AlGaN solar-blind phototransistor capable of directly detecting sub-fW signals:self-depletion and photorecovery of full-channel 2DEG enabled by a quasi-pseudomorphic structure

Heterojunction field-effect phototransistors using two-dimensional electron gas(2DEG)for carrier transport have great potential in photodetection owing to its large internal gain.A vital factor in this device architecture is the depletion and recovery of the 2DEG under darkness and illumination.This is usually achieved by adding an external gate,which not only increases the complexity of the fabrication and the electrical connection but also has difficulty ensuring low dark current(I_(dark)).Herein,a quasi-pseudomorphic AlGaN heterostructure is proposed to realize the self-depletion and photorecovery of the 2DEG,in which both the barrier and the channel layers are compressively strained,making the piezoelectric and spontaneous polarization reverse,thus depleting the 2DEG and tilting the entire barrier and channel band to form two built-in photogates.The fabricated solar-blind phototransistors exhibit a very low I_(dark)below 7.1×10^(-10)mA∕mm,a superhigh responsivity(R)of 2.9×10^(9)A∕W,a record high detectivity(D^(*))of 4.5×10^(21)Jones,and an ultrafast response speed at the nanosecond level.The high performance is attributed to the efficient depletion and recovery of the full 2DEG channel by the two photogates,enabling direct detection of the sub-fW signal.This work provides a simple,effective,and easily integrated architecture for carrier control and supersensitive photodetection based on polarization semiconductors.

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.