Canonical Schottky barrier heights of the transition metal dichalcogenide monolayers in contact with a metal

TL;DR

This paper investigates the Schottky barrier heights of transition metal dichalcogenide monolayers in contact with metals, using theoretical models to analyze their behavior and the influence of metal-induced gap states, including spin-orbit effects.

Contribution

It provides a theoretical analysis of Schottky barrier heights in $MX_{2}$ monolayers, emphasizing the role of metal-induced gap states and including spin-orbit coupling considerations.

Findings

Charge neutrality levels are near mid-gap, consistent with previous reports.

Calculated Schottky barrier heights agree with experimental and computational data for small electronegativity differences.

Spin-orbit effects do not alter the fundamental metal-induced gap state character of the barriers.

Abstract

The transition metal dichalcogenide ($MX_{2}$, where $M$=Mo, W and $X$=S, Se, Te) monolayers are of high interest for semiconducting applications at the nanoscale level; this interest is due to both their direct band gaps and high charge mobilities. In this regard, an in-depth understating of the related Schottky barrier heights, associated with the incorporation of $MX_{2}$ sheets into novel low-dimensional metal-semiconductor junctions, is of crucial importance. Herein, we generate and provide analysis of the Schottky barrier heights behavior to account for the metal-induced gap states concept as its explanation. In particular, the present investigations concentrate on the estimation of the charge neutrality levels directly by employing the primary theoretical model, $i.e.$ the cell-averaged Green's function formalism combined the complex band structure technique. The results presented herein place charge neutrality levels in the vicinity of the mid-gap; this is in agreement with previous reports and analogous to the behavior of three-dimensional semiconductors. The calculated canonical Schottky barrier heights are also found to be in agreement with other computational and experimental values in cases where the difference between electronegativities of the semiconductor and metal contact is small. Moreover, the influence of the spin-orbit effects is herein considered and supports that Schottky barrier heights have metal-induced gap state-derived character, regardless whether spin-orbit coupling interactions are considered. The results presented within this report constitute a direct and vital verification of the importance of metal-induced gap states in explaining the behavior of observed Schottky barrier heights at $MX_{2}$-metal junctions.