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  1. 108 Acta Physica Polonica A

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1
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Energy Spectrum of InAs Quantum Dots in GaAs/AlAs Superlattices

100%
Nedzinskas R., Čechavičius B., Kavaliauskas J., Karpus V., Krivaitė G., Tamošiūnas V., Valušis G., Schrey F., Unterrainer K., Strasser G.
Acta Physica Polonica A
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2008
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vol. 113
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issue 3
975-978
EN
Photo- and contactless electroreflectance spectroscopies were applied to study optical properties and electronic structure of GaAs/AlAs superlattice systems with embedded InAs quantum dots. The observed interband transitions related to the quantum dot ground and excited states, as well as optical transitions in the combined system formed by the InAs wetting layer and GaAs/AlAs superlattice are discussed.
2
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Two-Photon Coherent Polarization Flipping of Confined Excitons

100%
Machnikowski P.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
289-293
EN
A two-photon process leading to coherent transitions between the two circularly polarized exciton states in a quantum dot is studied. It is shown that optical flipping of the exciton polarization is possible with picosecond laser pulses. The process is closely related to two-photon Rabi oscillations of a biexciton but it is much more stable against shifts of the laser frequency.
3
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Hole Subband Mixing and Polarization of Luminescence from Quantum Dashes: A Simple Model

63%
Kaczmarkiewicz P., Musiał A., Sęk G., Podemski P., Machnikowski P., Misiewicz J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
633-636
EN
In this paper, we address the problem of luminescence polarization in the case of nanostructures characterized by an in-plane shape asymmetry. We develop a simple semi-qualitative model revealing the mechanism that accounts for the selective polarization properties of such structures. It shows that they are not a straightforward consequence of the geometry but are related to it via valence subband mixing. Our model allows us to predict the degree of polarization dependence on the in-plane dimensions of investigated structures assuming a predominantly heavy hole character of the valence band states, simplifying the shape of confining potential and neglecting the influence of the out-of-plane dimension. The energy dependence modeling reveals the importance of different excited states in subsequent spectral ranges leading to non-monotonic character of the degree of polarization. The modeling results show good agreement with the experimental data for an ensemble of InAs/InP quantum dashes for a set of realistic parameters with the heavy-light hole states separation being the only adjustable one. All characteristic features are reproduced in the framework of the proposed model and their origin can be well explained and understood. We also make some further predictions about the influence of both the internal characteristics of the nanostructures (e.g. height) and the external conditions (excitation power, temperature) on the overall degree of polarization.
4
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The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots

63%
Molas M., Gołasa K., Furman M., Lapointe J., Wasilewski Z., Potemski M., Babiński A.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
991-993
EN
Results of experimental study of multiexcitonic emission related to the p-shell of single self-assembled InAs/GaAs quantum dots are presented. Optical properties of a first emission line to appear from the p-shell of a strongly excited quantum dots are investigated using low-temperature polarization-sensitive micro-photoluminescence measurements. The emission line is attributed to the recombination of a complex of three electrons and holes confined in a dot (neutral triexciton), 3X. It is found that the emission consists of two linearly polarized components and the fine structure splitting is larger than the respective splitting of a neutral exciton. The optical anisotropy of the 3X emission is related to the anisotropy of the quantum dot localizing potential. The axis of the 3X optical anisotropy changes from dot to dot covering broad range within ± 50 degrees with respect to the axis defined by the optical anisotropy of a neutral exciton (X). Possible origin of the deviation is discussed.
5
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Influence of an Electric Field on Fine Properties of III-V and II-VI Quantum Dots Systems

63%
Kowalik K., Krebs O., Kudelski A., Golnik A., Lemaître A., Senellart P., Karczewski G., Kossut J., Gaj J., Voisin P.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
177-184
EN
We investigate the influence of an electric field on the optical properties of single quantum dots. For sample made of III-V compounds micron-size electro-optical structures were produced in order to apply an electric field in the dot plane. For several individual dots lines significant variations of the anisotropic exchange splitting with the field were observed. On sample made of II-VI compounds we demonstrate the influence of electric field fluctuations on the luminescence of a single quantum dot.
6
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Carrier Trapping in a Quantum Dash: Optical Signatures

63%
Kaczmarkiewicz P., Machnikowski P., Kuhn T.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
997-1000
EN
We theoretically study the optical properties and the electronic structure of highly elongated quantum dots (quantum dashes) and show how geometrical fluctuations affect the excitonic spectrum of the system. The dependence of the absorption intensities on the geometrical properties (depth and length) of the trapping center in a quantum dash is analyzed and the dependence of the degree of the linear polarization on these geometrical parameters is studied.
7
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Quantum Confinement in InAs/GaAs Systems with Self-Assembled Quantum Dots Grown Using In-Flush Technique

