Origin of contact polarity at metal-2D transition metal dichalcogenide interfaces

Abstract

Using state-of-the-art ab initio GW many-body perturbation theory calculations, we show that monolayer MoS2 on Au is a p-type contact, in contrast to the vast majority of theoretical predictions using density functional theory. The predominantly n-type behaviour observed experimentally for MoS2/Au junctions can be attributed to the presence of sulfur vacancies, which pin the Fermi level. GW calculations on WSe2/Au junctions likewise predict p-type contacts for pristine WSe2 and n-type contacts for junctions with selenium vacancies. Experimentally, WSe2/metal junctions are predominantly p-type or ambipolar, with p-type junctions being observed for selenium-deficient WSe2, suggesting that selenium vacancies are not effective in pinning the Fermi level for WSe2/metal junctions. We rationalize these apparently contradictory results by noting that selenium vacancies in WSe2 are readily passivated by oxygen atoms. Taken together, our state-of-the-art calculations clearly elucidate the relation between contact polarity and atomic structure. We show that non-local exchange and correlation effects are critical for determining the energy level alignment and even the contact polarity (in the case of MoS2 on Au). We further reconcile a large body of experimental literature on TMDC/metal contact polarities by consideration of the defect chemistry.

A Predictive Model for Monolayer‐Selective Metal‐Mediated MoS2 Exfoliation Incorporating Electrostatics

“…This causes electron depletion in the semiconducting MoS 2 layer (see further discussion in Section S3, Supporting Information). [ 43,44 ] Indeed, the 1L‐MoS 2 /metal interfaces reduced the electron density ( Δn e < 0) of the 1L‐MoS 2 (Figure 1I), suggesting formation of Schottky junctions. [ 39 ] A correlation is observed between the ideal built‐in potential (Φ i ) and Δn e , where Φ i is calculated as follows: $$$$\begin{equation}{\Phi }_i = {\Phi }_M - {X}_{Mo{S}_2} - \left( {{E}_F - {E}_C} \right)\end{equation}$$$$where $${X}_{Mo{S}_2}$$ is the 1L‐MoS 2 electron affinity, and E F and E C are the Fermi level and conduction band minimum, respectively.…”

“…This causes electron depletion in the semiconducting MoS 2 layer (see further discussion in Section S3, Supporting Information). [43,44] Indeed, the 1L-MoS 2 /metal interfaces reduced the electron density (Δn e < 0) of the 1L-MoS 2 (Figure 1I), suggesting formation of Schottky junctions. [39] A correlation is observed between the ideal built-in potential (Φ i ) and Δn e , where Φ i is calculated as follows:…”

Antimony–Platinum Modulated Contact Enabling Majority Carrier Polarity Selection on a Monolayer Tungsten Diselenide Channel

“…We infer that high workfunction metals like Pd and Pt do induce some degree of perturbation in the WSe 2 lattice. 29,30 This disturbance can be manifested as the introduction of defects 31,32 or as interfacial chemical bonding, thereby resulting in the defect-induced gap states (DIGS) or MIGS, i.e., FLP effect. In other words, the semimetallic Sb layer causes less disruption to the WSe 2 lattice.…”