Modulating Electronic Transport in MoS2 Field-effect Transistor: Voltage-programmable Bimodal Switching and Substitutional Doping

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising platforms for next-generation nanoelectronics owing to their atomically thin body, tunable electronic structures, and defect-tolerant surfaces. In particular, the ability to dynamically modulate charge transport properties through external stimuli—such as electrostatic gating, chemical doping, and phase engineering—has opened new frontiers for functional device architectures. However, a major challenge remains in simultaneously achieving precise, stable, and reversible control of charge transport across broad operating regimes. Addressing this challenge is critical for the realization of reconfigurable and multifunctional 2D devices. In this thesis, we investigated two complementary strategies for charge transport modulation in MoS2 transistors: (i) field-programmable bimodal switching through hybrid dual gating, and (ii) substitutional doping for controlled carrier concentration engineering. To enable dynamic and programmable switching, we first introduce a hybrid-dual-gated (HyDG) MoS2 transistor that integrates a high-k solid dielectric and an ionic liquid electrolyte as dual gating layers. This architecture allows the selective activation of two distinct switching modes—near- Boltzmann-limit electrostatic switching and intercalation-driven metal-insulator transitions—within a single device flatform. By synchronously modulating dual-gate voltages, the device achieves both steep-slope electrostatic switching at low biases and reversible phase transitions at higher biases, offering a versatile platform for multimodal operation (Chapter 2). In parallel, we develop an in-situ carrier modulation strategy via MOCVD-enabled substitutional vanadium (V) doping in MoS2, enabling precise dopant control across a wide doping spectrum. Beyond conventional doping approaches, the achieved heavily-doped metallic films serve as buffer layers at the 2D semiconductor–metal electrode interface, effectively mitigating metal-induced gap states (MIGS) and suppressing Fermi level pinning. This engineered interface significantly enhances carrier injection efficiency into p-type MoS2 channels. Our approach highlights a scalable and tunable technique for charge and phase modulation, which is indispensable for the realization of high-performance 2D material-based electronic devices (Chapter 3). Together, these two charge transport modulation strategies offer a versatile tool for dynamically controlling electronic phases, carrier concentrations, and interfacial properties in 2D semiconductor systems. By enabling precise, reversible, and scalable tuning of material properties, they lay the technological strategies for future applications in reconfigurable logic circuits, low-power electronics, and advanced vdW heterostructure devices. The integration of multimodal switching and contact interface engineering represents a critical step toward the realization of high-performance and multifunctional 2D nanoelectronics.