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1
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ESR Study of the Magnetic Properties of the CdTe/CdMnTe Multi Quantum Wells

100%
Surma M., Godlewski M., Waag A.
Acta Physica Polonica A
|
1993
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vol. 84
|
issue 3
543-546
EN
The results of electron spin resonance investigations of bulk Cd_{1-x}Mn_{x}Te and of molecular beam epitaxy grown CdTe/CdMnTe single 2 μm thick layer and multi quantum well with Mn concentrations of about x = 0.10 are compared. The Mn^{2+} electron spin resonance spectrum of the MQW CdTe/CdMnTe shows several features different from those observed in the CdMnTe bulk sample. The Mn^{2+} resonance shows a small anisotropy of position and width with the anisotropy axis normal to the heterointerface. The temperature dependence of the width of the electron spin resonance line is also different from that observed for the bulk and for the thick single layer.
2
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Optically Detected SdH Oscillations in CdTe/(CdMg)Te and CdTe/(CdMnMg)Te Modulation Doped Quantum Wells

88%
Shen J. X., Ossau W., Fischer F., Waag A., Landwehr G.
Acta Physica Polonica A
|
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

88%
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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Hydrostatic Pressure Study of MBE CdMnTe Doped with Bromine

88%
Szczytko J., Wasik D., Przybytek J., Baj M., Waag A.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
933-936
EN
We present Hall effect and resistivity measurements as a function of pressure performed on MBE-grown Cd_{1-x}Mn_{x}Te (with x = 0.14) layer (1 μm) doped with bromine. The experimental data were analysed using positive and negative U model of the Br centres. We found that both models could reproduce the experimental points, but in the case of positive U model - only under assumption that the sample was completely uncompensated.
5
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Development of CdTe/Cd_{1-x}Mg_{x}Te Double Barrier, Single Quantum Well Heterostructures for Resonant Tunneling

88%
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.
6
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Optically Detected Cyclotron Resonance Studies of CdMnTe/CdTe Multiquantum Wells and CdMgTe/CdMnTe Superlattices

76%
Godlewski M., Świątek K., Harris C. I., Bergman J. P., Monemar B., Waag A.
Acta Physica Polonica A
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1995
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vol. 87
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issue 1
213-216
EN
The results of photoluminescence, time resolved photoluminescence (de­cay times), optically detected cyclotron and magnetic resonances investiga­tions of CdMnTe/CdTe multiquantum wells and CdMgTe/CdMnTe super-lattices are presented. The role of defects and quantum well width fluctua­tions in recombination processes of 2D carriers is discussed.
7
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Dimensional Dependence of Exchange Interactions at High Magnetic Fields

76%
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.
8
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Optically Pumped Low Threshold ZnSe Based Lasers with 2.8 ML CdSe Active Region

76%
Sorokin S., Toropov A., Shubina T., Lebedev A., Sedova I., Ivanov S., Waag A.
Acta Physica Polonica A
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1998
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vol. 94
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issue 3
539-544
EN
Room-temperature optically pumped (Zn,Mg)(S,Se)/(Zn,Cd)Se laser structures have been grown by molecular beam epitaxy. Using of alternatively-strained short-period superlattice waveguide results in low threshold power density values over the whole blue-green (470-520 nm) wavelength range. Incorporation of CdSe fractional monolayer active region provides more than fourfold further decrease in threshold with respect to quantum well laser structure. Optical and structural properties of laser structure with 2.8 monolayer CdSe are discussed in detail.
9
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Doping of the Wide-Gap Semiconductor Cd_{1-x}Mg_{x}Te During Molecular Beam Epitaxy

76%
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.
10
Content available remote

Characterization of Interfaces in Semimagnetic Quantum Wells

76%
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.
11
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Optical Anisotropy of ZnSe/BeTe Superlattices Probed by Excitonic Spectroscopy

64%
Platonov A., Kochereshko V., Ivchenko E., Yakovlev D., Ossau W., Fischer F., Waag A., Landwehr G.
|
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.
12
Content available remote

Investigation of Spin-Glass Transition in Semimagnetic Quantum Wells Based on Cd_{1-x}Mn_{x}Te by Means of Optical Spectroscopy

64%
Zehnder U., Yakovlev D. R., Ossau W., Waag A., Landwehr G., Wojtowicz T., Karczewski G., Kossut J.
|
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.
13
Content available remote

Exciton States in Type-II ZnSe/BeTe Quantum Wells

64%
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
|
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.
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