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1
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Optical Spectroscopy of Quantum Dots in High Magnetic Fields

100%
Babiński A.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
275-286
EN
Optical spectroscopy measurements of single InAs/GaAs self-assembled quantum dots have been performed. The multiexcitonic emission from the s-, p-, and d-shells of a single dot is observed and investigated in magnetic field up to 28 T. The Zeeman splitting of the s-shell excitons has been found to depend on the dot morphology. While the energy-splitting in flat (2 nm height) dots linearly increases with magnetic field, its significant non-linearity is observed for larger in size, tall (4 nm height) dots. The effect of magnetic field on the orbital motion of carriers in dots has also been investigated. It has been found that the modified Fock-Darwin pattern explains the observed evolution of the emission from highly-excited single tall quantum dot.
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Electrical Properties of an Acceptor-like State of Metastable EL2 in n-type GaAs under Uniaxial Stress

64%
Babiński A., Wysmołek A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
908-910
EN
The electrical resistivity and deep level transient spectroscopy measurements of n-type GaAs under uniaxial stress for [100] and [111] directions at low temperatures are presented. After the transformation of EL2 to its metastable state the stress induced strong anisotropy in the increase in resistivity was observed. The observed splitting of the acceptor-like state of metastable EL2 implies the trigonal symmetry of that defect.
3
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Passivation of a Bulk Defect E_{c}-0.22 eV in GaAs by Contact with Phosphoric Acid

64%
Babiński A., Gołdys E.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
277-280
EN
The E_{c}-0.22 eV trap in Horizontal Bridgman undoped n-type GaAs may be passivated by contact with phosphoric acid for 8 hours at room temperature. Isochronal annealing, at around 250°C for 1 hour resulted in the partial recovery of this defect. The possible mechanisms of E_{c}-0.22 eV trap passivation are proposed.
4
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Orientation of Metastable EL2 under Uniaxial Stress

64%
Babiński A., Wysmołek A.
|
EN
Results of electrical resistivity and Hall measurements of n-type GaAs under uniaxial stress along [111] direction performed at low temperature are presented. Alter the transformation of the EL2 defect into its metastable configuration, a stress-induced increase in electrical resistivity related to the capture of electrons by the acceptor state of the metastable EL2([EL2*]^{-/0}) was observed. It was found that the stress-induced increase in resistivity depended on the method of EL2-photoquenching. The observed effects are explained as the reorientation of EL2* centers in the crystal. The stress coefficients of the triple degenerate and the single degenerate sublevels of the [EL2*]^{-/0} are found to be equal to -17 meV/GPa and -41 meV/GPa.
5
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Hydrostatic Pressure Spectroscopy of the Vanadium Luminescence in GaAs

52%
Wysmołek A., Bożek R., Babiński A., Hennel A.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
837-840
EN
We report luminescence measurements of the intracenter transition ^{3}T_{2} → ^{3}A_{2} of the V^{3+}(3d^{2}) charge state in semi-insulating GaAs under hydrostatic pressure up to 0.8 GPa at liquid helium temperature. The hydrostatic pressure coefficient of the zero-phonon line is found to be equal to 6.9 ± 0.2 meV/GPa. This result enables us to determine the Huang-Rhys parameter, which characterizes the coupling to the symmetric mode of vibration, as S_{A} = 1.4 ± 0.1. Using this parameter, computer simulation leading to a reconstruction of the shape of both luminescence and corresponding absorption spectra were performed.
6
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Influence of Intersubband Scattering on the Magnetic Field Dependence of the Conductivity Tensor

52%
Siwiec-Matuszyk J., Baj M., Babiński A., Kasprzak J.
Acta Physica Polonica A
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2006
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vol. 110
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issue 3
337-344
EN
In this paper we show that intersubband scattering can lead to apparent inconsistency of the experimental results obtained by means of classical and quantum transport measurements and this discrepancy is entirely connected with the usage of classical formulae to describe magnetic field dependence of a conductivity tensor. We prove that there is no contradiction in our observations and that the models describing quantum oscillations and magnetic-field dependence of the conductivity tensor, which are present in the literature, complement each other.
7
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Dynamics of Excitation Transfer Inside InAs/GaAs Quantum Dot System

52%
Korona K., Babiński A., Raymond S., Wasilewski Z.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
219-224
EN
We present time-resolved photoluminescence investigations of InAs/GaAs structures containing quantum dots with the ground state at 1.43 eV. State filling effect and a Pauli blocking effect were clearly observed. These effects significantly influenced dynamics of excitation transfer from upper to lower state inside a dot leading to non-exponential dynamics. Numerical model based on nonlinear rate equations was proposed. The model described well the experimental data providing values of: lifetime of the ground state 0.53±0.03 ns, lifetime of excited state (when the ground state is full) 1.1±0.2 ns, and internal relaxation time (when the ground state is empty) 0.07±0.01 ns.
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Intershell Exchange Interaction in Charged GaAlAs Quantum Dots

