A. Chernikov

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.

High-Power Optically Pumped Semiconductor Laser at 1040 nm

We demonstrate near-diffraction limited (M 2 ¿ 1.5) output up to 23.8 W with optical-to-optical efficiency 27% and slope efficiency 32.4% and 40.7 W of multimode output from an optically pumped semiconductor laser at 1040 nm. Temperature-dependent photoluminescence measurements confirm accurate epitaxial growth according to the design thereby enhancing the effective gain.

Heat Management in High-Power Vertical-External-Cavity Surface-Emitting Lasers

The thermal properties of a high-power vertical-external-cavity surface-emitting laser (VECSEL) are studied experimentally, focusing on the generation, distribution, and removal of excess heat under extreme pumping conditions. Different heat-spreading and heat-transfer approaches are analyzed. The performance of the device is optimized yielding a maximum emitted power beyond 70 W from a single spot. Finally, the potential for power-scaling in VECSELs and its restrictions are examined.

Influence of the spatial pump distribution on the performance of high power vertical-external-cavity surface-emitting lasers

The performance of a 1040 nm vertical-external-cavity surface-emitting laser is studied as function of the size and shape of the pumped area. The input-output characteristics of the device are monitored while simultaneously tracking the temperature in the active region. It is shown that the pump spot shape plays a crucial role in optimizing the laser output. Improvements up to a factor of 5 are found for a super-Gaussian in comparison to the standard Gaussian shape. For the large pump-spot sizes needed for high output powers, it turns out that the power-scalability breaks down due to the suppressed lateral heat flow.

Quantitative study of localization effects and recombination dynamics in GaAsBi/GaAs single quantum wells

Localization effects on the optical properties of GaAs1−xBix/GaAs single quantum wells (SQWs), with Bi contents ranging from x = 1.1% to 6.0%, are investigated using continuous-wave and time-resolved photoluminescence. The temperature- and excitation density dependence of the PL spectra are systematically studied, and the carrier recombination mechanisms are analyzed. At low temperatures, the time-integrated PL emission is dominated by the recombination of localized electron-hole pairs due to the varying content and clustering of Bi in the alloy. The extracted energy scales fluctuate tremendously when the Bi content is varied with a weak tendency to increase with Bi content. Relatively low energy scales are found for the SQW with x = 5.5%, which makes it a potential candidate for long-wavelength optoelectronic devices.

Photoluminescence decay of direct and indirect transitions in Ge/SiGe multiple quantum wells

We present a detailed experimental study of the photoluminescence decay of direct Γ-Γ and indirect L-Γ transitions in compressively strained Ge/Si0.15Ge0.85 type I multiple quantum wells. The lifetime of the fundamental L-Γ indirect-gap related transition is in the 6 to 13 ns range at the lattice temperature of 14 K. These values are just one order of magnitude higher than those typical of type-I direct gap III-V quantum wells and are significantly shorter than those characteristic of type-II indirect gap SiGe/Si quantum wells. The measured decay times show a clear dependence on the quantum well width and lattice temperature. The decay of the Γ-Γ direct-gap related transition is dominated by the ultrafast electron scattering from Γ-type to L-type states of the conduction band.

Exciton confinement in homo- and heteroepitaxial ZnO/Zn1 − xMgxO quantum wells with x < 0.1

ZnO/Zn1 − xMgxO single quantum well (SQW) structures with well widths dW between 1.1 nm and 10.4 nm were grown by plasma-assisted molecular beam epitaxy both heteroepitaxially on c-plane sapphire and homoepitaxially on (0001¯)-oriented bulk ZnO. A significantly reduced Mg incorporation in the top barrier related to the generation of stacking faults is observed for heteroepitaxial samples. Exciton localization is observed for both types of samples, while an enhancement of the exciton binding energy compared to bulk ZnO is only found for homoepitaxial SQWs for 2 nm ≤ dW ≤ 4 nm. Consistently, for homoepitaxial samples, the carrier dynamics are mainly governed by radiative recombination and carrier cooling processes at temperatures below 170 K, whereas thermally activated non-radiative recombination dominates in heteroepitaxial samples. The effects of polarization-induced electric fields are concealed for Mg concentrations x < 0.1 due to the reduction of the exciton binding energy, the screening by residual c...

Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells

W. D. Rice, J. Kono,1,2,∗ S. Zybell, S. Winnerl, J. Bhattacharyya, H. Schneider, M. Helm, B. Ewers, A. Chernikov, M. Koch, S. Chatterjee, G. Khitrova, H. M. Gibbs,†,6 L. Schneebeli, B. Breddermann, M. Kira, and S. W. Koch, Department of Electrical and Computer Engineering, Rice University, Houston, Texas 77005, USA Department of Physics and Astronomy, Rice University, Houston, Texas 77005, USA Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, D-01314 Dresden, Germany Technische Universität Dresden, 01062 Dresden, Germany Department of Physics, Philipps University Marburg, Renthof 5, D-35032 Marburg, Germany College of Optical Science, University of Arizona, Tucson, Arizona 85721-0094, USA ∗corresponding author: kono@rice.edu

Time-dynamics of the two-color emission from vertical-external-cavity surface-emitting lasers

The temporal stability of a two-color vertical-external-cavity surface-emitting laser is studied using single-shot streak-camera measurements. The collected data is evaluated via quantitative statistical analysis schemes. Dynamically stable and unstable regions for the two-color operation are identified and the dependence on the pump conditions is analyzed.

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.