A. Thränhardt

Clustering effects in Ga(AsBi)

The photoluminescence from a Ga(AsBi) sample is investigated as a function of pump power and lattice temperature. The disorder-related features are analyzed using a Monte Carlo simulation technique. A two-scale approach is introduced to separately account for cluster localization and alloy disorder effects. The corresponding characteristic energy scales of 11 and 45 meV are deduced from the detailed comparison between experiment and simulation.

Nitrogen incorporation effects on gain properties of GaInNAs lasers: Experiment and theory

Gain properties of GaInNAs lasers with different nitrogen concentrations in the quantum wells are investigated experimentally and theoretically. Whereas nitrogen incorporation induces appreciable modifications in the spectral extension and the carrier density dependence of the gain, it is found that the linewidth enhancement factor is reduced by inclusion of nitrogen, but basically unaffected by different nitrogen content due to the balancing between gain and index changes.

Nonequilibrium gain in optically pumped GaInNAs laser structures

A theory is presented which couples a dynamical laser model to a fully microscopic calculation of scattering effects. Calculations for two optically pumped GaInNAs laser structures show how this approach can be used to analyze nonequilibrium and dynamical laser properties over a wide range of system parameters.

Microscopic theory of the optical properties of Ga(AsBi)/GaAs quantum wells

Optical gain and photoluminescence as well as radiative and Auger losses are calculated for Ga(AsBi)/GaAs quantum wells. The results are obtained using a consistent microscopic theory and an anticrossing model for the band structure. The influence of the band structure parameters on the optical properties is investigated.

Numerical study of the influence of an antireflection coating on the operating properties of vertical-external-cavity surface-emitting lasers

The influence of an antireflection coating on the input-output power characteristics and the switch-on dynamics of a vertical-external-cavity surface-emitting laser is investigated numerically with an effective rate-equation simulation based on microscopic many-body calculations for the optical gain/absorption and carrier losses. The simulations show a significantly higher threshold and a slower switch-on dynamics for the antireflection coated devices. These differences are caused by a reduction in the mode amplitude at the position of the active medium due to a less pronounced subcavity.

Luminescence dynamics in Ga(AsBi)

The temporal evolution of the spectrally resolved luminescence is measured for a Ga(AsBi) sample at low temperatures. The results are analyzed with the help of kinetic Monte Carlo simulations incorporating two disorder scales attributed to alloy disorder and Bi- clustering. An average time of 5 ps is identified as the upper limit for carrier capture into the Bi clusters whereas the extracted hopping rate associated with alloy fluctuations is much faster than the transitions between the individual cluster sites.

Dynamic behavior of 1040nm semiconductor disk lasers on a nanosecond time scale

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.

Microscopic calculation and measurement of the laser gain in a (GaIn)Sb quantum well structure

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.

Microscopic electroabsorption line shape analysis for Ga(AsSb)/GaAs heterostructures

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 str...

Type I-type II transition in InGaAs–GaNAs heterostructures

Optical interband transitions in a series of In0.23Ga0.77As–GaNxAs1−x quantum well samples are investigated. For changing nitrogen content, a type I-type II transition is identified by a detailed analysis of photoluminescence and photoreflectance spectra. Experimental results are compared systematically with spectra calculated by a microscopic theory. A valence band offset parameter of (1.5±0.5)eV is extracted for this heterostructure system.