Preparation And Principle Analysis For High-Performance GaAs-based Nanowire Photodetectors

With high optical sensitivity and large light absorption,nanostructure photodetectors have the advantages of fast response and high photoelectric conversion efficiency.They can be applied to optical imaging and sensing,environmental monitoring,chemical/bio sensing,and rocket plume detection.As a typical ?-? compound semiconductor material,GaAs nanowires(NWs),with direct bandgap(1.42 eV)and high electron mobility,is a potential material for achieving high-speed infrared photodetectors at room temperature.However,the rich surface states of GaAs NWs usually generate surface currents and leading to an increase in the dark current.Besides,an increase in the photo-generated carrier recombination rate is also caused by the high surface state density,resulting in a decrease in the photocurrent.It is not benefit for the preparation of high-performance GaAs-based NWs photodetectors.The aim of this paper is reducing the dark current and increasing the photocurrent of GaAs NW photodetectors,to realize high performance GaAs-based NW photodetectors.The main results obtained are as follows:(1)The effect and principle analysis of sulfur passivation on the performance of GaAs NW photodetectors.NWs photodetectors,which have the advantages of fast response and high photoelectric conversion efficiency,can be widely applied in various industries.However,the rich surface states will result in large dark current and can hinder the development of high-performance nanowire photodetectors.In this paper,the influence and mechanism of sulfur surface passivation on the dark current of single GaAs NW photodetector have been studied.The dark current is significantly reduced by about 30 times after surface passivation.We confirm that the origin of the reduction for dark current is the decrease of the surface state density.As a result,a single GaAs NW photodetector with the low dark current of 7.18×10^-2 pA,the high detectivity of 9.04×10¹² cm·H^0.5·W^-1 have been achieved.(2)The effect and principle analysis of doping on the performance of GaAs NW photodetectors.Metal-semiconductor-metal(MSM)-structured GaAs-based NWs photodetectors have been widely reported due to their promises as an alternative for high-performance devices.Owing to the Schottky built-in electric fields in the MSM structure photodetectors,enhancements in photoresponsivity can be realized.Thus,strengthen the built-in electric field is an efficacious way to make the detection capability better.In this study,we fabricate a single GaAs NW MSM photodetector with superior performance by doping-adjusting the Fermi level to strengthen the built-in electric field.An outstanding responsivity of 1175A/W is obtained.This is two orders of magnitude better than the responsivity of the undoped sample.Scanning photocurrent mappings and simulations are performed to confirm that the enhancement in responsivity is because of the increase in the hole Schottky built-in electric field,which can separate and collect the photogenerated carriers more effectively.(3)Design and performance analysis of GaAs-based NW APD.NW avalanche photodiodes(APDs)have potential applications in the fields of single-photon detection owing to their advantage of superior gain and detection efficiency.Although many efforts have been made in past years,the performances of nanowire APDs are still limited.Here,we demonstrate a high-performance separate absorption and multiplication avalanche photodiode(SAM-APD)by inserting barrier layer into the interface between absorption and multiplication region acted as holes well to enhance the electric field of multiplication region.In particular,this device presents a high responsivity of 3.35×10³ A/W and a multiplication factor of 10⁴ for 940 nm laser at 18 V.Its detectivity is as high as 2.51×10¹²cm·H^0.5·W^-1,which is comparable to that of commercial InGaAs APD(10¹²cm·H^0.5·W^-1).The role of the insert layer in APD is confirmed through detailed experimental results and theoretical simulations.In addition,this SAM-APD device has low noise currents,and the 1/f noise is dominated owing to the large surface area-volume ratio in the NW.(4)High responsivity self-powered GaAs NW-WSe₂ heterojunction photodetector.Integrated mixed-dimensional(MD)van der Waals(vdWs)heterojunctions for self-powered photodetectors have attracted intense attention.Performances of these photodetectors are highly dependent on the interface properties,including the semiconductor-metal interface and the semiconductor-semiconductor interface.To date,how to balance the interface properties still remains to be explored.Here,we explore a straightforward strategy to balance the interface properties in the MD-vdWs heterojunction photodetector,by tuning the Fermi level of ambipolar two-dimensional(2D)material with a gate bias.The effectiveness of gate-tunable interface properties is verified by a GaAs-WSe₂MD vdWs heterojunction self-powered photodetector with different metal contacts.Under the gate biasing,the responsivity is enhanced from 1.23×10² mA/W to 5.11×10² mA/W in the GaAs-WSe₂ heterojunction photodetector with the Au/Cr electrodes,which is better than the state-of-the-art GaAs-based self-powered photodetectors.The contents of this paper are of great significance for achieving high-performance GaAs-based NWs and other low-dimensional material photodetectors,and promoting the further application of these materials.