arXiv subjects

A. Schliwa

Publications and source records attributed to A. Schliwa.

8 recordsLinked to original sources

arXiv2018

A deterministically fabricated spectrally-tunable quantum dot based single-photon source

Spectrally-tunable quantum-light sources are key elements for the realization of long-distance quantum communication. A deterministically fabricated single-photon source with a photon-extraction efficiency of η=(20 +- 2) % and a tuning range of ΔE=2.5 meV is presented here. The device consists of a single pre-selected quantum dot monolithically integrated into a microlens which is bonded onto a piezoelectric actuator via thermocompression goldbonding. The thin gold layer simultaneously acts as a backside mirror for the quantum dot emission, which is efficiently extracted from the device by an optimized lens structure patterned via 3D in-situ electron-beam lithography. The single-photon nature of the emission is proven by photon-autocorrelation measurements with $g^{(2)}$ (τ=0)=0.04 +- 0.02. The combination of deterministic fabrication, spectral-tunability and high broadband photon-extraction efficiency makes the microlens single-photon source an interesting building block towards the realization of quantum repeaters networks.

cond-mat.mes-hall↗

arXiv2010

Finite Element Simulation of the Optical Modes of Semiconductor Lasers

In the present article we investigate optical near fields in semiconductor lasers. We perform finite element simulations for two different laser types, namely a super large optical waveguide (SLOW) laser, which is an edge emitter, and a vertical cavity surface emitting laser (VCSEL). We give the mathematical formulation of the different eigenvalue problems that arise for our examples and explain their numerical solution with the finite element method. Thereby, we also comment on the usage of transparent boundary conditions, which have to be applied to respect the exterior environment, e.g., the very large substrate and surrounding air. For the SLOW laser we compare the computed near fields to experimental data for different design parameters of the device. For the VCSEL example a comparison to simplified 1D mode calculations is carried out.

physics.optics↗

arXiv2007

Polarized Emission Lines from Single InGaN/GaN Quantum Dots: Role of the Valence-band Structure of Wurtzite Group-III Nitrides

We present a study of the polarization properties of emission lines from single InGaN/GaN quantum dots (QDs). The QDs, formed by spinodal decomposition within ultra-thin InGaN quantum wells, are investigated using single-QD cathodoluminescence (CL). The emission lines exhibit a systematic linear polarization in the orthogonal crystal directions [1 1 -2 0] and [-1 1 0 0]--a symmetry that is non-native to hexagonal crystals. Eight-band k.p calculations reveal a mechanism that can explain the observed polarizations: The character of the hole(s) in an excitonic complex determines the polarization direction of the respective emission if the QD is slightly elongated. Transitions involving A-band holes are polarized parallel to the elongation; transitions involving B-type holes are polarized in the orthogonal direction. The energetic separation of both hole states is smaller than 10 meV. The mechanism leading to the linear polarizations is not restricted to InGaN QDs, but should occur in other wurtzite-nitride QDs and in materials with similar valence band structure.

cond-mat.mtrl-sci↗

arXiv2007

Polarized emission lines from A- and B-type excitonic complexes in single InGaN/GaN quantum dots

Cathodoluminescence measurements on single InGaN/GaN quantum dots (QDs) are reported. Complex spectra with up to five emission lines per QD are observed. The lines are polarized along the orthogonal crystal directions [1 1 -2 0] and [-1 1 0 0]. Realistic eight-band k.p electronic structure calculations show that the polarization of the lines can be explained by excitonic recombinations involving hole states which are either formed by the A or the B valence band.

cond-mat.mtrl-sci↗

arXiv2007

Control of fine-structure splitting and excitonic binding energies in selected individual InAs/GaAs quantum dots

A systematic study of the impact of annealing on the electronic properties of single InAs/GaAs quantum dots (QDs) is presented. Single QD cathodoluminescence spectra are recorded to trace the evolution of one and the same QD over several steps of annealing. A substantial reduction of the excitonic fine-structure splitting upon annealing is observed. In addition, the binding energies of different excitonic complexes change dramatically. The results are compared to model calculations within eight-band k.p theory and the configuration interaction method, suggesting a change of electron and hole wave function shape and relative position.

cond-mat.mtrl-sci↗

arXiv2006

Size-dependence of anisotropic exchange interaction in InAs/GaAs quantum dots

A comprehensive study of the exchange interaction between charge carriers in self-organized InAs/GaAs quantum dots is presented. Single quantum-dot cathodoluminescence spectra of quantum dots of different sizes are analyzed. Special attention is paid to the energetic structure of the charged excited exciton (hot trion). A varying degree of intermixing within the hot trion states leads to varying degrees of polarization of the corresponding emission lines. The emission characteristics change from circularly polarized for small quantum dots to elliptically polarized for large quantum dots. The findings are explained by a change of magnitude of the anisotropic exchange interaction and compared to the related effect of fine-structure splitting in the neutral exciton and biexciton emission.

cond-mat.mtrl-sci↗

arXiv2006

Ex-situ control of fine-structure splitting and excitonic binding energies in single InAs/GaAs quantum dots

A systematic study of the impact of annealing on the electronic properties of single InAs/GaAs quantum dots (QDs) is presented. We are able to record single QD cathodoluminescence spectra and trace the evolution of one and the same QD over several steps of annealing. A systematic reduction of the excitonic fine-structure splitting is reported. In addition the binding energies of different excitonic complexes change dramatically. The results are interpreted in terms of a change of electron and hole wavefunction shape and mutual position.

cond-mat.mtrl-sci↗

arXiv2006

Size-dependent fine-structure splitting in self-organized InAs/GaAs quantum dots

A systematic variation of the exciton fine-structure splitting with quantum dot size in single InAs/GaAs quantum dots grown by metal-organic chemical vapor deposition is observed. The splitting increases from -80 to as much as 520 $μ$eV with quantum dot size. A change of sign is reported for small quantum dots. Model calculations within the framework of eight-band k.p theory and the configuration interaction method were performed. Different sources for the fine-structure splitting are discussed, and piezoelectricity is pinpointed as the only effect reproducing the observed trend.

cond-mat.mtrl-sci↗