Effect of two-dimensional nonlocal screening on mobility of electrons in transition-metal dichalcogenide monolayers

TL;DR

The paper addresses mobility limitations in two-dimensional transition-metal dichalcogenide (TMD) monolayers arising from Coulomb impurity scattering and introduces a two-dimensional nonlocal screening framework to account for wave-vector dependent dielectric screening. It builds a theoretical model for the screened Coulomb interaction and transport relaxation time, incorporating macroscopic nonlocal screening and electronic screening through a polarization function, and computes mobility from a finite-temperature transport average. The key finding is that nonlocal screening enhances electron mobility by several times across a range of carrier densities and substrates, with the largest gains for low-dielectric environments such as SiO2 and for free-standing monolayers; at room temperature the enhancement can reach about 6–9× on SiO2. This work underscores the importance of nonlocal dielectric screening in accurate mobility modeling for TMD-based devices and provides guidance for substrate choice and device design, especially at elevated temperatures where conventional models underestimate mobility gains.

Abstract

A new mechanism for charge carrier scattering in transition-metal dichalcogenide monolayers is proposed on the basis of the theory of two-dimensional nonlocal screening developed for the dielectric function of thin-layer insulating materials (P. Cudazzo et al. PRB 84, 085406 (2011)). The expressions for the transport relaxation time and for the electron mobility are obtained for electrons scattering on Coulomb impurity centers in monolayers of transition-metal dichalcogenide on various substrates. It is found that taking nonlocal screening into account increases the mobility of electrons by several times. Although the value of the mobility decreases with increasing temperature, the relative enhancement due to nonlocal screening grows 6-9 times at room temperature, in the case of SiO$_2$ substrate.

Figures (7)

• Figure 1: The dependencies of the mobility in TMD monolayers on electron concentration for $T=0$K and for various substrates in the case of $\delta = 0$: a. for MoS$_2$ and MoSe$_2$, b. for WS$_2$ and WSe$_2$.
• Figure 2: The dependencies of the mobility ratios in TMD monolayers on electron concentration for $T=0$K and for various substrates.
• Figure 3: The dependencies of the mobility of TMD monolayers on electron concentration for different temperatures in case of $\delta=0$ ((a), (b), (c)). In (d) the electron mobility in MoS$_2$ TMD on different substrates is presented at $T=10$K.
• Figure 4: The dependencies of the mobility of TMDs monolayers on electron concentration for different temperatures in case of $\delta \neq 0$ ((a), (b), (c)). In (d) the electron mobility in MoS$_2$ TMD on different substrates is presented at $T=10$K.
• Figure 5: The dependencies of the mobility in MoS$_2$ monolayer on temperature for various substrates and concentrations of electrons and scattering centers in the case of $\delta = 0$.