Enhanced Transport and Optoelectronic Properties of van der Waals Materials on CaF₂ Films

To achieve better properties of van der Waals (vdW) devices,vdWheterointerfaces with substrates such as hexagonal boron nitride (h-BN)were introduced to alleviate adverse substrate effects. However, thepremature dielectric breakdown and its scale limitation make widerapplication of h-BN substrates challenging. Here we report a fluoride-basedsubstrate that substantially improves optoelectronic and transportproperties of dichalcogenide devices, with enhancement factors comparableto those of h-BN. A model system of wafer-scale fluoride calcium (CaF2) ultrathin films with the preferable growth direction along[111] is prepared by the magnetron sputtering method. Results showthat the constructed SnS2/CaF2 and WS2/CaF2 devices exhibit 1 order of magnitude higher thandevices based on the SiO2 substrate in electronic mobilityand photoresponsivity. Theoretical calculations reveal that devicesbased on fluoride substrates are immune from the Coulomb impurityscattering by forming quasi-vdW interfaces, exhibiting great potentialfor high responsivity and mobility of photogenerated carriers in 2DvdW devices.