SELECTED ISSUES FACING THE USE OF TWO-DIMENSIONAL MATERIALS IN TRANSISTORS

Abstract

Recently, 2D materials have received considerable attention, owing to their exceptional properties, for various applications from electronics to biochemical sensing. Despite the rapid development in 2D materials research, many challenges and opportunities remain unexplored for 2D electronic devices. This thesis addresses emergent issues that impede the use of graphene and molybdenum disulphide (MoS2) for transistor applications: (1) poor metal-graphene contacts, (2) Fermi level pinning in MoS2 devices, and (3) threshold voltage control in MoS2 transistors. To achieve low-resistance metal-graphene contacts, multiple nano-sized pits are created in graphene with zigzag-terminated edges that covalently bond to metal. Furthermore, we show that the metal-graphene system is a better electrode candidate for MoS2 devices compared to metal, because of its smaller work function. Finally, the underlying physics and capability to control the threshold voltage in MoS2 field-effect transistors are elucidated through a combination of experimental evidence and first-principles calculations.