Synergistic dual-polarization-photogated AlGaN heterojunction phototransistor for ultrafast solar-blind ultraviolet detection

Overcoming the persistent photoconductivity (PPC) effect in AlGaN-based heterojunction phototransistors without compromising gain and spectral selectivity remains a critical challenge for solar-blind ultraviolet (SBUV) detection. Herein, we present a two-terminal phototransistor that utilizes intrinsic negative polarization charges at dual heterointerfaces (top: Al0.44GaN/Al0.56GaN; back: Al0.44GaN/AlN) to achieve synergistic top/back-gate-like control, eliminating conventional p-doping or third-terminal gates. The resulting superimposed vertical electric fields (>1 MV/cm) simultaneously enable: (1) complete channel depletion (92 pA dark current at 5 V), (2) trap-state carrier release, and (3) PPC suppression. The phototransistor demonstrates ultrafast response (rise/fall time = 1.74 ns/3.42 μs) while maintaining high gain (∼104), outstanding specific detectivity (2.08 × 1015 Jones) and excellent 272/300 nm spectral rejection ratio (5.1 × 104). This dual-polarization-gate approach offers a defect-resistant solution for high-performance SBUV photodetection, especially for encrypted UV communication applications.