Metal–Semiconductor–Metal ε-Ga₂O₃ Solar-Blind Photodetectors with a Record-High Responsivity Rejection Ratio and Their Gain Mechanism

In recent years, Ga 2 O 3 solar-blind photodetectors (SBPDs) have received great attention for their potential applications in solar-blind imaging, deep space exploration, confidential space communication, etc. In this work, we demonstrated an ultra-high-performance ε-Ga 2 O 3 metal–semiconductor–metal (MSM) SBPD. The fabricated photodetectors exhibited a record-high responsivity and fast decay time of 230 A/W and 24 ms, respectively, compared with MSM-structured Ga 2 O 3 photodetectors reported to date. Additionally, the ε-Ga 2 O 3 MSM SBPD presents an ultrahigh detectivity of 1.2 × 10 15 Jones with a low dark current of 23.5 pA under an operation voltage of 6 V, suggesting its strong capability of detecting an ultraweak signal. The high sensitivity and wavelength selectivity of the photodetector were further confirmed by the record-high responsivity rejection ratio ( R 250 nm / R 400 nm ) of 1.2 × 10 5 . From the temperature-dependent electrical characteristics in the dark, the thermionic field emission and Poole–Frenkel emission were found to be responsible for the current transport in the low and high electric field regimes, respectively. In addition, the gain mechanism was revealed by the Schottky barrier lowering effect due to the defect states at the interface of the metal contact and Ga 2 O 3 or in the bulk of Ga 2 O 3 based on current transport mechanism and density functional theory calculations. These results facilitate a better understanding of ε-Ga 2 O 3 photoelectronic devices and provide possible guidance for promoting their performance in future solar-blind detection applications.