Current Rectification in a Sub-2 nm CNT/V-Doped WS2/MoS2/CNT Vertical Monolayer P-N Diode.

Monolayer vertical PN heterojunctions with planar-contacted electrodes (1Ls-VPNJ-PE) exhibit current rectification, but it originates from bending in the nonoverlapped region along the lateral direction. While 1Ls-VPNJs with vertically stacked graphene electrodes (1Ls-VPNJ-VE) have been demonstrated, the high tunneling current across the large overlapping junction area overshadows the relatively small rectification current of the PN diode. Here, we demonstrate current rectification in a sub-2 nm channel-length 1Ls-VPNJ-VE structure that consists of a vertically stacked carbon nanotube (CNT)/monolayer V-doped WS2 (p-type)/monolayer MoS2 (n-type)/CNT (C/V.W/M/C). Our C/V.W/M/C structure features an ultranarrow contact area, which suppresses the tunneling current to below 10 pA, thereby allowing the rectification current to dominate the total current flow. We propose a model for 1Ls-VPNJ-VE, in which the van der Waals (vdW) gap between the p-type and n-type monolayers prevents electrostatic coupling, enabling independent potential modulation in each monolayer. As a result, the built-in potential changes dynamically under forward and reverse biases, leading to clear rectification behavior. Additionally, the 1Ls-VPNJ-VE exhibits negative photoconductivity, attributed to an increased Schottky barrier at the CNTB/V.WS2 interface due to the trapping of photogenerated electrons in V-induced trap states. Benefiting from fast charge transfer in vertical vdW heterostructures, our 1Ls-VPNJ-VE demonstrates fast photoresponse with fall and rise times of 0.9 μs and 1.1 μs, respectively, approximately 100 times faster than the previous 1Ls-VPNJ-PE.