100 mV Ultra-Low Bias AlGaN/GaN Photodetector Based on Fin-Shaped Capacitor Configuration for Future Integrated Optoelectronics

This study presents an AlGaN/GaN ultraviolet (UV) photodetector proven to be highly effective when working under an ultra-low bias voltage. The proposed photodetector is based on an innovative configuration consisting of repetitive AlGaN/GaN fin-shaped capacitor units, which make use of the two-dimensional electron gas (2DEG) layer as the positive field plates and the sidewall tungsten Schottky metal as the ground plates to surround the bulk of photocarrier generation space. Furthermore, a unique partial sidewall oxide structure is fabricated to partition the 2DEG field plates from the ground plates and to enable proper depletion field formation. With the special structure design, the symmetrical three-dimensional depletion fields are formed within each fin-shaped capacitor unit to spatially pinch off the entire bulk region at an ultra-low bias voltage. Effective photocarrier collection can then be achieved by such an extensive field coverage. When biased at 100 mV, intriguing performances in response to 365 nm UV were demonstrated by the fabricated prototype, such as a photocurrent-to-dark-current-ratio of 7.0 × 104, a peak responsivity of 1.1 × 103 A/W, as well as a large detectivity of 1.1 × 1016 Jones. Good transient performance was also observed under 365 nm UV pulses of 0.7 mW/cm2 in intensity with an operating frequency of up to 1 kHz. This work embodies an ultra-low voltage UV photodetector on the AlGaN/GaN epitaxy heterojunction platform with concise and complementary metal-oxide-semiconductor (CMOS)-compatible fabrication procedures, opening up an appealing potential in ultra-low-power optoelectronic integrated circuits for future Internet of Things and edge computing applications.