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1
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Graded Quantum Well Structures Made of Diluted Magnetic Semiconductors

100%
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.
2
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High Mobility 2D Electron Gas in CdTe/CdMgTe Heterostructures

76%
Karczewski G., Jaroszyński J., Kutrowski M., Barcz A., Wojtowicz T., Kossut J.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
829-832
EN
We report on iodine doping of molecular beam epitaxy (MBE)-grown Cd(Mn)Te quasi-bulk films and modulation-doped CdTe/Cd_{1-y}Mg_{y}Te two-dimensional (2D) single quantum well structures. Modulation doping with iodine of CdTe/Cd_{1-y}Mg_{y}Te structures resulted in fabrication of a 2D electron gas with mobility exceeding 10^{5} cm^{2}/(V s). This is the highest mobility reported in wide-gap II-VI materials.
3
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Many-Body Interaction Evidenced through Exciton-Trion-Electron Correlated Dynamics

76%
Portella-Oberli M., Berney J., Deveaud B., Ciulin V., Kutrowski M., Wojtowicz T.
Acta Physica Polonica A
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2004
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vol. 106
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issue 3
423-434
EN
Interactions among excitons, trions, and electrons are studied in CdTe modulation-doped quantum wells. These many-body interactions are investigated through the nonlinear dynamical properties in the excitonic complexes using time and spectrally resolved pump and probe techniques. This study is performed as a function of temperature and densities of excitons, trions, and electrons. The results reveal that the nonlinearities induced by trions differ from those induced by excitons and moreover they are mutually correlated. The correlated behavior of excitons and trions manifests itself by crossed trion-exciton effects. We propose that the main source of these correlations is due to the presence of electrons in the quantum well and that its physical origin is the Pauli exclusion-principle. We find that, at 5 K, trions are formed from excitons within 10 ps; at 20 K a thermal equilibrium is reached within 5 ps.
4
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Temperature Study of Photoluminescence from Deep CdTe/Cd_{1-x}Mn_{x}Te Quantum Wells

64%
Kutrowski M., Wojtowicz T., Karczewski G., Kopalko K., Zakrzewski A. K., Janik E., Grasza K., Łusakowska E., Kossut J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
500-504
EN
The photoluminescence studies in CdTe/CdMnTe quantum wells are reported in the temperature range 10-300 K. The MnTe concentration in the barriers is x = 0.3, 0.5, 0.63 and 0.68. Thus the potential wells in our samples are very deep, of the order of ≈ 800 meV in the conduction band and ≈ 200 meV in the valence band in the case of the x = 0.68 sample. In spite of the large lattice mismatch (related to high x value) between the wells and the barriers the observed line widths are as narrow as 2 meV in the case of 100 Å. Clear manifestations of internal strain are observed. In particular, the temperature coefficient of the luminescence energies shows strong dependence on the width of wells.
5
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Cd_{1-x}Mn_{x}Te Parabolic Quantum Wells

64%
Wojtowicz T., Kutrowski M., Cywiński G., Dynowska E., Karczewski G., Kossut J., Fiederling R., Mackh G., Zehnder U., Ossau W.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
977-980
EN
We report on the growth and optical studies of II-VI semiconductor parabolic quantum wells made of Cd_{1-x}Mn_{x}Te for a broad range of quantum well widths and Mn molar fractions x. Photoluminescence excitation spectra revealed several series of peaks equidistant in energy associated with interband optical transitions between harmonic oscillator levels. From the analysis of the spectra the valence band offset Q_{hh} = 0.44±0.1 was determined for the CdTe/Cd_{1-x}Mn_{x}Te system.
6
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Magnetic Characterization of Molecular Beam Epitaxy Grown Cd_{1_{x}}Mn_{x}Te Structures

64%
Sawicki M., Kolesnik S., Wojtowicz T., Karczewski G., Janik E., Kutrowski M., Żakrzewski A., Dynowska E., Dietl T., Kossut J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
169-172
EN
The paper reports on the application of SQUID magnetometry to probe magnetic ion distribution in epilayers and at interfaces of diluted magnetic semiconductors. We present also new results on the possible influence of the magnetic confinement on the formation of the spin-glass phase, and on antiferromagnetic phase transition in zinc-blende MnTe.
7
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Digital Magnetic Quantum Wells for the Study of Interface Sharpness of Molecular Beam Epitaxy Grown Structures

64%
Wojtowicz T., Karczewski G., Żakrzewski A., Kutrowski M., Janik E., Dynowska E., Kopalko K., Kret S., Kossut J., Laval J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
165-168
EN
We report on the growth and basic characterization of digital magnetic quantum wells, that is, quantum wells in which the well material is itself a short period superlattice composed of alternating diluted magnetic and nonmagnetic semiconductor layers each only a few monolayers thick. These novel structures can be useful in a variety of studies, including studies of barrier-well interface sharpness.
8
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Carrier Density Control by Illumination in Surface Doped, p-Type (Cd,Mn)Te Quantum Wells

