Mobility enhancement and temperature dependence in top-gated single-layer MoS2

TL;DR

This study quantitatively explains how high-$$ oxide overlayers enhance electron mobility in single-layer MoS$_2$ at room temperature, emphasizing the roles of temperature-dependent screening and impurity scattering.

Contribution

The paper provides a detailed model of impurity-limited mobility in single-layer MoS$_2$, accounting for temperature effects and oxide thickness, which advances understanding of mobility enhancement mechanisms.

Findings

Mobility enhancement is greater at low electron densities and high temperatures.

Mobility decreases significantly with increasing temperature, influenced by impurity scattering.

Reducing HfO$_2$ thickness from 20 nm to 2 nm can improve mobility by about 37%.

Abstract

The deposition of a high-$\kappa$ oxide overlayer is known to significantly enhance the room-temperature electron mobility in single-layer MoS$_{2}$ (SLM) but not in single-layer graphene (SLG). We give a quantitative account of how this mobility enhancement is due to the non-degeneracy of the two-dimensional electron gas system in SLM at accessible temperatures. Using our charged impurity scattering model [Ong and Fischetti, Phys. Rev. B 86, 121409 (2012)] and temperature-dependent polarizability, we calculate the charged impurity-limited mobility ($\mu_{\textrm{imp}}$) in SLM with and without a high-$\kappa$ (HfO$_{2}$) top gate oxide at different electron densities and temperatures. We find that the mobility enhancement is larger at low electron densities and high temperatures because of finite-temperature screening, thus explaining the enhancement of the mobility observed at room temperature. $\mu_{\textrm{imp}}$ is shown to decrease significantly with increasing temperature, suggesting that the strong temperature dependence of measured mobilities should not be interpreted as being solely due to inelastic scattering with phonons. We also reproduce the recently seen experimental trend in which the temperature scaling exponent ($\gamma$) of $\mu_{\textrm{imp}}\propto T^{-\gamma}$ is smaller in top-gated SLM than in bare SLM. Finally, we show that a $\sim37$ percent mobility enhancement can be achieved by reducing the HfO$_{2}$ thickness from 20 to 2 nm.