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  1. 95 Acta Physica Polonica A

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  1. 95 Karczewski G.

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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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Optical Studies of HgCdMnTe Bicrystals

81%
Grabecki G., Wróbel J., Karczewski G.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
221-223
EN
We report preliminary results of optical measurements performed on Hg_{1-x-k}Cd_{x}Mn_{k}Te grain boundaries. Photovoltaic spectra and I-V characteristics under illumination exhibit metastable behavior, confirming our previous conclusions based on transport measurements under high hydrostatic pressure.
3
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Ultra-Fast Spin Dynamics in Diluted Magnetic Semiconductors

81%
Wilamowski Z., Buczko R., Karczewski G., Jantsch W.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
969-972
EN
In nano-size antiferromagnetic systems a spatially inhomogeneous field leads to the formation of a staggered magnetization. Thereby the total magnetic moment does not change but the formation of a net magnetic moment at the border of the cluster leads to an energy gain. This type of magnetism is characterised by an ultra-fast dynamics. We suggest it is also responsible for the formation of the exciton magnetic polaron.
4
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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.
5
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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.
6
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Weakly Diluted Magnetic CdTe/Cd_{1-x}Mn_{x}Te Semiconductor Structures Grown by MBE

81%
Wojtowicz Τ., Karczewski G., Kossut J.
Acta Physica Polonica A
|
1995
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vol. 88
|
issue 4
631-642
EN
In this paper we review the results of our effort to grow layers and low-dimensional structures containing Cd_{1-x}Μn_{x}Te diluted magnetic semi­conductor with relatively high values of Mn molar fraction x. A high quality of the structures grown so far is demonstrated by making use of results of several selected experiments. In the case of the epilayers having bulk-like thickness with x ≥ 0.7 we discuss, in particular, the magnetic phase dia­gram as well as we report on collective spin excitation (magnons) observed in Raman scattering experiments. The discussion of the growth of different quantum wells, including rectangular, digital, parabolic and wedge quantum wells, is accompanied by a brief overview of their optical and magnetoop­tical properties. These results include first measurements concerning mag­netic polarons in quantum wells embedded in Cd_{1-x}Mn_{x}Te barriers with 0.4 ≤ x ≤ 0.8. Finally, we report on the present status of the search for dimensional effects in the spin-glass phase performed with the use of our specially designed superlattice structures.
7
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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
|
2012
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vol. 122
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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.
8
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Spin Relaxation Processes in Quantum Well Structures of Cd_{1-x}Mn_xTe/Cd_{1-x}Mg_xTe

81%
Khachapuridze A., Ivanov V., Godlewski M., Karczewski G.
|
|
issue 4-5
643-648
EN
Fast spin relaxation of Mn^{2+} ions in a magnetic quantum well of CdMnTe with 1% Mn fraction is related to a very efficient spin-flip interaction between Mn ions and free carriers. This mechanism of spin relaxation becomes dominant at increased excitation densities. The observed response of the photoluminescence bands to the Mn^{2+} magnetic resonance indicates that free carriers are heated at the magnetic resonance conditions. A decrease in formation/recombination rates of free and trion excitons is observed. Donor bound exciton photoluminescence is enhanced, which we relate to delocalization of free excitons, caused by interaction with microwave heated free carriers.
9
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Two Charge States of Sulphur in GaSb

81%
Dobaczewski L., Kaczor P., Karczewski G., Poole I.
Acta Physica Polonica A
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1991
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vol. 79
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issue 1
133-136
EN
Results of the isothermal DLTS, photoconductivity, and photo-Hall measurements, showed that the sulphur-related center in GaSb, being a DX-type defect, has two charge states.
10
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Temperature and Composition Dependence of Photovoltaic Spectra of Pb_{1-x}Mn_{x}Se Diodes

