Mobility Limitations in TMD Monolayers: The Influence of Impurities and Remote Phonons

Two-dimensional (2D) monolayer transition metal dichalcogenides (TMDs) as a channel in field effect transistors (FETs) have been studied extensively due to their promise for high carrier mobility, better gate control, and decreased short channel effects. However, these promises were made by considering free-standing layers whereas in reality, the layers need to be surrounded by dielectrics. In our study, we avoid such ideality by considering a double gate geometry in which the TMD channel has a top (hBN/HfO
2
) and bottom (SiO
2
) dielectric. Although we might expect an enhancement of the impurity-limited mobility due to screening from high-κ dielectrics, this benefit is actually lost when we account for scattering with the hybrid interface plasmon/phonon excitations (IPPs) which is particularly strong in the presence of high-κ dielectrics. The aim of our study is to identify how ‘pure’ the TMD channel must be for IPP-scattering to take control of mobility. We use the well-established ab initio methods to calculate the band structure and bulk scattering rates and the full-band Monte Carlo method to calculate the mobility. Our results show that assuming the low-κ hBN as top-gate dielectric the crossover between IPPs and impurity scattering occurs for an impurity concentration around mid-10
¹¹
cm
⁻²
, whereas in structures with the high-κ HfO
2
top dielectric IPPs control the mobility at all impurity concentrations. Additionally, the carrier mobility exhibits a weak dependence on temperature with impurity scattering dominating at low temperatures.