52%
Molas M., Nicolet A., Potemski M., Babiński A.
Acta Physica Polonica A
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2013
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vol. 124
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issue 5
785-787
EN
Optical anisotropy of charged excitons and biexcitons related to the single-particle s- and p-shell emission in GaAlAs/AlAs quantum dots is investigated. The polarization-dependence and time-resolved micro-photoluminescence measurements were performed. Cross-correlation measurements were used to identify the ladder of excitonic states and allowed us to show two cascade pathways, including the spin singlet and triplet states of charged excitons and biexcitons. The fine structure of the studied states is described and analysed in terms of electron-electron, hole-hole, and electron-hole exchange interactions.
9
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Deep Level Transient Spectroscopy Measurements of an Acceptor-like State of Metastable EL2 in GaAs and GaAsP

52%
Babiński A., Wysmołek A., Słupiński T.
Acta Physica Polonica A
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1993
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vol. 84
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issue 4
673-676
EN
The results of deep level transient spectroscopy measurements of an acceptor-like state of metastable EL2 in GaAs and GaAs_{0.97}P_{0.03} are presented. The uniaxial stress in GaAs was applied in order to find the deep leve1 transient spectroscopy signal. It was found that the deep level transient spectroscopy signal depended on the stress direction. In GaAs_{0.97}P_{0.03} the deep level transient spectroscopy peak related to an acceptor-like state of metastable EL2 was observed without external stress.
10
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Dynamics of Photoexcited Carriers in GaInAs/GaAs Quantum Dots

52%
Ilczuk E., Korona K., Babiński A., Kuhl J.
Acta Physica Polonica A
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2001
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vol. 100
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issue 3
379-386
EN
We present photocurrent and time-resolved photoluminescence investigations of AlGaAs/GaInAs/GaAs structures containing GaInAs/GaAs self-assembled quantum dots. The high electrical field in those devices significantly influences carrier dynamics. The photocurrent spectra show a double peak with maxima at 1.40 and 1.47 eV (at 80 K). These maxima are due to the GaInAs wetting layer (higher) and the quantum dots (lower). The photoluminescence spectra comprise weak excitonic luminescence from GaAs at 1.504 eV (at 80 K) and stronger and broad emission from the Ga_{0.4}In_{0.6}As quantum dots. At 300 K, the quantum dots emission has a lifetime of 1.1 ns and has a maximum at an energy of 1.38 eV. By analysis of both experiments, we can separate the influence of different radiative and nonradiative recombination processes. So, the tunneling rate: r_T=0.5 ns^{-1} and the radiative recombination rate in the quantum dots: r_{RQD}=0.4 ns^{-1} have been determined. The high tunneling probability (due to the influence of the built-in electric field) reveals that the tunneling effect is important for the recombination and transport processes in our structures.
11
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The Pressure Dependence of Transition Metal-Related Levels in GaAs

52%
Babiński A., Baj M., Hennel A.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
323-327
EN
The hydrostatic pressure coefficients of V^{3+/2+} acceptor level in bulk GaAs and of the 0.48 eV trap (related to Ni^{2+/1+} double acceptor level) in VPE GaAs were measured by means of the DLTS technique. The obtained values are 94 meV/GPa and 196 meV/GPa relative to the bottom of the conduction band. For Ni^{2+/1+} level the strong pressure dependence of the capture cross-section activation energy (60 meV/GPa) was also observed.
12
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Acceptor-Like Level of the EL2 Defect in its Metastable Configuration

52%
Dreszer P., Baj M., Babiński A.
Acta Physica Polonica A
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1991
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vol. 79
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issue 1
129-132
EN
This paper presents for the first time the evident experimental confirmation that EL2 defect, while being in its metastable configuration, traps under hydrostatic pressure an additional electron, i.e. the acceptor-like (EL2*)^{0/-} level enters the energy gap under pressure. We propose that in n-GaAs the EL2 thermal recovery takes always place via the (EL2*)^{-} state.
13
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Magnetic Field Effect on the Excitation Spectrum of a Neutral Exciton in a Single Quantum Dot

