Emission properties of high-β nanolasers with continuous gain media

The search for ever smaller and more efficient sources of coherent light motivated the development of lasers with dimensions on the nanoscale. These consist of dielectric or metallic cavity structures that confine light close or even below the diffraction limit and can be integrated into on-chip photonics which makes them interesting candidates for applications in quantum information and communication and integrated photonic circuits. While semiconductor quantum dots were much investigated as gain media for such lasers, recently also extended, two- dimensional gain media are considered. Semiconductor quantum wells are already employed in micro laser (e.g. VCSELs) on an industrial scale, and, improved fabrication techniques, have now been pushed to the nanoscale as well. Furthermore, new classes of atomically thin 2d layers of transition metal dichalcogenide (TMD) have emerged as an exciting candidate for optical applications due to their strong optical activity.
In this thesis we contribute to the field by developing and employing quantum-optical semiconductor laser models that give direct access to conventional laser characteristics as well as photon-correlation functions. Using equation of motion techniques and the cluster-expansion approximation we find that nanolasers with extended gain media operating close to the thresholdless regime have a distinctly different threshold behavior in comparison to quantum-dot-based nanolasers. These findings shed new light on the behavior of nanolaser in their transition from thermal to coherent emission. Furthermore we provide gain calculations for single layers of different TMD materials, that take into account many-body interaction leading to band structure renormalizations and dephasing processes. Together with a rate-equation theory that is adapted to account for the particular device geometry, we highlight prospects and limitations of TMD materials for applications in nanolasers. Finally we develop a quantum-optical semiconductor laser theory that we apply to the description of realistic quantum-well-based nanolasers. Together with experimental partners we unambiguously show the onset of lasing emission from different device types and create a comprehensive picture of the internal processes that define the dynamics of these devices.