Abstract

This thesis is an attempt to understand and delve into the realm of atomistic simulations, using it to understand a novel set of materials called Transition Metal Dichalcogenides (TMDs). We use NEMO5 and MedeA-VASP to calibrate and characterize a few selected TMDs and to validate our understanding of atomistic modeling we simulated a tunnel field-effect transistor with monolayer TMD as a channel using NEMO5. TFETs offer great advantages over MOSFET (metal oxide field-effect devices) like, sub-60 mV/dec sub-threshold swing, minimal leakage current, high switching speed, and small power requirements. Low drive current has prevented TFETs from becoming a mainstream device instead of MOSFETs. Two methods of improving TFETs are being considered: one, making the device out of single-layered materials, and two, using different kinds of materials, TMDs being one of them. This research uses NEMO5 and MedeA-VASP atomistic modeling tools to understand both of the device improvement approaches mentioned above. Variation in parameters that matter at the atomic scale, like high symmetry k-point path, k-point meshing, and plane-wave cut-off energy exhibit prominent effects on the band-structure of a material. NEMO5 E-k band structures were simulated for TMDs like MoS2 and WTe2 and the band-gap structures obtained were compared with literature. Structure denition and atomistic device simulation were conducted in NEMO5. A TFET with a monolayer of MoS2 as a channel was simulated to see the I-V characteristics obtained from the NEMO5 tool. By performing electronic band-structure simulations with and without spin-orbit coupling (SOC) and comparing it against electronic structures presented in literature, it is shown that consideration of SOC is necessary for accurate results. Atomistic simulations are computationally intensive and this work also explored the effects of parametric and distributed computing settings on simulation times.

Publication Date

Spring 2019

Document Type

Thesis

Student Type

Graduate

Degree Name

Microelectronic Engineering (MS)

Department, Program, or Center

Microelectronic Engineering (KGCOE)

Advisor

Sean Rommel

Advisor/Committee Member

Karl Hirchman

Advisor/Committee Member

Santosh Kurinec

Campus

RIT – Main Campus

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