High doping efficiency of the Mg dopant in Al-rich AlGaN is highly desired for AlGaN based deep ultraviolet optoelectronics.

High detectivity is essential for solar-blind deep-ultraviolet (DUV) light detection because the DUV signal is extremely weak in most applications. In this work, we report ultrahigh-detectivity AlGaN-based solar-blind heterojunction-field-effect phototransistors fabricated utilizing dual-float-photogating effect. The p + - Al 0.4 GaN layer and Al 0.4 GaN absorber layer deposited on the Al 0.6 GaN barrier serve as top pin-junction photogate, while the thin Al 0.4 GaN channel layer with a strong polarization field inside acts as virtual back photogate. Due to the effective depletion of the two-dimensional electron gas at the Al 0.6 Ga 0.4 N / Al 0.4 Ga 0.6 N heterointerface by the top photogate, the dark current was suppressed below 2 pA in the bias range of 0 to 10 V. A high photo-to-dark current ratio over 10 8 and an optical gain of 7.5 × 10 4 were demonstrated at a bias of 5 V. Theoretical analysis indicates that the optical gain can be attributed to the joint action of the floating top and back photogates on the channel current. As a result, a record high flicker noise (Johnson and shot noise) limited specific detectivity of 2.84 × 10 15 ( 2.91 × 10 17 )    cm   Hz 0.5   W − 1 was obtained. Furthermore, high response speed at the microsecond level was also shown in the devices. This work provides a promising and feasible approach for high-sensitivity DUV detection.

High sensitivity, high solar rejection ratio, and fast response are essential characteristics for most practical applications of solar-blind ultraviolet (UV) detectors. These features, however, usually require a complex device structure, complicated process, and high operating voltage. Herein, a simply structured n-AlGaN/AlN phototransistor with a self-depleted full channel is reported. The self-depletion of the highly conductive n-AlGaN channel is achieved by exploiting the strong polarization-induced electric field therein to act as a virtual photogate. The resulting two-terminal detectors with interdigital Ohmic electrodes exhibit an ultrahigh gain of 1.3 × 10 5 , an ultrafast response speed with rise/decay times of 537.5 ps/3.1 μs, and an ultrahigh Johnson and shot noise (flicker noise) limited specific detectivity of 1.5 × 10 18 ( 4.7 × 10 16 ) Jones at 20-V bias. Also, a very low dark current of the order of ∼ pA and a photo-to-dark current ratio of above 10 8 are obtained, due to the complete depletion of the n - Al 0.5 Ga 0.5 N channel layer and the high optical gain. The proposed planar phototransistor combines fabrication simplicity and performance advantages, and thus is promising in a variety of UV detection applications.

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