Book Description

The continuous miniaturization of electronic devices has given rise to structures whose dimensions do not exceed a few nanometers. At this size, electron transport can no longer be explained by simple drift and diffusion processes; electrons do not behave as point particles anymore but as propagating quantum-mechanical waves. In this thesis, we employ state-of-the-art quantum mechanical methods such as the non-equilibrium Green's functions and the density matrix method to study electron motion and light-matter interaction in nanostructures. We Will introduce new device functionalities that arise by tailoring two-dimensional materials such as graphene, phosphorene and transition-metal dichalcogenides (TMDs) into lower-dimensional nanostructures. In the first chapter we study electromagnetic field tuning of electronic properties of phosphorene and its nanoribbons. We show that by applying an electric field, phosphorene transitions from an insulator to a semimetal where a new type of quantum hall effect is observed. Later on, we show that near-equilibrium electron transport in metallic phosphorene nanoribbons takes place in the states whose wavefunctions are located near the edges of the ribbon. Electrical manipulation of these edge states provides a platform for the implementation of two different schemes of pseudospin electronics, a form of electronics based upon manipulation of tunable equivalents of the spin-one-half degree of freedom, i.e., the pseudospin. In chapter 2, we will introduce a numerically efficient density-matrix model applicable to midinfrared quantum cascade lasers. This model allows for inclusion of the lasing field and unlike previous models does not rely on phenomenologically introduced parameters. With the inclusion of lasing field a significant increase in the current density is observed, which leads to a better above-threshold agreement between the computed and experimental current density. In chapter 3, we study plasmon-enhanced optical non-linearity in low-dimensional nanostructures. We show that graphene nanomeshes and nanotriangles made of transition-metal dichalcogenides have great potential for applications in nonlinear nanophotonics. In particular, these nanostructures host plasmonic modes which can be easily excited and tuned for strong second- and third-harmonic generation.