45%
Molas M., Nicolet A., Piętka B., Babiński A., Potemski M.
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vol. 126
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issue 5
1066-1068
EN
Excitation-energy-dependent magnetospectroscopic measurements of a single GaAlAs/AlAs quantum dot were performed. A significant effect of the excitation energy on the photoluminescence spectra is reported. The photoluminescence excitation spectroscopy has been used to investigate the excitation spectrum of a single electron-hole pair - a neutral exciton in magnetic field up to 14 T. The observed resonances exhibit diamagnetic shift characteristic of an s-shell related emission. In our opinion, the creation of excited complexes involving an excited hole and a ground electron is responsible for the process.
14
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Fine Structure of Neutral Excitons in Single GaAlAs Quantum Dots

45%
Molas M., Gołasa K., Piętka B., 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
988-990
EN
Optical anisotropy of neutral excitons in GaAlAs/AlAs quantum dots is investigated. Low-temperature polarization-sensitive photoluminescence measurements of single quantum dots are performed. It is found that neutral excitons (X) in the quantum dots exhibit a fine structure splitting. The fine structure splitting ranges from 10 μeV to 100 μeV and correlates with the X energy. The polarization axis of the fine structure splitting is well oriented along [110] crystallographic direction of a substrate. The orientation is attributed to the elongation of GaAlAs/AlAs quantum dots in the [110] direction of the substrate.
15
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Quantum Confinement in InAs/GaAs Systems with Self-Assembled Quantum Dots Grown Using In-Flush Technique

45%
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.
16
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Confocal Microscope Studies of MoS_{2} Layer Thickness

45%
Grzeszczyk M., Gołasa K., Piętka B., Babiński A., Szczytko J.
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vol. 126
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issue 5
1207-1208
EN
We have been studying micro-luminescence of various exfoliated MoS_{2} flakes using a confocal microscope. A crucial issue is to determine thickness of the investigated layer. The common way - using atomic force microscopy, electron microscopy or the Raman spectroscopy - requires moving the sample out from the confocal microscope experimental setup and looking for a particular exfoliated flake hidden among thousands of others. In order to preliminarily determine thickness of investigated layers we have performed a study on optical reflectivity and compared the results with the Raman spectroscopy investigations. In this way we were able to calibrate our experimental setup. Optical measurements are much faster than the Raman spectroscopy and can give a good estimation of MoS_{2} thickness.
17
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FFirst TSC and DLTS Measurements of Low Temperature GaAs

39%
Muszalski J., Babiński A., Korona K., Kamińska E., Piotrowska A., Kamińska M., Weber E.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
413-416
EN
The first thermally stimulated current (TSC) and deep level transient spectroscopy (DLTS) studies performed on GaAs grown by molecular beam epitaxy (MBE) at low substrate temperatures (LT GaAs) are reported. TSC experiments, conducted on as grown and 400-580°C annealed layers showed domination of arsenic antisite (EL2-like) defect and supported its key role in hopping conductivity. DLTS studies, performed on Si doped and annealed at 800°C layers revealed substantially lower concentration of EL2-like defect and an electron trap of activation energy ΔE = 0.38 eV was found.
18
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Hydrostatic-Pressure Deep Level Transient Spectroscopy Study of the Heteroantisite Antimony Level in GaAs

39%
Babiński A., Przybytek J., Baj M., Omling P., Samuelson L., Słupiński T.
Acta Physica Polonica A
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1992
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vol. 82
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issue 5
841-844
EN
We present some preliminary results of the first hydrostatic-pressure study of the electronic level related to the Sb-heteroantisite defect in GaAs. We studied two kinds of n-type GaAs samples doped with antimony: bulk samples grown by liquid encapsulated Czochralski method and thin layers grown by metalorganic chemical vapour deposition technique. We found strongly nonlinear pressure dependence of the activation energy of the emission rate for the level. Moreover, the results obtained for the bulk material were fairly different from those obtained for thin metalorganic chemical vapour deposition layers. The possible explanation of this difference is presented.
19
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The Fine Structure of a Triexciton in Single InAs/GaAs Quantum Dots

39%
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.
20
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The Effect of Substrate on Vibrational Properties of Single-Layer MoS₂

39%
Gołasa K., Molas M., Nogajewski K., Grzeszczyk M., Zinkiewicz M., Potemski M., Babiński A.
Acta Physica Polonica A
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2016
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vol. 130
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issue 5
1172-1175
EN
We report on the Raman scattering from single-layer molybdenum disulfide (MoS₂) deposited on various substrates: Si/SiO₂, hexagonal boron nitride (h-BN), sapphire, as well as suspended. Room temperature Raman scattering spectra are investigated under both resonant (632.8 nm) and non-resonant (514.5 nm) excitations. A rather weak influence of the substrate on the Raman scattering signal is observed. The most pronounced, although still small, is the effect of h-BN, which manifests itself in the change of energy positions of the E' and A'₁ Raman modes of single-layer MoS₂. We interpret this modification as originating from van der Waals interaction between the MoS₂ and h-BN layers.
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