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  1. 87 Wojtowicz T.

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1
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Doping and Characterization of Wide-Gap II-VI Epilayers

100%
Karczewski G., Wojtowicz T.
Acta Physica Polonica A
|
1996
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vol. 90
|
issue 4
635-644
EN
In this paper we review the properties of n-type doped ZnSe and CdTe epilayers grown by molecular beam epitaxy on (100) GaAs substrates. Recent results of photoluminescence, transport measurements, secondary ion mass spectroscopy and deep-level transient spectroscopy are discussed. A major emphasis is placed on the effect of different dopant species and the role of the deviation from stoichiometry on the doped epitaxial layers. Since deep defect states play an important role in determining the properties of the doped materials, considerable attention is directed towards characterization and identification of deep-lying defect states, both native and introduced by dopants. In particular, in the case of ZnSe the deep-level transient spectroscopy results clarify why Cl is superior to Ga as an effective n-type dopant. They provide strong evidence that chlorine - unlike Ga - does not introduce by itself any detectable deep defects into the ZnSe lattice. In the case of CdTe, we focus on the influence of the deviation from stoichiometric growth conditions in the molecular beam epitaxy process and on the properties of In doped layers. We discuss resistivity, Mn diffusivity and the presence of various deep defects in layers grown at different Cd/Te flux ratios.
2
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Stimulated and Laser Emission in CdZnTe/CdMnTe Double Quantum Well Heterostructures

81%
Kowalczyk L., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
787-790
EN
Stimulated emission by optical excitation has been investigated in CdZnTe/CdMnTe quantum well heterostructures. Laser action has been achieved at 4.2 K and at 77 K with relatively low threshold values of the excitation intensity. Photοluminescence excitation spectra of the stimulated emission were obtained indicating that the optical gain involves exciton-exci­ton inelastic scattering.
3
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Application of Photomemory Effect in Cd_{1-x}Mn_{x}Te_{1-y}Se_{y}:In for Direct Measurements of Magnetization of Bound Magnetic Polarons

81%
Wojtowicz T., Koleśnik S., Miotkowski I., Furdyna J.
Acta Physica Polonica A
|
1992
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vol. 82
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issue 4
637-640
EN
The first direct measurement of the magnetization of donor bound magnetic polarons in diluted magnetic semiconductors is reported. The experiment has been performed taking advantage of photomemory effect found in n-type Cd_{1-x}Mn_{x}Te_{1-y}Se_{y} crystals doped with In. Good agreement between experimental results and theory of bound magnetic polarons is observed.
4
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Changing the Properties of the CdTe/ZnTe Quantum Dots by in situ Annealing during the Growth

81%
Wojnar P., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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2007
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vol. 112
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issue 2
283-288
EN
We present an attempt to control the properties of CdTe/ZnTe self-assembled quantum dots during their formation in the process of molecular beam epitaxy. Namely, the structures were in situ annealed at various temperatures and annealing times after the formation of quantum dots, before the deposition of a capping layer. Depending on the annealing parameters, the dots exhibit different optical properties which were studied by means of spatially resolved photoluminescence. From the analysis of these results, the information about relative changes of the average size and sheet density of quantum dots was extracted.
5
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Electrical Properties of p-ZnTe/n-CdTe Photodiodes

81%
Chusnutdinow S., Makhniy V., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2012
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vol. 122
|
issue 6
1077-1079
EN
Current-voltage (I-V) and capacitance-voltage (C-V) characteristics of photovoltaic, thinfilm p-ZnTe/n-CdTe heterojunctions have been studied in the temperature range of 280-400 K. The p-n junctions were grown by MBE on (100) semi-insulating GaAs substrates. From the analysis of I-V and C-V curves the potential barrier height of the junctions and its temperature dependence are determined. The relatively large value of the temperature coefficient of the potential barrier height (2.5-3.0 × 10^{-3} eV/K) indicates a high density of defects at the p-ZnTe/n-CdTe interface. The presence of interface defects limits the efficiency of the solar energy conversion of these devices.
6
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Graded Quantum Well Structures Made of Diluted Magnetic Semiconductors

