Electronic Structure and Transmission of Zigzag Graphene Nanoribbons under External Perturbation: Grand-Canonical Approach on Quantum Transport

Abstract

Zigzag graphene nanoribbon (zGNR) of narrow width has a moderate energy gap in its antiferromagnetic ground state. So far, first-principles electron transport calculations have been performed using density functional theory (DFT) combined with nonequilibrium Green function (NEGF) theory, while the transport calculation with the bottom-gate control has not been studied because it requires electron reservoir which allows chemical equilibrium between electrons in zGNR and electrodes. In this thesis, I present the iso-chemical potential scheme in grand canonical ensemble approach to describe the top/back-gate effect using external potential. Then, we examine the change in electronic state under the modulation of chemical potential and the subsequent electron transport phenomena in zGNR transistor under substantial top/back-gate and bias voltages. The new additional electronic states arising from gate potential bring about a boosted current. This gate-controlled current-boosting could be utilized for designing novel zGNR field effect transistors (FETs). Motivated by the phase transition behavior of zGNR, I present the band structure analysis of zGNR with respect to the external transverse electric field. Origin of weak ferromagnetism under high electric field was revealed as local repulsion term of Hamiltonian. Functionalization of edges to introduce innate electric field effect can also affect the stability of strong ferromagnetic state.