Investigation of Graphene-MoS2 Heterostructures in a Multiple Field-Effect Transistor Architecture

Van der Waals (vdW) heterojunctions between graphene and transition metal dichalcogenides (TMDs) are a key building block of electronic and optoelectronic devices based on two-dimensional crystals. Their stacking sequence is generally believed to affect their behavior as contacts in field-effect transistor (FET). In this Ph.D. thesis, a novel multiple FET architecture is presented, consisting of a MoS2 FET with graphene contacts, where each graphene contact can act itself as a FET. This novel architecture allowed the experimental and theoretical investigation of how a TMD can screen graphene even when it would not be expected to. In the current study, both monolayer MoS2 and graphene were synthesized by chemical vapor deposition (CVD) in a monocrystalline form. Charge transport measurements were performed at room temperature in both configurations. At room temperature, MoS2 FETs show highly linear IV characteristics and a mobility up to 8.6 cm2/Vs, while graphene stripes display quenched n-type conduction depending on the MoS2 overlay coverage percentage. Low-temperature measurements have allowed the evaluation of the Schottky barrier height between MoS2 and graphene. Materials properties are tracked at each step of fabrication by photoluminescence (PL), and Raman spectroscopies. The latter reveals a charge transfer within the heterojunctions.