81%
Wojtowicz T., Kutrowski M., Karczewski G., Kossut J.
Acta Physica Polonica A
|
1998
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vol. 94
|
issue 2
199-217
EN
In this paper we review results of studies of two types of spatially graded quantum well structures containing various layers of diluted magnetic semiconductors Cd_{1-x}Mn_{x}Te or Cd_{1-x-y}Mn_{x}Mg_{y}Te. The design of the structures has been recently proposed by us and suitable samples have been grown by a modified molecular beam epitaxy method. In the structures of the first type a digital profiling of the composition of the constituent material in the growth direction allowed to produce quantum wells with a specifically required shape of the confining potential (including parabolic, half-parabolic, triangular, and trapezoidal). Such samples were used for (i) determination of the conduction and valence band offsets in MnTe/CdTe and MgTe/CdTe systems, (ii) for the demonstration of an enhanced exciton binding in a parabolic confining potential as well as for (iii) demonstration of the possibility of "spin-splitting engineering" in diluted magnetic semiconductors quantum structures. In the second type of the structures, a precise in-plane profiling of either quantum well width or the barrier width or n-type doping intensity was realized. These structures were subsequently used for studies of the evolution of optical spectra with an increase in the concentration of confined two-dimensional gas of conduction electrons.
7
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Ferroelectric Field Effect Transistor Based on Modulation Doped CdTe/CdMgTe Quantum Wells

81%
Kolkovsky V., Wojciechowski T., Wojtowicz T., Karczewski G.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1173-1178
EN
In this work, we observed effects of changing the electron concentration and electron mobility upon the poling of the Cd_{0.96}Zn_{0.04}Te ferroelectric gate deposited on the top of the CdTe-based modulation doped quantum well structure, which are confirmation of the existence of the electrostatic field originating from the ferroelectric material, which can be controlled by an external voltage. The analysis of the data obtained from the Hall effect measurements showed that the electron mobility and carrier concentration decreased by a factor of 2.5 and 1.5, respectively upon the negative poling of the gate with respect to the poled by the positive voltage. Moreover, the electrostatic field, depending on its directions, causes depletion of accumulation of electrons in the 2D channel, i.e., it is a source of the field effect.
8
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δ-Doped CdTe/Cd_{1-x}Mn_{x}Te Multiple Quantum Wells Investigated by Photoreflectance Spectroscopy

72%
Sitarek P., Misiewicz J., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 5
901-904
EN
Room temperature photoreflectance spectroscopy was used to investigate CdTe/Cd_{1-x}Mn_{x}Te multiple quantum wells grown by MBE. Structures were indium δ-doped into the well or into the barrier. The value of heavy and light hole subbands splitting was measured and compared to the calculated ones. The influence of the position of δ-doping on the measured spectra was shown.
9
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Epitaxial Growths of II-VI Compounds on (110) Substrates

72%
Cywiński G., Wojtowicz T., Kopalko K., Karczewski G., Kossut J.
Acta Physica Polonica A
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1998
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vol. 94
|
issue 2
281-284
EN
We studied epitaxial growth conditions of II-VI semiconductors on (110) substrates, which is indispensable for fabrication of T-shaped quantum wire structures. We experimented with different types of (110)-oriented substrates and monitored the surface quality of deposited layers in situ by reflection high energy electron diffraction and ex situ by photoluminescence. The aim of this work is to find optimum growth conditions of II-VI compounds on a cleaved edge of a superlattice as required by the overgrowth method.
10
Content available remote

Search for T-Shaped Quantum Wires in CdTe/CdMg(Mn)Te System

72%
Cywiński G., Wojtowicz T., Karczewski G., Kossut J., Gębicki W.
Acta Physica Polonica A
|
1998
|
vol. 94
|
issue 2
277-280
EN
We attempted to produce and to investigate T-shaped wire structures of II-VI compounds. Our samples were grown on GaAs hybrid substrates in a two-stage growth process. The photoluminescence measurements resulted into two different possible polarization behaviors of recorder signal. We interpret one of these behaviors as due to quantum wire formation.
11
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Photoluminescence of CdTe/CdMgTe Double Quantum Wells with a Two-Dimensional Electron Gas

