1 Quantum Photonics, Department of Photonics Engineering, Technical University of Denmark2 Department of Photonics Engineering, Technical University of Denmark3 Nanophotonics Theory and Signal Processing, Department of Photonics Engineering, Technical University of Denmark4 Risø National Laboratory for Sustainable Energy, Technical University of Denmark
This thesis reports research on enhancement of light-matter interaction in semi- conductor quantum nanostructures by means of nanostructure fabrication, optical measurements, and theoretical modeling. Photonic crystal membranes of very high quality and samples for studies of quantum dots in proximity to semiconductor-air interfaces were fabricated. High- lights of the experiments performed on these samples include the rst quantitative comparison between measured exciton decay rates and the local density of opti- cal states in a photonic crystal membrane and the rst demonstration of radiative coupling between quantum dot excitons and a photonic crystal waveguide. We show theoretically that the dipole approximation is not valid a priori for quantum dots and wells in nanostructures. A many-particle exciton formalism is developed by which the Wigner-Weisskopf result for spontaneous emission is calculated beyond the dipole approximation. This is the rst rigorous derivation of such eects. Some highly non-trivial consequences are discussed. We introduce the semiconductor-air interface as an experimental tool to extract fundamental information about the decay dynamics of quantum dots. We compare experimental results to a detailed quantum dot model and nd good agreement. We use time-resolved spectroscopy on quantum wells near an interface to show that Coulomb eects dominate the dynamics of excitons in the well. Measurements of large quantum dots are compared to the theory of light-matter interaction beyond the dipole approximation, but the good agreement between experiment and dipole theory shows that the size of the eective connement potential in these quantum dots is much smaller than the quantum dot size rendering dipole theory valid. Finally, the strong coupling regime of light-matter interaction is investigated. For the rst time the vacuum Rabi splitting is observed in an electrically tunable device.