Sebastian Imhof

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.

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.

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.

Microscopic Modeling of Quantum Well Gain Media for VECSEL Applications

This paper summarizes a consistent microscopic approach that allows for predictive calculations of laser gain/absorption, photoluminescence, and the intrinsic laser loss processes. The theory is first evaluated for an (AlGaIn)As quantum well system used in a vertical-external-cavity surface-emitting laser structure. Good agreement with experimental results is demonstrated. In a second application, the microscopic approach is used to predict the optical properties of novel dilute bismide containing GaAs-based quantum well gain media. Modeling the bismuth-induced band structure modifications by a valence band anticrossing model, the material gain, radiative, and Auger losses are computed.

Bismuth-containing III–V semiconductors: Epitaxial growth and physical properties

The growth, surface, and bulk properties of GaAsBi and related III-V alloys are examined and the potential benefits of these materials are explored in terms of device applications. The methods used include molecular beam epitaxy growth, scanning tunneling microscopy, scanning electron microscopy, transmission electron microscopy, photoluminescence spectroscopy, deep-level transient spectroscopy, dynamic modeling, and theoretical analysis. The results show that considerable progress has been made in alloying bismuth with GaAs and that the structural, optical, and electronic quality is very good for the alloys investigated.

Optical spectroscopy of Bi containing semiconductors

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.