TY - JOUR TI - Electronic properties and phase engineering of two dimensional MoS2 DO - https://doi.org/doi:10.7282/T39025HF PY - 2015 AB - There has been an increased interest in the research of 2D layered materials since the past few years especially after the discovery and physics related study of Graphene, a monolayer of graphite. Layered materials beyond graphene are the family of transition metal dichalcogenides (TMDs) which consist of over 40 members ranging from semiconductors to insulators to metals. All these materials are shown to be easily exfoliated to form monolayers which exhibit a new set of properties owing to the quantum confinement effects that occur during their exfoliation. The intrinsic thickness of less than 1nm per layer, lack of dangling bonds, controllable bandgap and precise control of thickness has aroused the interest of electrical engineers all over the world to use these materials for future electronics and make the dream of all 2D electronics to become true. Field effect transistors made from TMD semiconductors (MoS2, WS2, MoSe2, WSe2 etc.) are exhibiting excellent characteristics namely ON/OFF ratios in the range of 108, saturation currents exceeding 200 μA/μm, mobilities exceeding 100 cm2/Vs and subthreshold swings almost approaching the theoretical limit of 60 mV/dec. Though these values are impressive, they are far below their theoretical expectations, mainly due to the high contact resistance between the metal and semiconductor because of which their excellent intrinsic characteristics are not practically realized. There have been many efforts in mitigating this high contact resistance such as use of different contact metals, chemical doping of contact regions and long thermal annealing of devices which resulted in partial success. The aim of this work would be in establishing a universal strategy in reducing this high contact resistance to provide an ohmic-like contact between the metal and the TMD semiconductor by employing their phase-engineered metallic counterparts as the contacts. By fabricating transistors in which the electrode material and the channel similar is of the same material composition, many factors, which are detrimental to the operation of high performance transistors, can be eliminated. We have gained expertise in phase transformation of these transition metal dichalcogenides and successful utilized them as the contacts by locally patterning different phases on a single monolayer flake. We obtained record saturation currents, transconductances, mobilities and sub-threshold slopes for our novel transistors. This thesis will include details of synthesis of these TMD semiconductors, phase transformation and fabrication of transistors with lowered contact resistance with main emphasis on Molybdenum disulfide (MoS2). KW - Electrical and Computer Engineering KW - Semiconductors KW - Molybdenum disulfide KW - Transistors LA - eng ER -