Barrier Formation at the Contacts of Vanadium Dioxide and Transition-Metal Dichalcogenides.

Phase-transition field-effect transistors (FETs) are a class of steep-slope devices that show abrupt on/off switching owing to the metal-insulator transition (MIT) induced in the contacting materials. An important avenue to develop phase-transition FETs is to understand the charge injection mechanism at the junction of the contacting MIT materials and semiconductor channels. Here, toward the realization of high-performance phase-transition FETs, we investigate the contact properties of heterojunctions between semiconducting transition-metal dichalcogenides (TMDCs) and vanadium dioxide (VO) that undergoes a MIT at a critical temperature () of approximately 340 K. We fabricated transistors based on molybdenum disulfide (MoS) and tungsten diselenide (WSe) in contact with the VO source/drain electrodes. The VO-contacted MoS transistor exhibited n-type transport both below and above . Across the MIT, the on-current was observed to increase only by a factor of 5, in contrast to the order-of-magnitude change in the resistance of the VO electrodes, suggesting the existence of high contact resistance. The Arrhenius analyses of the gate-dependent drain current confirmed the formation of the interfacial barrier at the VO/MoS contacts, irrespective of the phase state of VO. The VO-contacted WSe transistor showed ambipolar transport, indicating that the Fermi level lies near the mid gap of WSe. These observations provide insights into the contact properties of phase-transition FETs based on VO and TMDCs and suggest the need for contact engineering for high-performance operations.