Remote free-carrier screening to boost the mobility of Fröhlich-limited 2D semiconductors

Abstract

Van der Waals heterostructures provide a versatile tool to not only protect or control, but also enhance the properties of a 2D material. We use ab initio calculations and semi-analytical models to find strategies which boost the mobility of a current-carrying 2D semiconductor within an heterostructure. Free-carrier screening from a metallic "screener" layer remotely suppresses electron-phonon interactions in the current-carrying layer. This concept is most effective in 2D semiconductors whose scattering is dominated by screenable electron-phonon interactions, and in particular the Fröhlich coupling to polar-optical phonons. Such materials are common and characterised by overall low mobilities in the small doping limit, and much higher ones when the 2D material is doped enough for electron-phonon interactions to be screened by its own free carriers. We use GaSe as a prototype and place it in a heterostructure with doped graphene as the "screener" layer and BN as a separator. We develop an approach to determine the electrostatic response of any heterostructure by combining the responses of the individual layers computed within density-functional perturbation theory. Remote screening from graphene can suppress the long-wavelength Fröhlich interaction, leading to a consistently high mobility around $500$ to $600$ cm${}^2$/Vs for carrier densities in GaSe from $10^{11}$ to $10^{13}$ cm${}^{-2}$. Notably, the low-doping mobility is enhanced by a factor 2.5. This remote free-carrier screening is more efficient than more conventional manipulation of the dielectric environment, and it is most effective when the separator (BN) is thin.

20 pages, 14 figures

References in corpus (8)

• Quantum ESPRESSO: a modular and open-source software project for quantum simulations of materials
• Advanced capabilities for materials modelling with Quantum ESPRESSO
• 2D materials and van der Waals heterostructures
• Boron nitride substrates for high-quality graphene electronics
• Van der Waals heterostructures for high-performance device applications: challenges and opportunities
• Linear density response function in the projector-augmented wave method: Applications to solids, surfaces, and interfaces
• Valley-engineering mobilities in two-dimensional materials
• Density-functional calculation of static screening in 2D materials: the long-wavelength dielectric function of graphene