Multiscale Modeling of Quantum Transport in 2D Material Based MoS Transistors

Abstract

Atomically thin 2D materials have ushered in a new era in the fi eld of nano-science and tech- nology and have been translated to notable advancements in the design of sensors, optoelectronic devices, exible electronics. These atomically thin materials are predicted to replace conven- tional bulk materials, Si and Ge, for transistor channels and extend the complementary metal oxide semiconductor technology road-map beyond the deca-nanometer regime. Constant efforts are being made to fabricate devices based on some of the recently discovered van der Waal's materials such as graphene, hexagonal boron nitride, MoS2, phosphorene. Apart from these, a large number of novel 2D materials and their derivatives are being constantly explored through both experiments and density functional theory analysis. In order to narrow down the mate- rial and design selection space for time- and cost-heavy experimental device fabrication, atomic level density functional theory (DFT) calculations need to be coupled with device-level physics models. Thus, we propose a multiscale computational framework bridging first principles based DFT calculations with device physics simulations. Under this framework, we start with crys- tallographic information of a 2D material and perform DFT simulations to extract important electronic parameters, such as effective mass, band gap, real and complex band dispersion, and phonon spectrum. This is followed by construction of the material hamiltonian based on the DFT extracted parameters. Next, the hamiltonian is used to perform self-consistent solution of the Schrodinger and the Poisson's equations through the non-equilibrium Green's function approach in order to describe the complex, spatially heterogeneous intrinsic carrier transport and resulting device performance in both ballistic and dissipative regimes. Modeling studies on three devices: (i) monolayer germanane metal oxide semiconductor fi eld effect transistors (MOSFETs), (ii) monolayer GeSe based tunneling field effect transistor (TFET), and (iii) phosphorene based MOSFET and TFET, will be presented in the thesis and their design and performance limits will be evaluated to guide future material selection and device fabrication.