72%
Deresz M., Wiater M., Karczewski G., Wojtowicz T., Łusakowski J.
Acta Physica Polonica A
|
2017
|
vol. 132
|
issue 2
390-392
EN
Magnetophotoluminescence measurements at liquid helium temperatures were carried out on asymmetric double quantum wells based on CdTe/CdMgTe heterostructures. Due to doping with shallow iodine donors, a two-dimensional electron gas was present in the quantum wells. The samples studied differed with the quantum well widths and doping level. We show a resemblance of the luminescence to results obtained on single quantum wells which suggests that in samples studied the quantum wells are not strongly coupled.
12
Publication available in full text mode
Content available

Time-Resolved Studies of Excitonic Dynamics in a Wide II-VI Quantum Well by a Femtosecond Pump-Probe Reflectivity

72%
Trajnerowicz A., Golnik A., Kossacki P., Pacuski W., Wojtowicz T.
Acta Physica Polonica A
|
2006
|
vol. 110
|
issue 3
395-401
EN
We present time-dependent reflectance spectra of wide (Cd,Mn)Te/(Cd,Mg)Te quantum wells. Interactions between excitons, trions, and carriers are studied for exciton densities up to 10^{11} cm^{-2}. The resonant excitation at different excitonic lines is analyzed.
13
Publication available in full text mode
Content available

Rare Earth Ion Implantation in GaN: Damage Formation and Recovery

72%
Gloux F., Ruterana P., Wojtowicz T., Lorenz K., Alves E.
Acta Physica Polonica A
|
2006
|
vol. 110
|
issue 2
125-137
EN
Rare earth ions implanted GaN has been investigated by transmission electron microscopy versus the fluence, using Er, Eu or Tm ions at 150 keV or 300 keV and at room temperature. Point defect clusters and stacking faults are generated from low fluences (7×10^{13} at/cm^2), their density increases with the fluence up to the formation of a highly disordered layer at the surface. This highly disordered layer is observed from a threshold fluence of 3×10^{14} at/cm^2 at 150 keV and 3×10^{15} at/cm^2 at 300 keV, and appears to be composed of voids and misoriented nanocrystallites. Its thickness rapidly increases with the fluence, and then saturates. Both basal and prismatic stacking faults were observed. Basal stacking faults are I_1 in majority, but E or I_2 have also been identified. I_1 basal stacking faults propagate easily through GaN by folding from basal to prismatic planes. Channelling implantation, increasing the implantation temperature from room temperature to 500ºC, or implanting through a 10 nm thick AlN cap reduce the crystallographic damage, particularly by retarding the formation of the highly disordered layer. Implanting through the AlN cap allows the highly disordered layer formation threshold fluence to be increased by one order of magnitude, as well as the annealing at high temperature (1300ºC) which brings about a strong optical activation of the rare earths.
14
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Deep Electron Traps in CdTe:In Films Grown by Molecular Beam Epitaxy

72%
Żakrzewski A., Dobaczewski L., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 88
|
issue 5
961-964
EN
N-type indium doped CdTe grown on n^{+}-GaAs by molecular beam epitaxy has been studied by the standard deep level transient spectroscopy and the isothermal Laplace-transform deep level transient spectroscopy. It was found that the Cd/Te flux ratio strongly influences the deep level transient spectroscopy results. The unusual temperature dependence of the electron emission rate in films grown at nearly stoichiometric conditions may point out that the observed defect is resonant with the conduction band.
15
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Strain Relaxation of ZnTe/CdTe and CdTe/ZnTe heterostructures: In Situ Study

72%
Riesz F., Kret S., Karczewski G., Wojtowicz T., Kossut J.
Acta Physica Polonica A
|
1996
|
vol. 90
|
issue 5
911-914
EN
The strain relaxation kinetics of ZnTe/CdTe and CdTe/ZnTe heterostructures grown on GaAs substrates by molecular beam epitaxy are studied by in situ reflection high-energy electron diffraction. The observed critical layer thickness is 5 monolayers for ZnTe/CdTe and less than 1 monolayer for CdTe/ZnTe. The relaxation is anisotropic. Dislocation core parameters and relaxation rate constants were determined using a kinetic model and assuming strain-dependent activation energy of dislocation movement.
16
Content available remote

