Ulrike Woggon

Exciton relaxation and dephasing in quantum-dot amplifiers from room to cryogenic temperature

We present an extensive experimental study of the exciton relaxation and dephasing in InGaAs quantum dots (QDs) in the temperature range from 10 K to 295 K. The QDs are embedded in the active region of an electrically pumped semiconductor optical amplifier. Ultrafast four-wave mixing and differential transmission spectroscopy on the dot ground-state transition are performed with a sensitive heterodyne detection technique. The importance of the population relaxation dynamics to the dephasing is determined as a function of injection current and temperature. Above 150 K dephasing processes much faster than the population relaxation are present, due to both carrier-phonon scattering and Coulomb interaction with the injected carriers. Only at low temperatures (<30 K) does population relaxation of multiexcitons in the gain regime fully determine the dephasing.

Electron microscopic and optical investigations of the indium distribution in GaAs capped InxGa1−xAs islands

Results from a structural and optical analysis of buried InxGa1−xAs islands carried out after the process of GaAs overgrowth are presented. It is found that during the growth process, the indium concentration profile changes and the thickness of the wetting layer emanating from a Stranski–Krastanow growth mode grows significantly. Quantum dots are formed due to strong gradients in the indium concentration, which is demonstrated by photoluminescence and excitation spectroscopy of the buried InxGa1−xAs islands.

Extended and localized photon states in 1D-coupled resonators

The evolution of individual microsphere-resonator modes into coherently coupled photon states is studied using polarization-sensitive imaging spectroscopy. Photon localization is found both due to Bloch-mode formation and size disorder in agreement with a coupled-oscillator model.

Extended and Localized Photon States in 1D-Coupled Resonators

The evolution of individual microsphere-resonator modes into coherently coupled photon states is studied using polarization-sensitive imaging spectroscopy. Photon localization is found both due to Bloch-mode formation and size disorder in agreement with a coupled-oscillator model.

Coupled-resonator optical waveguides (CROWs) doped with semiconductor quantum dots

We explore nanocrystal-doped microsphere resonators as building blocks for coupled-resonator optical waveguides. The evolution of waveguide modes is studied using polarization-sensitive microphotoluminescence spectroscopy. We demonstrate the formation of linear waveguides and light-bending resonator arrays.

Relaxation and dephasing of multiexcitons in electrically-pumped quantum dots

The population relaxation and dephasing of multiexcitonic transitions in InGaAs quantum dots embedded in the active region of an electrically-pumped semiconductor optical amplifier are measured in the temperature range from 10 K to 300 K.