Ultrahigh detectivity,high-speed and low-dark current AlGaN solar-blind heterojunction field-effect phototransistors realized using dual-float-photogating effect

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 A1_(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.