High-Temperature Superconducting YBa_(2)Cu_(3)O_(7-δ)Josephson Junction Fabricated with a Focused Helium Ion Beam

As a newly developed method for fabricating Josephson junctions,a focused helium ion beam has the advantage of producing reliable and reproducible junctions.We fabricated Josephson junctions with a focused helium ion beam on our 50 nm YBa_(2)Cu_(3)O_(7-δ)(YBCO)thin films.We focused on the junction with irradiation doses ranging from 100 to 300 ions/nm and demonstrated that the junction barrier can be modulated by the ion dose and that within this dose range,the junctions behave like superconductor–normal conductor–superconductor junctions.The measurements of the I–V characteristics,Fraunhofer diffraction pattern,and Shapiro steps of the junctions clearly show AC and DC Josephson effects.Our findings demonstrate high reproducibility of junction fabrication using a focused helium ion beam and suggest that commercial devices based on this nanotechnology could operate at liquid nitrogen temperatures.

High gain,broadband p-WSe_(2)/n-Ge van der Waals heterojunction phototransistor with a Schottky barrier collector

Mixed-dimensional van der Waals(vdW)heterostructures based on two-dimensional transition metal dichalcogenides and threedimensional semiconductors have led to a new era in next-generation optoelectronics due to the high-quality interfaces and energy band complementation,especially in broadband photodetectors which can be used for all-weather navigation,object identification,etc.However,the reported photodetectors conventionally operated in photodiode mode with low responsivity and a narrow response spectrum.In this study,we report a p-WSe_(2)/n-Ge vdW heterojunction phototransistor with a Schottky barrier collector on n-Ge for broadband photodetection.Large hole/electron injection ratio from p-WSe_(2)/n-Ge heterojunction under forward bias due to their large bandgap offset renders the high photocurrent gain,while the Ge Schottky barrier limits the dark current.The responsivities of the phototransistor at 1.0 V emitter-collector bias are 55,95,and 120 A·W−1 at 405,1,310,and 1,550 nm,respectively,which is superior to that of the corresponding p-WSe_(2)/n-Ge photodiodes.The phototransistor shows a high photocurrent gain of 80,a specific detectivity of 1011 Jones,as well as a fast response time of 290μs at 1,550 nm.The results suggest that the novel phototransistor being implemented with complementary metal-oxide-semiconductor processing is an ideal strategy for high-performance broadband photodetection.