10⁶ Ω . The ionized donor concentration and the spreading voltage in the Schottky diodes region are about 4× 10¹⁸ cm^-3 and 7.6 V, respectively. The ultra-violet (UV) photo-sensitivity of the Schottky diodes was demonstrated by a low-pressure mercury lamp illumination. A photoresponsivity of 1.8 A/W and an external quantum efficiency of 8.7× 10²% were observed at forward bias voltage of 3.8 V, the proper driving voltage of read-out integrated circuit for UV camera. The gain of the Schottky diode was attributed to the existence of a potential barrier in the i-n junction between the MBE-grown highly resistive β -Ga₂O₃ thin films and the n-type conductive β -Ga₂O₃ single-crystal substrate.