63%
Molas M., Kuldová K., Borysiuk J., Wasilewski Z., Babiński A.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
624-626
EN
The effect of In-flush technique application to the MBE-grown structure with self-assembled quantum dots is investigated in this work. The microphotoluminescence from structures with the InAs/GaAs dots grown with and without the In-flush has been investigated. We focus our attention on "not fully developed" dots, which can be clearly distinguished in the spectrum. The dots have also been identified in the transmission electron microscopy analysis of the structures. The In-flush does not influence a broad energy range of those features. Instead we have found that the anisotropic exchange energy splitting of neutral excitons confined in those in the structure grown with In-flush is substantially lower that the splitting in the structure with no In-flush. This observation confirms that the In-flush leads not only to better uniformity of self-assembled quantum dots but also to reduction of lateral potential, anisotropy, which is believed to result in the neutral exciton splitting.
8
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Optical Properties of CdTe QDs Formed Using Zn Induced Reorganization

63%
Kobak J., Pacuski W., Jakubczyk T., Kazimierczuk T., Golnik A., Frank K., Rosenauer A., Kruse C., Hommel D., Gaj J.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
627-629
EN
In this paper we present optical studies of CdTe quantum dots formed using Zn-induced reorganization. The pattern of quantum dot photoluminescence lines is found to be similar to typical results reported for quantum dots grown with other techniques, although the positively charged exciton line is relatively more pronounced. Also the energy spacing between biexciton and exciton lines is found to be larger than in typical results. Zn-induced reorganization results in quantum dots density higher by an order of magnitude than in Te-induced quantum dots.
9
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Photon Correlations and Cross-Correlations from a Single CdTe/ZnTe Quantum Dot

63%
Couteau C., Moehl S., Suffczyński J., Gaj J., Tinjod F., Gérard J., Kheng K., Mariette H., Romestain R., Poizat J.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
169-176
EN
We report correlation and cross-correlation continuous wave measurements in II-VI quantum dots grown by molecular beam epitaxy. Combination of spectral selection, saturation measurements and good temporal resolution allowed us to see an antibunching effect on photons from radiative recombination of excitons in a single CdTe/ZnTe quantum dot, as well as cross-correlation within the biexciton (X_{2})-exciton (X) radiative cascade from the same dot. We discuss the results of our experiments in terms of a model of excitonic multitransitions.
10
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Influence of Configuration Mixing on Energies and Recombination Dynamics of Excitonic States in CdTe/ZnTe Quantum Dots

63%
Smoleński T., Kazimierczuk T., Goryca M., Kossacki P., Gaj J., Wojnar P., Fronc K., Korkusiński M., Hawrylak P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
615-617
EN
We study experimentally and theoretically excitonic recombination processes in CdTe/ZnTe quantum dots. The single quantum dot photoluminescence spectrum was observed and emission lines from X, X^-, X^+ and 2X excitonic states were identified. Experimental results were analysed in the theoretical model based on the effective mass approximation. Numerical calculations of energy positions and recombination probabilities of X, X^-, X^+ and 2X were performed. Computed results reproduce correctly the order and relative positions of emission lines and ratios of radiative lifetimes.
11
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Four-Wave Mixing Spectroscopy of Quantum Dot Molecules

63%
Sitek A., Machnikowski P.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
167-172
EN
We study theoretically the nonlinear four-wave mixing response of an ensemble of coupled pairs of quantum dots (quantum dot molecules). We discuss the shape of the echo signal depending on the parameters of the ensemble: the statistics of transition energies and the degree of size correlations between the dots forming the molecules.
12
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Excitation Mechanisms of CdTe/ZnTe Quantum Dots under Non-Resonant and Quasi-Resonant Regime

63%
Kazimierczuk T., Gaj J., Golnik A., Goryca M., Nawrocki M., Koperski M., Smoleński T., Suffczyński J., Wojnar P., Kossacki P.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
588-591
EN
We discuss possible mechanisms of quantum dot population control. A set of experiments, including time-resolved photoluminescence, single photon correlations, excitation correlation, and photoluminescence excitation is used to determine the actual mechanism under non-resonant and quasi-resonant regime.
13
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Emission of Self-Assembled CdTe/ZnTe Quantum Dot Samples with Different Cap Thickness

63%
Nowak S.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
890-892
EN
Photoluminescence measurements on CdTe/ZeTe self-assembled quantum dot samples with different cap thickness values (18-110nm) were performed at 1.8 K at varying excitation levels. The shape of macrophotoluminescence spectra did not altered notably with the excitation power. The spectra exhibited interference fringes related to the total barrier thickness. Simulation of the fringes confirmed the barrier thickness determined during the growth. The minimal amplitude of the fringes was observed for the cap thickness corresponding approximately to a quarter of the emission wavelength in the barrier material. Maximum emission intensity occurred for the largest thickness of the cap, i.e., 110 nm. We attribute this result to the influence of the surface recombination centers.
14
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Properties of Excitons in Quantum Dots with a Weak Confinement

