Dramatic reduction in dark current of β-Ga ₂O ₃ ultraviolet photodectors via β-(Al _0.25Ga _0.75) ₂O ₃ surface passivation

Solar-blind ultraviolet photodetectors with metal-semiconductor-metal structure were fabricated based on β-(Al _0.25Ga _0.75)x ₂O ₃/ β-Ga ₂O ₃ film grown by metal-organic chemical vapor deposition. It was known that various surface states increase dark current and a large number of defects can hinder the transport of carriers, resulting in low switching ratio and low responsivity of the device. In this work, β-(Al _0.25Ga _0.75) ₂O ₃ films are used as surface passivation materials. Owning to its wide band gap, we obtain excellent light transmission and high lattice matching with β-Ga ₂O ₃. We explore the change and mechanism of the detection performance of the β-Ga ₂O ₃ detector after β-(Al _0.25Ga _0.75) ₂O ₃ surface passivation. It is found that under the illumination with 254 nm light at bias 5 V, the β-(Al _0.25Ga _0.75) ₂O ₃/ β-Ga ₂O ₃ photodetectors show dark current of just 18 pA and high current on/off ratio of 2.16 × 10 ⁵. The dark current is sharply reduced about 50 times after passivation of the β-Ga ₂O ₃ surface, and current on/off ratio increases by approximately 2 times. It is obvious that β-Ga ₂O ₃ detectors with β-(Al _0.25Ga _0.75) ₂O ₃ surface passivation can offer superior detector performance.