Spatiotemporal carrier dynamics in graphene

Abstract: Graphene as an atomically thin material exhibits remarkable optical and electronic properties that suggest its technological application in novel optoelectronic devices, such as graphene-based photodetectors and lasers. To understand the properties of such devices on a microscopic level, we study the interplay of optical excitation, carrier-carrier, carrier-phonon, and carrierphoton scattering as well as diffusion processes. We apply a microscopic model based on the density matrix formalism with spatiotemporal graphene Bloch equations in its core. This approach provides microscopic access to the temporally, spectrally and spatially resolved carrier dynamics both in the presence and absence of an electric field, allowing the study of manyparticle mechanisms behind photodetection and gain in graphene. The focus of this thesis lies in modelling optics, dynamics and transport phenomena on consistent microscopic footing. We predict the possibility to achieve a stable population inversion in graphene, which is the crucial prerequisite for using graphene as an active material in a nanolaser. Further, we provide microscopic insights into the impact of an electric field on the carrier dynamics revealing the appearance of an efficient dark carrier multiplication that can even enhance the field-induced current. We also provide a microscopic foundation for the photoconduction and the bolometric effect as important mechanisms in a graphene based photodetector. Furthermore, we provide insights into the spatiotemporal dynamics of optically excited carriers, which create density and temperature gradients resulting in a diffusion of carriers. The gained insights can be used to study the thermoelectric effect and dynamics at interfaces of spatial inhomogeneities.