Light-Controlled Transport in Doped Diluted Magnetic Semiconductors near Localization Boundary

72%
Głód P., Dietl T., Wojtowicz T., Sawicki M., Miotkowski I.
Acta Physica Polonica A
|
1993
|
vol. 84
|
issue 4
657-660
EN
We report milikelvin studies of light induced metastable changes of the conductivity of the In doped Cd_{0.95}Mn_{0.05}Te_{0.97}Se_{0.03} crystals in the vicinity of the metal-insulator transition.
17
Content available remote

Optical Characterization of MBE-Grown Cd_{1-x}Mn_{x}Te Layers by Raman Spectroscopy

62%
Szuszkiewicz W., Dynowska E., Janik E., Karczewski G., Wojtowicz T., Kossut J., Jouanne M.
Acta Physica Polonica A
|
1996
|
vol. 89
|
issue 3
335-340
EN
In this paper we discuss a possibility of an optical characterization of thin semiconductor epilayers by Raman scattering measurements. As an example zinc blende Cd_{1-x}Mn_{x}Te epilayers (0.66 ≤ x ≤ 1.0) have been grown by molecular beam epitaxy method and investigated by Raman scattering and X-ray diffraction. Information resulting from both methods is compared and discussed.
18
Content available remote

Cold and Hot Excitons in CdMnTe/CdMgTe Quantum Wells in Strong Excitation Regime and External Magnetic Field

62%
Trajnerowicz A., Golnik A., Kossacki P., Bardyszewski W., Wiater M., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
|
2009
|
vol. 116
|
issue 5
849-851
EN
Systematic studies of neutral heavy-hole excitonic line energy changes in a strong excitation regime were carried out by means of a pump-probe method for quantum wells containing a 2D gas of free holes. Energy shift of X_{e1hh1} line was analyzed for different excitation energies at fixed delay between pump and probe pulses, also under external magnetic field. It was observed that this shift depends not only on the density of created excitons but also directly on the pump energy. In co-polarization configuration for excitation energy below an absorption resonance the energetic blue shift rises linearly with the elevated exciton density (localized excitons are created). For energies slightly above the resonance, the blue shift diminishes dramatically in spite of high exciton density present (delocalized excitons are created). Model absorption calculations are in qualitative agreement with the experimental data.
19
Content available remote

Non-Ohmic Conductivity of High Resistivity CdTe

62%
Łusakowski J., Szczytkowski J., Szadkowski K., Kamińska E., Piotrowska A., Karczewski G., Wojtowicz T.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 4
803-806
EN
Conductivity measurements were carried out at room temperature on samples of nominally undoped Bridgman, bulk crystals and MBE-grown lay­ers of CdTe. The samples were equipped with indium contacts which made it possible to determine the voltage distribution along the path of the cur­rent flow. The results show that for both types of CdTe almost all of the applied voltage drops in the vicinity of the positively biased contact. The resistance of the samples was shown not to depend on the distance between the pads. The results agree with predictions of model of current injection into semiconductors with deep traps.
20
Content available remote

Exciton Magnetic Polaron Features in Photoluminescence Excitation Spectra of CdTe/(CdMn)Te Quantum Wells with High Mn Contents

62%
Mackh G., Ossau W., Yakovlev D. R., Landwehr G., Wojtowicz T., Karczewski G., Kossut J.
Acta Physica Polonica A
|
1995
|
vol. 88
|
issue 5
849-852
EN
Exciton magnetic polarons are studied in CdTe/Cd_{1-x}Mn_{x}Te (0.4 ≤ x ≤ 0.8) quantum wells. The magnetic polaron formation leads to the appearance of an additional line in the photoluminescence excitation spectra, which can be employed to determine the Zeeman splittings more exactly than by using the free exciton peak. We find an overall increase in the polaron energy with increasing x in the whole range of Mn contents studied.
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