  Two-dimensional (2D) layered transition metal dichalcogenides (TMDCs) are
promising memristive materials for neuromorphic computing systems as they could
solve the problem of the excessively high energy consumption of conventional
von Neumann computer architectures. Despite extensive experimental work, the
underlying switching mechanisms are still not understood, impeding progress in
material and device functionality. This study reveals the dominant role of
mobile defects in the switching dynamics of 2D TMDC materials. The switching
process is governed by the formation and annihilation dynamics of a local
vacancy depletion zone. Moreover, minor changes in the interface potential
barriers cause fundamentally different device behavior previously thought to
originate from multiple mechanisms. The key mechanisms are identified with a
charge transport model for electrons, holes, and ionic point defects, including
image-charge-induced Schottky barrier lowering (SBL). The model is validated by
comparing simulations to measurements for various 2D MoS$_2$-based devices,
strongly corroborating the relevance of vacancies in TMDC devices and offering
a new perspective on the switching mechanisms. The insights gained from this
study can be used to extend the functional behavior of 2D TMDC memristive
devices in future neuromorphic computing applications.
