Charge Transport Calculation along Two‐Dimensional Metal/Semiconductor/Metal Systems

Abstract

Two-dimensional transistors are promising candidates for the next generation of nanoscale devices. Like the other alternatives, they also encounter problems such as instability under standard condition (STP), low channel mobility, small band gaps, and difficulty to integrate metal contacts. The latter poses a great challenge since metal/ semiconductor interface significantly affects the transistor's performance. Some of these obstacles can be solved by using two-dimensional transition metal di-chalcogenides (TMDC) materials. In this study, we performed charge transport calculation based on density functional theory (DFT) followed by wave dynamics to evaluate the performance of six two-dimensional TMDC metal/semiconductor/ metal systems. Each semiconductor monolayer was laterally connected, at both ends to metal contacts consisting of VS 2 or FeS 2 monolayers. We found that charge transport was more efficient in systems containing a CrS 2 semiconductor monolayer compared to systems with MoS 2 or WS 2 as the semiconductor monolayer. The electronic characterization of the monolayer TMDC materials by DFT estimates well the trend in charge transport efficiency calculated using wave packet dynamics.

The Role of Electron–Electron Interaction in Charge Transport Calculations through Transition Metal Dichalcogenides Heterojunctions

“…σ is the standard deviation of position for both electrons, converged to 1 Å w.r.t the total energy as shown in previous 1D calculations. [ 15,16 ]…”

“…These layer lengths were found to be long enough to reproduce the bulk monolayer properties in the unit cell located at midlayer, far from the interfaces for both metal and SC. [ 15 ] The lattice constant of the heterojunction's supercell was taken to be the average lattice constants of the metal and SC monolayers that compose it. For the dynamic calculation, both electrons were initially located on the metal monolayer.…”

“…Based on the definition of the expectation value for kinetic energy and the relation described in Equations (7) for the wave function in Equation (1), the initial wave numbers, and , can be calculated according to Equation (8). [ 15 ] where L is the length of the heterojunction, is the initial electron location, A is the normalization constant of the wave function, ℏ is the reduced Planck constant, and σ is the standard deviation of position. This equation can be solved seeing that all variables of Equation (8) are known except .…”

“…Large‐scale calculations have been demonstrated by combining ab initio and numerical methods. [ 3–5 ] A widely used approach to calculate charge transport properties of nanoscale conductors is nonequilibrium Green's function theory, [ 7,11 ] although computationally costly, has been successfully used to describe electron–phonon coupling [ 12,15 ] and electron–electron interaction. [ 16,17 ]…”

“…Nevertheless, for all systems, the interaction increases charge transmission probability from the metal to the semiconductor, due to electronic repulsion that pushes one of the charge carriers forward across the interface. calculate charge transport properties of nanoscale conductors is nonequilibrium Green's function theory, [7,11] although computationally costly, has been successfully used to describe electronphonon coupling [12,15] and electron-electron interaction. [16,17] In this work, we use an efficient multiscale approach based on density functional theory (DFT) followed by wave propagation along a 1D chain of TMDC unit cells.…”