Dual-path gain in Si-based ZnGa2O4 MOSFET solar-blind ultraviolet phototransistors

Solar-blind ultraviolet (UV) photodetection on silicon platforms is an important step toward practical optoelectronic integration. Here, we demonstrate a bottom-gate ZnGa2O4 metal-oxide-semiconductor field-effect transistor (MOSFET) solar-blind UV photodetector on a Si substrate with a Si3N4 gate dielectric. The device exhibits n-channel enhancement-mode operation with an on/off current ratio of ∼108 and a picoampere-level off-state current. Under solar-blind UV illumination, the phototransistor achieves a peak responsivity of 1.09 × 103 A/W, a detectivity of 1.74 × 1013 Jones, a UV-to-visible rejection ratio of 2.6 × 105, and rise/decay times of 22.7/19.2 ms. The photo-induced shift in the capacitance–voltage characteristics suggests the participation of charge trapping at the Si3N4/ZnGa2O4 interface, while cathodoluminescence and electrical analyses identify compensating zinc vacancy (VZn) acceptor defects coexisting with Ga-on-Zn (GaZn) antisite donors within the ZnGa2O4 channel. These trap states sustain two parallel gain pathways within the MOSFET architecture: vertical threshold-voltage modulation amplified through the subthreshold characteristic, and lateral photoconductive gain arising from carrier lifetime extension via hole capture by VZn acceptor defects. By distributing the total gain across two amplification channels rather than relying on prolonged carrier lifetime alone, this architecture offers a route to balanced high-gain and fast-response solar-blind UV detection on Si platforms compatible with CMOS technology.