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

Van der Waals heterostructures provide a versatile tool to manipulate the properties of 2D materials and optimize their performance. Here we use ab initio calculations and semi-analytical models to find strategies that boost the mobility of a current-carrying 2D semiconductor by including a metallic layer in the heterostructure. Free-carrier screening from the metallic "screener" remotely suppresses electron-phonon interactions in the current-carrying layer, thus enhancing mobility. This concept is most effective in 2D semiconductors whose scattering is dominated by electron-phonon interactions which are sensitive to screening, in particular the common case of Fröhlich coupling. To obtain the screened interaction we develop a novel approach to combine the electrostatic response of any heterostructure, based on the response of the individual layers computed within density-functional perturbation theory. We use GaSe as a prototype, and place it in an heterostructure with doped graphene as the "screener" layer and BN as a separator. Remote screening leads to an enhancement by a factor 3 in GaSe, with a mobility that is almost constant, around 500 to 600 cm²/Vs, over a wide range of carrier densities from from 10¹¹ to 10¹³ cm^-2.