Search results

1

Lateral Spin Diffusion Probed by Two-Color Hanle-MOKE Technique

100%

Quast J., Astakhov G., Ossau W., Molenkamp L., Heinrich J., Höfling S., Forchel A.

Acta Physica Polonica A

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2008

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vol. 114

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issue 5

1311-1316

EN

We report on all optical spatially resolved spin diffusion experiments in an unstrained, unbiased n-GaAs layer. Optical pump and probe intensities are varied over a wide range to study the impact of optical disturbance on spin transport. Both quantities have a considerable influence on the measured spin diffusion length and spin lifetime. Furthermore, an effective spin diffusion coefficient was obtained as a function of temperature.

2

Influence of Built-in Electric Field on Forbidden Transitions in In_xGa_{1-x}As/GaAs Double Quantum Well by Three-Beam Photoreflectance

100%

Sęk G., Ryczko K., Misiewicz J., Bayer M., Wang T., Forchel A.

Acta Physica Polonica A

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2001

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vol. 100

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issue 3

417-424

EN

Photoreflectance spectroscopy has been used to study optical transitions in In_{0.045}Ga_{0.955}As/GaAs double quantum well at 80 K. The derivative nature of this contactless electromodulation technique allows for the observation of excited state transitions in the low-dimensional structure including the symmetry-forbidden ones. Excitonic symmetry-forbidden transitions can be observed due to the effect of mixing of heavy and light hole excitons and/or due to some asymmetry in the structure. We have shown that the built-in electric field in the region of double quantum well is weak enough (less than 0.5 kV/cm) not to cause any significant energetic shift of features due to quantum confined Stark effect, on one hand. On the other hand, it is sufficient to change strongly the oscillator strength of forbidden transitions. To change the internal electric field, we have used photoreflectance in the three-beam mode with a third beam continuously illuminating the sample and causing changes of the built-in electric fields due to the photovoltage effect. This method works as a contactless forward bias and allows for a change of the field down to the flat band conditions. We have shown that changes of built-in electric field by amount of a few tenths of kV/cm can modify the intensity of forbidden transitions significantly. We show that, although the mixing of excitons is still important, a very weak built-in electric field can be dominant in the observation of forbidden excitonic transitions in double quantum well.

3

Nano-Optics on Individual Quantum Objects - From Single to Coupled Semiconductor Quantum Dots

84%

Bacher G., Schömig H., Welsch M., Scheibner M., Seufert J., Obert M., Forchel A., Maksimov A., Zaitsev S., Kulakovskii V.

Acta Physica Polonica A

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2002

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vol. 102

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issue 4-5

475-494

EN

Some recent highlights of our optical studies on single and coupled semiconductor quantum dots are reviewed. In the first part, we concentrate on the role of spins and spin-spin interaction in nonmagnetic and magnetic single quantum dots. In the case of strictly resonant excitation of the ground state in self-assembled CdSe/ZnSe quantum dots, we find an exciton spin relaxation time, which exceeds the recombination lifetime significantly. Linear polarization has to be used for these experiments, as the electron-hole exchange interaction lifts the spin degeneracy and the eigenstates are linear combinations of spin-up and spin-down excitons. In a magnetic quantum dot, the exchange interaction between carrier spins and the spins of magnetic ions is shown to be responsible for giant magneto-optical effects. We demonstrate the formation of zero-dimensional magnetic polarons and we succeeded in measuring the magnetization on a scale of a few nanometers using the characteristic photoluminescence signal of individual quantum dots as experimental monitor. The second part is devoted to pairs of single quantum dots. On one hand, single exciton tunneling within an individual quantum dot pair is demonstrated studying single pairs of vertically correlated strain-induced and self-organized quantum dots. On the other hand, we show that in a pair of lithographically defined single dots with strongly different g-factors the energy spacing between the dot ground states can be tuned in an external magnetic field by about 10 meV, giving access to a controlled coupling between two individual quantum dots.

4

GaAs-Based Quantum Well Exciton-Polaritons beyond 1 μm

84%

Pieczarka M., Podemski P., Musiał A., Ryczko K., Sęk G., Misiewicz J., Langer F., Höfling S., Kamp M., Forchel A.

Acta Physica Polonica A

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2013

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vol. 124

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issue 5

817-820

EN

Realization of the Bose-Einstein condensate can provide a way for creation of an inversion-free coherent light emitter with ultra-low threshold power. The currently considered solutions provide polaritonic emitters in a spectral range far below 1 μm limiting their application potential. Hereby, we present optical studies of InGaAs/GaAs based quantum well in a cavity structure exhibiting polaritonic eigenmodes from 5 to 160 K at a record wavelength exceeding 1 μm. The obtained Rabi splitting of 7 meV was almost constant with temperature, and the resulting coupling constant is close to the calculated QW exciton binding energy. This indicates the very strong coupling conditions explaining the observation of polaritons at temperatures where the exciton dissociation is already expected, and allows predicting that room temperature polaritons could still be formed in this kind of a system.

5

Effect of Confinement Anisotropy on Excitonic Properties in InAs/InP Quantum Dashes

84%

Mrowiński P., Musiał A., Sęk G., Misiewicz J., Höfling S., Somers A., Hein S., Forchel A.

