ZnO nanorods as laser emitters

In the case of the semiconductor ZnO simple growth techniques exist that enable the self organized growth of a large variety of nanostructures. In this thesis ZnO nanorods, a certain kind of these structures, are investigated with respect to their suitability for lasing. In time-resolved photoluminescence measurements it is apparent that the quality of ZnO nanorods surpasses that of epitaxial layers as far as crystallinity and the density of defects are concerned. Under high optical excitation nanorods can show laser emission with the rods themselves acting as gain material as well as resonators. The threshold behavior as well as the temporal evolution of the laser emission of single rods is analyzed experimentally and numerically. The resonator properties of nanorods are evaluated within the framework of different models. Due to the nanoresonator 's low finesse the material gain has to be very large in order to achieve laser emission. In the face of that challenge the role of excitonic gain processes at room temperature is studied. In particular, the strength of the excitonphonon coupling is determined experimentally by measuring the broadening of the exciton luminescence. On account of the strong lateral confinement of light ZnO nanorods are good waveguides, which influences the laser emission profoundly. In order to assess the waveguiding properties of nanorods all guided modes of a hexagonal ZnO waveguide are calculated numerically. The influence of the waveguide structure on photoluminescence is not only evident in stimulated emission. In thin nanorods it also leads to a suppression of emission stemming from inelastic exciton-exciton-scattering. In addition to the waveguide modes' intensity distribution, the overlap with the gain medium and the modal gain are calculated. Based on these data the optimal nanorod geometry with respect to lasing is discussed.