Due to their small separation of longitudinal modes, Fabry-Pérot type laser diodes show rich mode competition effects. We present streak camera measurements of two nitride laser diodes with different cavity lengths and model them using a fully dynamic model based on the semiconductor Bloch equations, obtaining good agreement. Both theory and experiment show that the different mode spacing has a large influence on the interactions between longitudinal modes. In contrast to rate-equation type models, our approach includes the detailed density distribution as well as the derivation of the relevant parameters, e.g. broadening, from standard material quantities, thus setting a milestone on the way towards a fully predictive laser model.

The scattering and cooling dynamics in Ge quantum wells are investigated on a picosecond time scale. Time-resolved pump-probe experiments reveal an efficient scattering process between electrons in the L-valley and holes in the Γ-valley.

An efficient scattering process between the electron system in the L valley and the hole system in the Gamma valley in Ge/SiGe quantum wells is identified. Its dependencies on excitation energy and carrier density are analyzed using spectrally and time-resolved pump-probe experiments. This carrier scattering causes an ultrafast heating of the hole system leading to an additional bleaching signature appearing a few tens of picoseconds after the excitation. Our findings are supported by microscopic calculations of the absorption spectra for various carrier densities and temperatures based on the semiconductor Bloch equations. Additionally, this scattering mechanism explains the enhanced free carrier absorption observed in previously reported pump-probe experiments.

The novel semiconductor material Ga(AsBi) is investigated by the time-resolved photoluminescence as function of lattice temperature, excitation density, and excitation energy. Disorder and localization effects are found to strongly influence the spectra and the dynamics.

The influence of an intra-cavity anti-reflection coating on the switch-on dynamics and the power input-output characteristic of a vertical-external-cavity surface-en-fitting laser (VECSEL) system are investigated. The experiments show a significantly higher threshold and slower switch-on dynamics for anti-reflection coated systems. These differences originate in the changes in the mode strength at the active medium due to the more or less pronounced sub-cavity. The presented simulations based on microscopic calculations are in good qualitatively agreement with the experiments. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A detailed microscopic calculation and experimental measurements of the optical gain from a (GaIn)Sb structure are presented. For a given excitation density, the gain in the (GaIn)Sb material system considerably exceeds that of a comparable equivalent (GaIn)As∕GaAs structure. The physical reasons for this high gain are analyzed and attributed mostly to band structure effects.

The nanosecond dynamics of near-infrared semiconductor disk lasers is investigated experimentally and theoretically. Lasing and photoluminescence following barrier pumping are analyzed. Their spectral and temporal features such as luminescence overshoot and clamping, delay of lasing onset, and redshift of the emission are explained by a rate equation model taking into account the microscopic gain and luminescence. (c) 2007 American Institute of Physics.

We investigate a series of Ga(AsSb)/GaAs/AlGaAs quantum wells, that show an additional inplane confinement. This is attributed to the formation of self-organized GaAsSb quantum-islands during growth with confinement energies of several hundred meV.

Transient gain measurements are performed for (Galn)As quantum well structures. Gain up to 2000 cm-1 on a timescale of several hundred ps is observed. A microscopic model quantitatively provides theoretical support without introducing fit parameters.

We report on the lasing dynamics of semiconductor disk lasers following well and barrier pumping with both 500 ns and 5 mus pulses. The dynamics are explained using rate- equations.

A series of Ga(AsSb)∕GaAs∕(AlGa)As samples with varying GaAs spacer width are studied by electric-field modulated absorption (EA) and reflectance spectroscopy and modeled using a microscopic theory. The analysis of the Franz–Keldysh oscillations of GaAs capping layer and of the quantum-confined Stark shift of the lowest quantum well (QW) transitions shows the strong inhomogeneity of the built-in electric field indicating that the field modulation due to an external bias voltage differs significantly for the various regions of the structures. The calculations demonstrate that the line shape of the EA spectra of these samples is extremely sensitive to the value of the small conduction band offset between GaAs and Ga(AsSb) as well as to the magnitude of the internal electric field changes caused by the external voltage modulation in the QW region. The EA spectra of the entire series of samples are modeled by the microscopic theory. The good agreement between experiment and theory allows us to extract the strength of the modulation of the built-in electric field in the QW region and to show that the band alignment between GaAs and Ga(AsSb) is of type II with a conduction band offset of approximately 40 meV.

A dynamical laser model is coupled to a fully microscopic calculation of scattering rates. allowing efficient calculations without phenomenological parameters. The approach is used to analyze nonequilibrium effects in the switch-on of an optically pumped laser structure. Lasing leads to kinetic hole burning in both electron and hole distribution. The gain spectrum, however, does not show spectrally narrow hole burning but a reduction over a wide range of frequencies compared to the equilibrium gain because of the large homogeneous broadening in the high density lasing system.

Various samples from the GaInNAs dilute nitride material system are modeled microscopically and good agreement with experiment is shown for the optical gain, linewidth enhancement factor, photomodulated reflectance and photoluminescence. Even though the differential gain is reduced by the inclusion of nitrogen, the linewidth enhancement factor is shown to stay almost unchanged. Radiative decay times are calculated and show a strong change in their density dependence above threshold.

A brief overview of a consistent microscopic approach to model the optical and electronic properties of semiconductor nanostructures is presented. Coupled semiconductor Bloch and Maxwell equations are used to investigate the performance of semiconductor microcavity structures, photonic band gap systems, and lasers. The predictive potential of the microscopic theory is demonstrated for several examples of practical importance. Optical gain and output characteristics are computed for modern vertical external cavity surface emitting laser structures. It is shown how design flexibilities can be used to optimize the device performance. Nanostructures are proposed where semiconductor quantum wells are embedded in one-dimensional photonic crystals. For field modes spectrally below the photonic band edge it is shown that the optical gain and absorption can be enhanced by more than one order of magnitude over the value of the homogeneous medium. The increased gain can be used for laser action by placing quantum wells and a suitably designed photonic crystal structure inside a microcavity.