High-throughput screening of phase-engineered atomically thin transition-metal dichalcogenides for van der Waals contacts at the Schottky–Mott limit

A main challenge for the development of two-dimensional devices based on atomically thin transition-metal dichalcogenides(TMDs)is the realization of metal–semiconductor junctions(MSJs)with low contact resistance and high charge transport capability.However,traditional metal–TMD junctions usually suffer from strong Fermi-level pinning(FLP)and chemical disorder at the interfaces,resulting in weak device performance and high energy consump-tion.By means of high-throughput first-principles calculations,we report an attractive solution via the formation of van der Waals(vdW)contacts between metallic and semiconducting TMDs.We apply a phase-engineering strategy to create a monolayer TMD database for achieving a wide range of work func-tions and band gaps,hence offering a large degree of freedom to construct TMD vdW MSJs with desired contact types.The Schottky barrier heights and contact types of 728 MSJs have been identified and they exhibit weak FLP(-0.62 to-0.90)as compared with the traditional metal–TMD junctions.We find that the interfacial interactions of the MSJs bring a delicate competition between the FLP strength and carrier tunneling efficiency,which can be uti-lized to screen high-performance MSJs.Based on a set of screening criteria,four potential TMD vdW MSJs(e.g.,NiTe_(2)/ZrSe_(2),NiTe_(2)/PdSe_(2),HfTe_(2)/PdTe_(2),TaSe_(2)/MoTe_(2))with Ohmic contact,weak FLP,and high carrier tunneling probability have been predicted.This work not only provides a fundamental understanding of contact properties of TMD vdW MSJs but also renders their huge potential for electronics and optoelectronics.

Van der Waals contacted WSe_(2) ambipolar transistor for in-sensor computing

Image sensors with an in-sensor computing architecture have shown great potential in meeting the energy-efficient requirements of emergent data-intensive applications,where images are processed within the photodiode arrays.It demands the composed photodiodes are reconfigurable,which are usually achieved by ambipolar two-dimensional(2D)semiconductors.To improve the ambipolar charges injection,here we report a top-gated field-effect transistor(FET)design that is of bottom van der Waals contact via transferring ambipolar 2D WSe_(2) onto Pd/Cr source/drain electrodes.The devices exhibit nearly negligible effective barrier heights for both holes and electrons based on thermionic emission mode,and show an almost balanced on/off ratio in the p-branch and n-branch.By replacing the top gate with two aligned semi-gates,the devices can effectively function as reconfigurable photodiodes.They can be switched between PIN and NIP configurations via controlling the two semi-gates,exhibiting good linearity in terms of short-circuit current(ISC)and incident light power density.The photodiode arrays are also demonstrated for in-sensor optoelectronic convolutional image processing,showing significant potential for in-sensor computing image processors.