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

To achieve better properties of van der Waals (vdW) devices, vdW heterointerfaces with substrates such as hexagonal boron nitride (h-BN) were introduced to alleviate adverse substrate effects. However, the premature dielectric breakdown and its scale limitation make wider application of h-BN substrates challenging. Here we report a fluoride-based substrate that substantially improves optoelectronic and transport properties of dichalcogenide devices, with enhancement factors comparable to 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 show that the constructed SnS₂/CaF₂ and WS₂/CaF₂ devices exhibit 1 order of magnitude higher than devices based on the SiO₂ substrate in electronic mobility and photoresponsivity. Theoretical calculations reveal that devices based on fluoride substrates are immune from the Coulomb impurity scattering by forming quasi-vdW interfaces, exhibiting great potential for high responsivity and mobility of photogenerated carriers in 2D vdW devices.