Monolayer MoS2-based heterostructure devices on Silicon and Flexible Substrates /

Includes bibliographical references.

PhD ; 2024 ; Instrumentation and Applied Physics

This work presents a comprehensive study of MoS2-based field-effect transistors (FETs), investigating three key aspects: hysteresis effects, asymmetric I-V characteristics, and piezoelectric properties. Through an exploration of these phenomena, this research provides valuable insights into the functional versatility of MoS2 FETs, with implications for memory devices, flexible electronics, and strain-engineered applications. The study begins by examining the hysteresis behaviour in surface-engineered MoS2 FETs, identifying how trap states influence device response under varied sweep rates, gate biases, voltage ranges, and temperatures. Enhanced hysteresis in plasma-treated devices is linked to gate oxide and MoS2-SiO2 interface traps, demonstrating a tuneable memory effect in MoS2 FETs via surface treatment. In exploring asymmetric I-V characteristics, the research uncovers a reproducible asymmetry in monolayer and multilayer MoS2 devices, unaffected by source-drain orientation. The results reveal that gate proximity, hBN dielectric layers, and interfacial effects contribute to this behaviour, suggesting that factors beyond Schottky barriers contribute to the phenomena. The study finds that, under certain strain conditions, the asymmetry can even flip in flexible graphite-gated devices. This highlights the influence of gate materials and configurations on the transport properties of 2D materials and sets the stage for deeper investigation. To address fabrication challenges on flexible substrates, optimized processes were developed for MoS2 heterostructures and graphite gated devices were fabricated. Enhancement in strain response is reported for gated 1L-MoS2 devices, enabling precise strain-sensitive measurements. Building on this, the study evaluates the piezoelectric and transport responses of these flexible devices under cyclic bending, achieving consistent, controllable strain responses, including strain-induced switching. These advancements confirm the potential of MoS2-based FETs in real-time strain-sensing applications, establishing a foundation for flexible electronics with significant potential in fields like valleytronics, piezotronics, and optoelectronics.