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1
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Development of CdTe/Cd_{1-x}Mg_{x}Te Double Barrier, Single Quantum Well Heterostructures for Resonant Tunneling

100%
Reuscher G., Keim M., Fischer F., Waag A., Landwehr G.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
885-888
EN
We report the first observation of resonant tunneling through a CdTe/Cd_{1-x}Mg_{x}Te double barrier, single quantum well heterostructure. Negative differential resistance is observable at temperatures below 230 K, exhibiting a peak to valley ratio of 3:1 at 4.2 K.
2
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Optically Detected SdH Oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te Modulation Doped Quantum Wells

100%
Shen J. X., Ossau W., Fischer F., Waag A., Landwehr G.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
1033-1037
EN
Oscillations of photoluminescence properties in external magnetic fields are investigated in CdTe modulation doped quantum wells. The oscillatory behaviour of the luminescence intensity, the line width and the g factor is due to many-body effects in the 2-dimensional electron gas. The oscillation of photoluminescence intensity can be easily used as optically detected Shubnikov de Haas effect to determine the electron concentration in quantum wells without contacts.
3
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Effect of Magnetic Polaron Formation on the Exciton Mobility Edge in Cd_{1-x}Mn_{x}Te

100%
Mackh G., Yakovlev D., Ossau W., Waag A., Landwehr G.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
265-268
EN
We study the exciton localization in the semimagnetic semiconductor Cd_{1-x}Mn_{x}Te by selective excitation of the exciton photoluminescence. We show that the energy position of the effective mobility edge for excitons is subject to the competition between nonmagnetic and magnetic localization due to the magnetic polaron formation. External magnetic fields affect this competition by suppressing the polaron formation, which shifts the mobility edge.
4
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Characterization of Interfaces in Semimagnetic Quantum Wells

86%
Schmitt G., Kuhn-Heinrich B., Zehnder U., Ossau W., Litz T., Waag A., Landwehr G.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
897-900
EN
The interfaces between nonmagnetic CdTe quantum wells and semimagnetic barriers of Cd_{1-x}Mn_{x}Te were investigated for several well widths by low temperature photoluminescence and photoluminescence excitation spectroscopy. Specially designed Cd_{1-x}Mn_{x}Te/CdTe/Cd_{1-y}Mg_{y}Te structures enable us to distinguish the quality of the semimagnetic normal and inverted interfaces. The normal interface shows to have a better structural quality than the inverted interface.
5
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Dimensional Dependence of Exchange Interactions at High Magnetic Fields

86%
Zehnder U., Kuhn-Heinrich B., Ossau W., Waag A., Landwehr G., Cheng H., Nicholas R.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
989-992
EN
We studied the contribution of the breaking of antiferromagnetically coupled spin clusters to the total magnetization in thin (CdMn)Te layers as a function of the layer thickness by reflectivity spectroscopy in magnetic fields up to 45 T. The experimental results show that the contribution of the breaking of antiferromagnetically coupled spin clusters is reduced by decreasing layer thickness.
6
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Exciton Magnetic Polaron Features in Photoluminescence Excitation Spectra of CdTe/(CdMn)Te Quantum Wells with High Mn Contents

86%
Mackh G., Ossau W., Yakovlev D. R., Landwehr G., Wojtowicz T., Karczewski G., Kossut J.
Acta Physica Polonica A
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1995
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vol. 88
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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.
7
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Doping of the Wide-Gap Semiconductor Cd_{1-x}Mg_{x}Te During Molecular Beam Epitaxy

86%
Fischer F., Litz T., Waag A., Heinke H., Scholl S., Gerschütz J., Landwehr G.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
487-491
EN
We investigated the n-type doping of the wide-gap II-VI semiconductor (CdMg)Te. The n-type doping of (CdMg)Te has previously been achieved in only a small range of magnesium concentration. By the use of zinc iodine as dopant source material, we obtained highly doped (CdMg)Te layers up to a magnesium concentration of 40%. The limiting factor for the free carrier concentration at room temperature is the occurrence of a deep level, which dominates the electrical properties at room temperature of layers with more than 30% magnesium. Compensating defects or defect complexes are con­sidered, to explain the observed properties of the deep level, which do not seem to be characteristic of an isolated donor state.
8
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Optical Anisotropy of ZnSe/BeTe Superlattices Probed by Excitonic Spectroscopy

