Optoelectronic Properties of Two-Dimensional Materials
MetadataShow full item record
Layered materials when thinned down to their monolayer limit exhibit remarkable properties owing to their two-dimensional nature and strong electron confinement. In particular this class of materials displays strong optical properties, showing promise for applications towards future optoelectronic devices; however, due to their relative recent isolation, the optical properties of these monolayers have been largely unexplored. This thesis focuses on the interaction of these layered materials with incident optical radiation, with the focus being on monolayers of WSe$_2$ and graphene. In the first half of this thesis the strong excitonic physics of semiconducting WSe$_2$ monolayers is investigated. These excitons exhibit large interaction effects due to the strong 2D confinement which are further explored here using ultrafast pump probe techniques. Additionally these excitons possess a unique quantum degree of freedom, known as the valley pseudospin. It has been shown that this pseudospin can be optically addressed and readout using its unique circular dichroism. Here the degenerate pseudospin is controlled using an external magnetic field coupled to its valley pseudospin magnetic moment. From this work the valley pseudospin in monolayer WSe$_2$ can be further explored as a possible qubit in future quantum computing and quantum information applications. Graphene photodetectors are the focus of the second half of the thesis. Monolayer graphene is a gapless semi-metal that has been shown to display an ultrafast optoelectronic response that is dominated by hot carriers. Here these effects are investigated as a band gap is generated through the application of a perpendicular electric field in bilayer graphene and through the application of a perpendicular magnetic field in monolayer graphene inducing a Landau level quantization of the band structure. It is observed that in both cases the disruption of the continuous band structure has profound impacts on the photo-excited hot carriers. This work helps lay the foundation for future ultrafast photodetectors made out of graphene.
- Physics