Theoretical modelling of semiconductor nanolasers: On the influence of many-body effects on the optical properties of semiconductor nanostructures

The rapid rise in global data centre energy consumption poses a critical challenge in the age of digitalisation and artificial intelligence. A promising strategy for improving energy efficiency involves the use of on-chip integrated photonic components to enable high-speed and low-loss optical links and photonic computing platforms. Realising this vision requires integrable laser sources on the nanoscale. This dissertation develops a comprehensive theoretical framework for semiconductor nanolasers, with a particular emphasis on the influence of quantum many-body effects on the optical properties of low-dimensional gain media.

This work is structured to consist of three interdependent chapters.
The first chapter investigates a metallic-cavity nanolaser incorporating multiple quantum wells. A fully quantised electromagnetic field formalism is employed and Quantum Laser Equations are derived on the quadruplet-level. These equations enable access to key observables including the input-output characteristics, coherence time, and second-order correlation function at zero delay. Theoretical predictions are shown to be in substantial agreement with experimental data from a silver-coated MQW nanolaser device. A spectral lineshape anomaly is identified: A transition from a Lorentzian to a Gaussian emission profile at the lasing threshold, attributed to intrinsic non-linear effects and partial mode-locking in the open cavity system.
The second chapter establishes a microscopic model of monolayer molybdenum disulfide, a transition metal dichalcogenide, as a gain material. Based on a tight-binding approach, material-specific dipole and Coulomb matrix elements are derived and energy renormalisations via the screened-exchange Coulomb-hole approximation are introduced to account for the influence of screening due to the presence of excited carriers. Absorption spectra are generated using the Semiconductor Bloch Equations, demonstrating the importance of screening effects in shaping the optical response. The impact of the Brillouin zone sampling density on computational efficiency and spectral accuracy is systematically analysed and a minimum carrier density for the expectation of gain is quantified.
The third and final chapter combines insights gained in the previous two and proposes a theoretical nanolaser device consisting of a molybdenum disulfide monolayer integrated with a photonic crystal cavity. A material-oriented doublet-level formulation of the Quantum Laser Equations is developed to manage the multiscale dynamics, spanning femtosecond Coulomb processes to nanosecond lasing behaviour. The theory predicts electron-hole-plasma-based lasing at room temperature, characterised by an S-shaped input-output curve, hole burning at the K- and K′-valley, and spectral clamping. These features are indicative of lasing driven by plasma gain at high carrier densities and emerge naturally from the material-oriented quantum-optical treatment of the device.

Together, the three chapters establish a consistent, predictive, and microscopically realistic theoretical framework for semiconductor nanolasers. The developed models combine quantum-optical treatments with device-level properties focused on the utilised gain media, enabling a detailed understanding of the interplay between many-body physics and stimulated emission in nanoscale systems. These results contribute to the design of next-generation nanophotonic light sources and offer a pathway towards energy-efficient, on-chip integrated lasers suitable for future optical links and photonic computing platforms.