73%
Platonov A., Kochereshko V., Ivchenko E., Yakovlev D., Ossau W., Fischer F., Waag A., Landwehr G.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
479-482
EN
Photoluminescence spectra of type-II ZnSe/BeTe superlattices were studied. A linear polarised photoluminescence has been found in the spectral range of spatially indirect exciton transitions. This observation is interpreted in a model of optical anisotropy of heterostructures with no-common atom at interfaces.
9
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Investigation of Spin-Glass Transition in Semimagnetic Quantum Wells Based on Cd_{1-x}Mn_{x}Te by Means of Optical Spectroscopy

73%
Zehnder U., Yakovlev D. R., Ossau W., Waag A., Landwehr G., Wojtowicz T., Karczewski G., Kossut J.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
1075-1078
EN
The spin-glass transition in Cd_{1-x}Mn_{x}Te epitaxial layers and bulk samples with 0.24 ≤ x ≤ 0.43 and in quantum well structures on the basis of Cd_{1-x}Mn_{x}Te were investigated by means of optical spectroscopy. Reduction of dimensionality of Cd_{1-x}Mn_{x}Te layers down to the quasi-two-dimensional case realized in Cd_{1-x}Mn_{x}Te/Cd_{1- y}Mn_{y}Te heterostructures frustrates the spin-glass formation, which is in agreement with theoretical predictions. The spin-glass formation is also frustrated in the vicinity of interfaces between semimagnetic and nonmagnetic semiconductors in CdTe/Cd_{1-x}Mn_{x}Te quantum wells.
10
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Exciton States in Type-II ZnSe/BeTe Quantum Wells

73%
Platonov A. V., Yakovlev D. R., Zehnder U., Kochereshko V. P., Ossau W., Fischer F., Litz T., Waag A., Landwehr G.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
953-957
EN
We present an optical investigation of novel heterostructures based on beryllium chalcogenides with a type-I and type-II band alignment. In the type-II quantum well structures (ZnSe/BeTe) we observed a strong exciton transition involving an electron confined in the conduction band well and a hole localized in the valence band barrier (both in ZnSe layer). This transition is drastically broadened by the temperature increase due to enhanced exciton-acoustic phonon interaction.
11
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Model Study of Inhomogeneous Line Broadening in Excitonic Spectra of Quantum Wells

73%
Astakhov G., Kochereshko V., Kosobukin V., Yakovlev D., Wojtowicz T., Karczewski G., Kossut J., Ossau W., Landwehr G.
Acta Physica Polonica A
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1998
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vol. 94
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issue 2
235-239
EN
An approach is proposed to estimate separately parameters of homogeneous and inhomogeneous broadenings from an optical reflection line of a quasi-2D exciton. A phenomenological model is proposed to take into account statistically an inhomogeneous broadening of the exciton resonant spectra. The concept is applied to study a modulation-doped heterostructures with a single quantum well CdTe/CdMgTe. From exciton reflection lines taken in a magnetic field the temperature-dependent homogeneous and inhomogeneous broadening parameters as well as the exciton radiative decay rate are measured.
12
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Investigations on ZnSe/GaAs Interface by Treatment of GaAs (2×4) Surface with Te and Mg

73%
Ebel R., Spahn W., Ress H., Albert D., Schäfer H., Ehinger M., Faschinger W., Landwehr G.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
767-772
EN
The heterovalent interface ZnSe/GaAs, despite the small lattice misfit, still poses certain problems. The condition of the substrate surface prior to growth start determines the initial growth conditions, which on the other hand are assumed to be responsible for defect densities. Since Zn, in contrast to Se, hardly binds to GaAs the initial surface during growth start is essentially Se terminated. Therefore the binding of Mg to Se terminated GaAs was investigated. The structural quality of 140 nm thick ZnSe layers on different MgSe coverages were compared to conventionally grown and Te initiated ZnSe epilayers of the same thickness.
13
Content available remote

Novel CdTe/CdMgTe Graded Quantum Well Structures

73%
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¯).
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