63%
Gołasa K., Molas M., Goryca M., Kazimierczuk T., Smoleński T., Koperski M., Golnik A., Kossacki P., Potemski M., Wasilewski Z., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
781-784
EN
Statistical properties of neutral excitons, biexcitons and trions confined to natural quantum dots formed in the InAs/GaAs wetting layer are reported. The correlation of the trion binding energy and the biexciton binding energy was found. Magnetospectroscopic measurements of the excitons revealed also the correlation of excitonic effective g^* factor of an exciton with the biexciton binding energy. The qualitative picture of the effect of quantum confinement on the observed correlations is presented.
15
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Anisotropic Exchange Interaction between p-Shell Electron and s-Shell Hole in CdTe/ZnTe Quantum Dots

63%
Kazimierczuk T., Golnik A., Goryca M., Wojnar P., Gaj J., Kossacki P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
882-884
EN
We study electron-hole exchange interaction in a single CdTe/ZnTe quantum dot by polarization-resolved photoluminescence measurements. We focus on recombination of excitonic states involving p-shell electrons: X^{2-} and XX^-. Recombination lines of X^{2-} and XX^- states exhibit fine structure, which can be consistently explained within a model with four parameters δ_{i}^{αβ} representing strength of iso- and anisotropic parts of interaction between s-hole and s- or p-electron.
16
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Control of Local Electric Fields Influencing the Photoluminescence οf an Individual CdTe/ZnTe Quantum Dot

63%
Haas K., Kazimierczuk T., Wojnar P., Golnik A., Gaj J., Kossacki P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
896-898
EN
We examine the influence of a weak non-resonant illumination on the quantum dot photoluminescence spectrum. We observe that even very weak illumination affects both intensity and spectral position of emission lines in the spectrum. We discover no significant asymmetry in spatial dependence and infer that the observed effects cannot be attributed to a single neighbor center.
17
Publication available in full text mode
Content available

Optical Properties of InAs Quantum Dots

63%
Willander M., Zhao Q., Jacob A., Wang S., Wei Y.
Acta Physica Polonica A
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2002
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vol. 102
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issue 4-5
567-576
EN
InAs quantum dots grown on GaAs substrate were investigated by optical spectroscopy. We particularly emphasized on the photoluminescence intensity, the stability of the photoluminescence intensity versus temperatures and wavelength of the InAs dot emission at various thermal treatments and different structures. We found that hydrogen can strongly passivate nonradiative centers without causing any structure degradation, and both n- and p-type modulation doping can reduce the decrease in the photoluminescence intensity when the sample temperature increases from the helium temperature to room temperature. The emission wavelength and the efficiency of the InAs quantum dots can also be manipulated by choosing proper materials of cap layer.
18
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The Phonon-Assisted Radiative Recombination of Excitons Confined in InAs Quantum Dashes

63%
Dusanowski Ł., Musiał A., Sęk G., Machnikowski P.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
813-816
EN
In this report we have investigated theoretically the phonon-assisted recombination process of excitons confined in strongly elongated semiconductor nanostructures, called quantum dashes. Interaction with phonon bath leads to the occurrence of phonon-assisted recombination, which in the case of acoustic phonons is manifested in the optical spectra as a deviation of the homogeneously broadened emission line shape from expected Lorentzian profile via occurrence of the so-called phonon sidebands. Hereby, we have modeled the influence of the quantum dash geometry on this spectral feature proving pronounced suppression of phonon-induced decoherence for strongly elongated nanostructures. Furthermore, the importance of different phonon coupling mechanisms has been evaluated and the spectral diffusion effects, unavoidable in the time-integrated photoluminescence experiments, have been accounted for.
19
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Time Evolution of the Microluminescence Energy οf GaN/AlGaN Quantum Dots

63%
Surowiecka K., Wysmołek A., Stępniewski R., Bożek R., Pakuła K., Baranowski J.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
933-935
EN
Time evolution of the microphotoluminescence from low-density GaN/Al_{x}Ga_{1-x}N quantum dots grown by metal organic chemical vapor deposition using in situ etching of AlGaN is presented. The observed effect is related to the energy changes that begin immediately after sample illumination with the exciting laser light and saturate after some time. Typically, the luminescence energy decreases and the change is exponential with characteristic times in a range between several dozen and several hundred seconds. However, sometimes we observed the energy increase with characteristic times in a range between several and a few hundred seconds. The obtained results are discussed in terms of the metastable change of the electric field, induced by spontaneous polarization present in GaN/AlGaN structure (in the growth direction), and strain- or defect-induced changes of the electric field in the vicinity of the dot.
20
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Content available

Spin-Dependent Coupling of Charged Quantum Dot Excitons with Continuum States

63%
Urbaszek B., Warburton R., Karrai K., Schulhauser C., Högele A., McGhee E., Govorov A., Gerardot B., Marie X., Amand T., Petroff P.
Acta Physica Polonica A
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2004
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vol. 106
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issue 3
395-402
EN
Magnetic field and temperature dependent photoluminescence studies on neutral and charged excitons in individual InAs quantum dots allow us to uncover different mechanisms by which the discrete quantum dot states are coupled to delocalized continuum states in a quantum well (the wetting layer). The behaviour of the neutral and singly charged excitons can be explained taking only discrete quantum dot states into account. For doubly and triply charged excitons we have to consider spin dependent coherent and incoherent interactions between discrete quantum dot states and delocalized wetting layer states.
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