Modular van der Waals MOSFETs through layer-by-layer chalcogen substitutions.

In two-dimensional transition-metal dichalcogenides (TMDCs), the local electrostatic field of the chalcogen p-orbitals dictates the crystal field splitting of the transition metal d-orbitals, stabilizing diverse electronic states from semiconducting and semimetallic to exotic topological phases. On-demand substitution of the lattice chalcogens is therefore an efficient route to tuning TMDC electronic phases. Here, we custom-molded van der Waals (vdW) heterostructures by layer-by-layer vapor-phase chalcogen substitution starting from p-type WSe2 multilayers into which we locally inscribed insulating WOx, n-type WS2, and semimetallic WTe2. This spatially precise conversion seamlessly integrated distinct electronic phases, both vertically and laterally, into modular vdW semiconductor heterostructures that are otherwise inaccessible. As a demonstration, we integrated WOx/WSe2 local gate stacks to build ultrascaled metal oxide-semiconductor field effect transistors (MOSFETs), achieving an unprecedented subthreshold swing at subnanometer equivalent oxide thickness.