81%
Le-Van-Khoi, Szczerbakow A., Karczewski G., Gałązka R. R.
Acta Physica Polonica A
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1991
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vol. 79
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issue 2-3
287-290
EN
Photovoltaic spectra of Pb_{1-x}Mn_{x}Se homojunctions have been measured in the infrared spectral region within the temperature range 15-300 K. The junctions have been formed by cadmium diffusion into the p-type Pb_{1-x}Mn_{x}Se crystals with manganese content 0 ≤ x ≤ 0.08. From the positions of the photovoltaic maxima the energy band gap of the diode material has been determined. A phenomenological expression describing the energy band gap of Pb_{1-x}Mn_{x}Se as a function of temperature and crystal composition has been proposed. In diodes containing high manganese content x = 0.06 and x = 0.08 a second photovoltaic maximum caused by indirect optical transitions between the main conduction band and the secondary valence band located along the ∑-axis of the Brillouin zone has been observed.
11
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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.
12
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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
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1998
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vol. 94
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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.
13
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Content available

Single Particle and Collective Spin Excitations in Semimagnetic Quantum Wells

81%
Perez F., Jusserand B., Richards D., Karczewski G.
Acta Physica Polonica A
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2004
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vol. 106
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issue 3
311-317
EN
Collective and single-particle spin-flip excitations of a two-dimensional electron gas in a semimagnetic Cd_{1-x}Mn_xTe quantum well are observed by resonant Raman scattering. Application of a magnetic field splits the spin-subbands and a spin-polarization is induced in the electron gas. Above some critical field, a collective spin-flip mode, which disperses with in-plane wave vector, dominates the spectra. The energy of this mode is given by the bare Zeeman energy at vanishing wave vector as predicted by Larmor's theorem and its in-plane dispersion is well described by a model of the interacting polarizability of a spin polarized electron gas when both exchange and correlation are taken into account.
14
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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.
15
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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.
16
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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
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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.
17
Content available remote

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
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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.
18
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High-Resolution X-Ray Diffraction Studies on MBE-Grown p-ZnTe/n-CdTe Heterojunctions for Solar Cell Applications

72%
Wichrowska K., Domagala J., Wosinski T., Chusnutdinow S., Karczewski G.
|
|
vol. 126
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issue 5
1083-1086
EN
High-resolution X-ray diffractometer was used to study structural quality, lattice parameters and misfit strain in p-ZnTe/n-CdTe heterojunctions grown by the molecular-beam epitaxy technique on two different (001)-oriented substrates of GaAs and CdTe. The X-ray diffractometer results indicate that the CdTe layers, grown on lattice mismatched GaAs substrate, are partially relaxed, by the formation of misfit dislocations at the interface, and display residual vertical strain of the order of 10^{-4}. The presence of threading dislocations in the layers effectively limits the efficiency of solar energy conversion in the investigated heterojunctions. Homoepitaxially grown CdTe layers, of much better structural quality, display unexpected compressive strain in the layers and the relaxed lattice parameter larger than that of the substrate. Possible reasons for the formation of that unusual strain are discussed.
19
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Magnetooptical Properties of Pb_{1-x}Mn_{x}Se p-n Junctions

72%
Khoi L., Karczewski G., Dobrowolski W., Kossut J., Gałązka R.
Acta Physica Polonica A
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1991
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vol. 80
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issue 3
445-448
EN
The first experimental evidence of the magnetic quantum oscillation in the photovoltaic effect of Pb_{1-x}Mn_{x}Se p-n junctions is reported. The p-n junctions were obtained in Pb_{1-x}MnxSe crystals with manganese content, 0 ≤ x ≤ 0.08 by introducing Cd donors by diffusion. Measurements were per formed between 5-85 K and in the presence of the magnetic field 0-7 T in the Faraday and Voigt configurations of the incident infrared radiation of various photon energies in the vicinity of the energy gap of a Pb_{1-x}Mn_{x}Se. Strong oscillatory behavior of the photovoltage was observed as a function of the magnetic field intensity at a constant wavelength of the incident light. Using the model of Adler of the energy band structure modified by the exchange terms, and after identification of the initial and final states of the transitions, we derive the band parameters of the Pb_{1-x}Mn_{x}Se crystals.
20
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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
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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.
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