64%
Maślana W., Kossacki P., Gaj J., Ferrand D., Bertolini M., Tatarenko S., Cibert J., Kutrowski M., Wojtowicz T.
Acta Physica Polonica A
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2006
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vol. 110
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issue 2
255-262
EN
We report both decrease and increase in the 2D carrier gas density in a simple (Cd,Mn)Te/(Cd,Mg)Te heterostructure with (Cd,Mn)Te quantum well. The two effects were achieved by light with different photon energies. The quantum wells were 10 nm wide with 2D hole gas supplied by surface states. For the sample with 25 nm cap layer thickness, it was possible to tune the hole gas concentration from almost empty well (hole density below 1×10^{10} cm^{-2}) to 45×10^{10} cm^{-2}. The illumination with 425 nm wavelength almost doubled the hole gas density from the initial 24×10^{10} cm^{-2}. The depletion mechanism was most effective for illumination with the orange (575 nm) light.
9
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Cubic MnTe - Growth by Molecular Beam Epitaxy and Basic Structural Characterization

64%
Zakrzewski A., Janik E., Dynowska E., Leszczyński M., Kutrowski M., Wojtowicz T., Karczewski G., Bąk-Misiuk J., Domagała J., Kossut J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
433-436
EN
We report on growth by molecular beam epitaxy of thick layers of MnTe with zinc blende structure. Films as thick as 5.6 µm were obtained. Char­acterization by X-ray diffraction proved their good structural quality. We determined the lattice constant and its temperature dependence. Broad lu­minescence due to internal Mn^{2+}- transitions was observed. It showed an unexpected temperature dependence.
10
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(120)-Oriented CdTe/CdMnTe Quantum Well Structures Grown by Molecular Beam Epitaxy

64%
Kutrowski M., Karczewski G., Cywiński G., Surma M., Grasza K., Łusakowska E., Kossut J., Wojtowicz T.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
879-882
EN
We report on the MBE growth and magnetooptical studies of (120)-oriented CdTe/CdMnTe quantum well structures. The quality of structures, as evaluated by the photoluminescence line width, was as good as that of the best structures grown in ⟨100⟩ direction. No spin splitting enhancement, expected theoretically, due to the reduction of the antiferromagnetic interaction between Mn ions in CdTe/CdMnTe digital alloy quantum wells grown along ⟨120⟩ direction was observed.
11
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Novel CdTe/CdMgTe Graded Quantum Well Structures

64%
Wojtowicz T., Kutrowski M., Karczewski G., Cywiński G., Surma M., Kossut J., Yakovlev D. R., Ossau W., Landwehr G., Kochereshko V.
|
EN
We report on growth and magnetooptical studies of two types of novel CdTe/CdMgTe quantum well structures having a precisely controlled grading of either the quantum well width or the donor concentration in a direction perpendicular to the growth axis. The presence of two-dimensional electron gas of varying concentration produced by the graded modulation doping was evidenced by observation of negatively charged exciton-electron complexes (X¯).
12
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Indium Doping of CdTe Grown by Molecular Beam Epitaxy

64%
Karczewski G., Zakrzewski A., Kutrowski M., Jaroszyński J., Dobrowolski W., Grodzicka E., Janik E., Wojtowicz T., Kossut J., Barcz A.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
241-244
EN
We report on n-type indium doping of CdTe films grown by molecular beam epitaxy on (001) GaAs substrates. By adjusting the flux of In atoms we can precisely control the carrier concentration over three orders of magnitude - from 8 × 10^{14} up to 1.3 × 10^{18} cm^{-3}. In agreement with earlier reports we confirmed that Cd overpressure plays an important role in the doping process. The doping appears to be most effective for Cd/Te pressure ratio of 1.5. For this value of Cd/Te pressure ratio essentially 100% efficiency of doping is achieved at low In concentrations (< 10^{18} cm^{-3}). At higher In concentrations acceptor impurities compensate shallow donors limiting the concentration of free carriers.
13
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Luminescence Decay in Deep Quantum Wells CdTe/Cd_{0.5}Mn_{0.5}Te at Room Temperature

64%
Kowalczyk L., Fancey S., Buller G. S., Massa J. S., Kutrowski M., Janik E., Karczewski G., Wojtowicz T., Zakrzewski A. K., Kossut J.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
508-513
EN
Time-resolved photoluminescence was used to study exciton recombi­nation in deep CdTe/Cd_{0.5}Mn_{0.5}Te single quantum well. The width of the investigated well was 100 A. The study was performed at room temperature. The lifetime of the exciton determined in this work has a value comparable to that observed in shallow CdTe/Cd_{0.85}Mn_{0.15}Te quantum wells. A strong enhancement of the photoluminescence decay time with increasing intensity of the exciting laser beam is observed which is indicative of saturation of the non-radiative recombination centers.
14
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Half-Parabolic Quantum Wells of Diluted Magnetic Semiconductor Cd_{1-x}Mn_{x}Te

52%
Kutrowski M., Wojtowicz T., Cywiński G., Karczewski G., Janik E., Dynowska E., Kossut J., Kossacki P., Fiederling R., Pfeuffer-Jeschke A., Ossau W.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
887-890
EN
We report on magnetooptical studies of MBE-grown half-parabolic CdTe/Cd_{x}Mn_{1-x}Te quantum well structures. The value of the valence band offset Q_{v}=0.4 ± 0.05 was determined by comparing energies of optical transitions in the absence of a magnetic field with model calculations. This value was verified by fitting the observed spin splitting of the lowest heavy hole (hh) state. We discuss also the temperature dependence of Q_{v}.
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