Vertical Nonvolatile Schottky‐Barrier‐Field‐Effect Transistor with Self‐Gating Semimetal Contact

Abstract

Emerging 2D nonvolatile Schottky‐barrier‐field‐effect transistors (NSBFETs) are envisaged to build a promising reconfigurable in‐memory architecture to mimic the brain. Herein, a vertically stacked multilayered graphene (MGr)‐molybdenum disufide (MoS2)‐tungsten ditelluride (WTe2) NSBFET is reported. The semimetal WTe2 with the charge‐trapping effect enables the simultaneous integration of the electrode and the self‐gating function. The effective Schottky barrier height offset ΔΦB is programed from ΔΦB‐p = 132.6 meV to ΔΦB‐n = 109.4 meV, inducing the reversed built‐in electric field to make the NSBFET, so as to provide one with a multifunctional platform to integrate the nonvolatility and the reconfigurable self‐powered photo response. The reversible open‐circuit voltages of NSBFET synapse are programmed from −0.1 to 0.25 V and the self‐powered responsivity with reversed signs is tuned from 290 to −50 mA W−1, which enables the representation of a signed weight in a single device to enrich multiple optical sensing and computing capabilities.

Vertical 1T’‐WTe2/WS2 Schottky‐Barrier Phototransistor with Polarity‐Switching Behavior

“…As shown in Figure 6f, the reconfigurable device exhibits negative I sc at V g = 60 V while a positive I sc is obtained at V g = -60 V, enabling a wide range of applications in retinomorphic hardware device, in-memory optical sensing, broadband convolution processing, and optoelectronic logic devices with light-actuated sensing ability. [21,30,68,69] In order to verify the reproducibility of our designed structure, the other two devices with similar reversed rectification behavior and bidirectional photoresponse are shown in Figure S13 (Supporting Information). To verify that reconfiguration is independent of charge capture at the SiO 2 /2D materials interface, we fabricated WTe 2 /WS 2 and h-BN/WS 2 /WTe 2 with similar thickness and performed repeated tests after one week, demonstrating both reliability and controllability in Figure S14 (Supporting Information).…”

“…By contrast, WTe 2 channel shows high conductance and cannot be modulated by V g , which is consistent with the semi‐metallic characteristics of multilayered 1T’‐WTe 2 . [ 29,30 ] In addition, the Fermi level of WTe 2 is also confirmed to be pinned at the VBM at room temperature regardless of V g . [ 29 ] As shown in Figure S2 (Supporting Information), the I ds ‐V ds curves for individual WS 2 and WTe 2 show linear and symmetric relationship between I ds and V ds , revealing the Ohmic contact between WS 2 or WTe 2 and Cr/Au electrode.…”

“…A nearly ideal power exponent (α = 1) of 0.95 at V g = 60 V illustrates a relatively lower Auger recombination of photo‐generated carriers driven by the large built‐in electric field in the WTe 2 /WS 2 junction. [ 59 ] When V g = 60 V, R monotonously decreases from 1325 to 667 mA W −1 with the increment of P. The maximum R value of 1325 mA W −1 under 635 nm illumination is superior to many other WTe 2 ‐based Schottky diodes such as MoTe 2 /WTe 2 , [ 29 ] Gr/MoS 2 /WTe 2 [ 30 ] and WTe 2 /MoS 2 heterostructures. [ 32 ] While V g = ‐60 V, R also slightly decreases from 644 to 410 mA W −1 with the increment of P. As known, the photovoltaic R reaches its maximum at weak P because of the neglectable non‐radiative recombination originating from the small number of filled trap states.…”

“…Second, in the case of multilayered graphene/MoS 2 /T d ‐WTe 2 , the carrier concentration or polarity in the overlapped channel can be regulated via external bias and V g , allowing for the manipulation of reversed built‐in electric field and tunable Schottky barrier height (SBH) for application in nonvolatile memorizers. [ 30 ] At last, the contact resistance can be reduced to an ultralow value by designing the Fermi level difference between the semimetal and semiconductor to approach the Schottky‐Mott limit. It can result in ultra‐high mobility and high on‐current density in field‐effect transistors such as 1T’‐WTe 2 /monolayer MoS 2 .…”

2D Dual Gate Field‐Effect Transistor Enabled Versatile Functions

“…Moreover, the atomic-thin 2D channel rendered the strong interaction between the overlapped top and bottom gates, which enabled the top gate to work as a floating gate and integrated the memory function. [29][30][31] Especially, compared with other low-dimensional materials such as quantum dots, [32] nanowires [33,34] and the 2D materials [35,36] are expected to bring the opportunity to achieve the electric gate tunable and programmable photoresponse. In this work, we fabricated a MoS 2 asymmetric dual-gate FET (ADGFET), where In 2 Se 3 serves as the top gate and Si substrate serves as the common back gate.…”