Performance enhancement of AlGaN solar-blind field effect phototransistors via additional surface Schottky gate

This work presents an AlGaN-based solar-blind field-effect phototransistor (FEPT) featuring a dual-gate structure that combines a surface Schottky gate with a built-in polarization photogate. By introducing an additional Pt Schottky gate on the FEPT, dark current leakage and photo-response instability caused by the surface states can be effectively suppressed. As a result, the FEPT with an additional Pt Schottky gate exhibits an ultralow dark current of 5.86×10⁻¹⁴ A at 10 V, which is five orders of magnitude lower than that of the device without surface Pt gate. Correspondingly, the shot-noise-limited specific detectivity is promoted by two orders of magnitude, reaching 1.65×10¹⁷ Jones at 10 V bias. Furthermore, the improved device shows much more stable photo-responses and a rapider dark current recovery in the periodic illumination tests, exhibiting a significantly weakened persistent photoconductivity effect. These performance improvements with surface Pt gate suggest a significant potential in the practical applications requiring high sensitivity, high repeatability and high speed. Moreover, the demonstrated shielding effect of the surface Schottky gate on the surface states also provide a valuable insight into the suppression of defect effects in the planar devices.