AbstractsPhysics

This Thesis provides an overview on microscopic theories for the description of semiconductor laser material systems. Therefore, it gives an overview about three theoretical models used for the description of different properties of semiconductors. First, an extension to the original Jaynes-Cummings model (JCM) is introduced. It is later used for the investigation of quantum dots hosting multiple electronic levels placed inside a microcavity. Advancing to a different approach, second, the semiconductor Bloch equations (SBEs) are discussed together with the system Hamiltonian and the resulting measurable macroscopic quantities, i.e. absorption and refractive index change. As third model, the semiconductor luminescence equations (SLEs) are presented to calculate photoluminescence (PL) spectra where the quantized properties of the light are taken into account. Last, the evaluation of photomodulated reflectance (PR) spectroscopy based on the SBEs is presented. Additionally, it reviews and extends all investigations made in the context of type-II band-aligned 'W'-systems. Besides the content presented in these publications, it starts with a general introduction of type-II and especially 'W'-aligned multiple quantum-well heterostructures (MQWHs). They are compared to traditional type-I systems in terms of temperature and charge carrier density dependence. The differences are studied based on the SBEs. Subsequently, as part of the closed-loop process, an experiment – theory comparison for PL measurements of epitaxially grown 'W'-MQWHs is presented. Based on the nominal parameters, i.e. quantum-well thickness and concentration, the material gain of this structure is computed. Excitonic transitions and their spatial recombination path are investigated to identify their type-II character. Subsequently, a systematic analysis of the 'W'-VECSEL sample is carried out. Here, charge carrier dependent reflection spectra are presented to confirm the experimentally determined lasing wavelength. The investigation of the VECSEL concludes with the determination of detuning and modal gain of the sample. In addition, optimization capabilities are discussed by the means of the carrier confinement due to graded interfaces and different barrier materials. As a last point, material compositions suitable to increase the emission wavelength to 1300 nm are suggested based on calculations. Unexpected oscillations in the emission of optically pumped semiconductor quantum-dot microcavities are discussed and analyzed. The usual linear slope of the I/O characteristics of this setup is modified. To figure out the origin of the nonlinearities, a systematic theoretical investigation is applied which identifies them as genuine quantum-memory effect. They are found to be directly … Advisors/Committee Members: Koch, Stephan W. (advisor).