Acta Physica Polonica A

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2013

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vol. 124

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issue 5

801-804

EN

The influence of confinement potential anisotropy on emission properties of strongly elongated single InAs/InGaAlAs/InP quantum dashes has been investigated by polarization-resolved microphotoluminescence spectroscopy at around 1.5 μm. There have been determined the exciton fine structure splitting, degree of linear polarization of surface emission and biexciton binding energy. The investigated dashes exhibited usually: the exciton anisotropy splitting larger than 100 μeV, the corresponding biexciton binding energy of about 3 meV, and the degree of linear polarization values in the range from 24% to 55%. Here, we presented a correlation of these parameters for several quantum dashes, which can be attributed either to a change in lateral aspect ratio within the ensemble, or the carrier localization on random fluctuations of the dash confinement potential.

6

Temperature Dependence of Photoluminescence from Epitaxial InGaAs/GaAs Quantum Dots with High Lateral Aspect Ratio

84%

Musiał A., Sęk G., Maryński A., Podemski P., Misiewicz J., Löffler A., Höfling S., Reitzenstein S., Reithmaier J., Forchel A.

Acta Physica Polonica A

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2011

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vol. 120

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issue 5

883-887

EN

Hereby, we present a study of a thermal quenching of emission from self-assembled epitaxial highly asymmetric quantum dots in InGaAs/GaAs material system for both ensemble and single dot regime. Pronounced interplay between the intensity of wetting layer and quantum dots originated emission was observed as the temperature was increased, evidencing a thermally activated energy transfer between the two parts of the system and an important role of the wetting layer in determining the optical properties of these anisotropic nanostructures. The carrier activation energies have been derived and possible carrier loss mechanisms have been analyzed. Single dot study revealed activation energies slightly varying from dot to dot due to size and shape distribution. The problem of the shape uniformity of individual quantum dot has also been addressed and possibility of additional carrier localization within the investigated structures has been found to be insignificant based on the recorded spectroscopic data.

7

Semiconductor Cavity Quantum Electrodynamics with Single Quantum Dots

68%

Reitzenstein S., Schneider C., Münch S., Kistner C., Strauss M., Huggenberger A., Franeck P., Weinmann P., Kamp M., Höfling S., Worschech L., Forchel A.

Acta Physica Polonica A

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2009

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vol. 116

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issue 4

445-450

EN

This paper summarizes recent progress achieved in the field of semiconductor cavity quantum electrodynamics with single quantum dots with the focus being on micropillar cavities. Light-matter interaction both in the strong and weak coupling regime is presented. Resonance tuning of the quantum dot by temperature, electric fields and magnetic fields is demonstrated while the strong coupling regime can be reached. Additionally, deterministic device integration of single positioned quantum dots is reported by a combination of site controlled quantum dot growth via directed nucleation and subsequent device alignment to overcome the degree of randomness of the quantum dot position in so far most common quantum dot-cavity systems.

8

Effect of Hydrogen on the Electronic Properties of GaAs_{1-y}N_y Heterostructures

68%

Bissiri M., Gaspari V., Baldassarri H. v. H. G., Ranalli F., Polimeni A., Capizzi M., Nucara A., Geddo M., Fischer M., Reinhardt M., Forchel A.

Acta Physica Polonica A

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2001

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vol. 100

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issue 3

365-371

EN

We have performed photoluminescence measurements in order to study the optical properties of hydrogenated GaAs_{1-y}N_y/GaAs heterostructures for y ranging from 0 to 0.03. Hydrogen irradiation leads to: (i) a progressive passivation of N-related recombination lines for low N content (y≈ 0.001); (ii) a sizable blue shift of the band gap in the "alloy" limit (y≈0.01). Thermal annealing restores the optical properties samples had before hydrogenation. These results can be accounted for by the formation of N^- -H^+ complexes and demonstrate that hydrogen irradiation provides a powerful tool for the analysis of photoluminescence spectra of GaAs_{1-y}N_y.

9

Hydrogen Tuning of (InGa)(AsN) Optical Properties

68%

Baldassarri H. v. H. G., Ranalli F., Bissiri M., Gaspari V., Polimeni A., Capizzi M., Nucara A., Geddo M., Fischer M., Reinhardt M., Forchel A.

Acta Physica Polonica A

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2001

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vol. 100

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issue 3

373-378

EN

The effects of atomic hydrogen irradiation on the optical properties of (InGa)(AsN) single quantum wells investigated by means of photoluminescence spectroscopy. For increasing hydrogen dose, the photoluminescence band peak energy of each nitrogen-containing sample blue-shifts and for high hydrogen dose it reaches that of a corresponding nitrogen-free reference sample. This effect is accompanied by a broadening of the photoluminescence band line width and by a decrease in the photoluminescence efficiency. Thermal annealing at 550ºC fully restores the original band gap value and the photoluminescence line width of the sample before hydrogenation. An interpretation of these phenomena is proposed in terms of an H perturbation of the charge distribution around the strongly electronegative N atoms, leading most likely to the formation of H-N complexes, and to an ensuing electronic passivation of nitrogen.

Refine search results

Lateral Spin Diffusion Probed by Two-Color Hanle-MOKE Technique

Influence of Built-in Electric Field on Forbidden Transitions in In_xGa_{1-x}As/GaAs Double Quantum Well by Three-Beam Photoreflectance

Nano-Optics on Individual Quantum Objects - From Single to Coupled Semiconductor Quantum Dots

GaAs-Based Quantum Well Exciton-Polaritons beyond 1 μm

Effect of Confinement Anisotropy on Excitonic Properties in InAs/InP Quantum Dashes

Temperature Dependence of Photoluminescence from Epitaxial InGaAs/GaAs Quantum Dots with High Lateral Aspect Ratio

Semiconductor Cavity Quantum Electrodynamics with Single Quantum Dots

Effect of Hydrogen on the Electronic Properties of GaAs_{1-y}N_y Heterostructures

Hydrogen Tuning of (InGa)(AsN) Optical Properties