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.

Ultrasensitive and high-speed AlGaN/AlN solarblind ultraviolet photodetector:a full-channelself-depleted phototransistor by a virtual photogate

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-Al Ga N/Al N phototransistor with a self-depleted full channel is reported.The self-depletion of the highly conductive n-Al Ga N 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/3.1μs,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~p A 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.