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1
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Transport in Quantum Structures of Diluted Magnetic Semiconductors

100%
Jaroszyński J.
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vol. 96
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issue 5
641-650
EN
This paper reviews recent millikelvin studies of magnetoconductance and noise in nanostructures of a diluted magnetic semiconductor n-Cd_{1-x}Mn_{x}Te. These studies were particularly rewarding for probing the influence of magnetic ions upon mesoscopic phenomena. The accumulated results demonstrated the existence of a new driving mechanism of the universal conductance fluctuations in magnetic systems. Several signatures of spin-glass freezing were observed, such as the appearance of 1/f conductance noise, aging, thermal, and magnetic irreversibilities as well as a strong increase in the amplitude of both conductance fluctuations and noise when temperature and the magnetic field were lowered below the freezing line. A statistical analysis of conductance noise made it possible to investigate the nature of excitations in spin-glass phase, and to discriminate between competing theoretical models.
2
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Metal-Insulator Transition in Doped Semiconductors

100%
Jaroszyński J.
Acta Physica Polonica A
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1991
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vol. 80
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issue 2
255-265
EN
A survey is given of different kinds of metal-insulator transitions (MIT) in doped semiconductors. The role of electron-electron Coulomb interactions and of disorder is discussed vis-a-vis millikelvin experimental results for semimagnetic semiconductors (SMSC) in the vicinity of MIT. Critical behavior of conductivity tensor components and dielectric susceptibility at the magnetic field-induced MIT in p-type Hg_{1-x}Mn_{x}Te is compatible with the model in which the MIT is a result of quantum localization driven by disorder-modified electron-electron interactions. At the same time the critical behavior of the Hall coefficient suggests that, in addition to electrons forming the Fermi liquid (FL) and undergoing localization at the MIT, there is certain a concentration of local electron moments, even on the metallic side of the MIT. The formation of these moments can presumably be described in terms of a disordered Hubbard-Mott model.
3
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High Mobility 2D Electron Gas in CdTe/CdMgTe Heterostructures

39%
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.
4
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Growth and Electrical Properties of Phosphorus Doped Zn_{1-x}Mn_{x}Te Crystals

39%
Khoi L. V., Jaroszyński J., Witkowska B., Mycielski A., Gałązka R. R., Cisowski J.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
833-836
EN
The high pressure Bridgman technique was used to grow Zn_{1-x}Mn_{x}Te:P crystals. Under the N_{2} pressure of 30 atm., we obtained the p^{+}-Zn_{1-x}Mn_{x}Te single crystals 8-10 mm in diameter, with free-carrier densities as high as p ≈ 8×10^{18} cm^{-3} and the room temperature conductivity σ(RT) ≈ 30 Ω^{-1}cm^{-1}. Magnetoresistance measurements were carried out down to 1.3 K and up to 6 T. In Zn_{1-x}Mn_{x}Te:P a strong increase in the acceptor binding energy as well as an immense (ρ(0,1.3K)/ρ(6T,1.3K) > 10^{3}) negative magnetoresistance are observed, by contrast, not seen in diamagnetic ZnTe:P. It is shown that these effects come from the formation of bound magnetic polarons and their destruction by an external magnetic field.
5
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Magnetization Steps in Cd_{1-x}Mn_{x}Te Observed in Coherent Transport

33%
Jaroszyński J., Dietl T., Wróbel J., Karczewski G., Wojtowicz T., Kossut J., Maude D. K., van der Linden P., Portal J. C.
Acta Physica Polonica A
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1997
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vol. 92
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issue 4
797-800
EN
Magnetoconductance measurements on submicron wires of n^{+}-Cd_{1-x}Mn_{x}Te were carried out up to 27 T and down to 100 mK. The inverse correlation field of the universal conductance fluctuations is found to increase abruptly in the vicinity of the magnetization steps due to Mn pairs in CdMnTe. No such effect is observed in similar wires of CdTe. These findings support a recent model, according to which the correlation field of the universal conductance fluctuations in magnetic systems is inversely proportional to the magnetic susceptibility of the localized spins.
6
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Electron Localization in Sb-Doped Si/SiGe Superlattices

33%
Dietl T., Jaroszyński J., Sawicki M., Głód P., Wróbel J., Stöger G., Brunthaler G., Bauer G., Schäffler F.
Acta Physica Polonica A
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1995
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vol. 88
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issue 4
699-702
EN
Millikelvin studies of in-plane magnetoconductance in short period Si/Ge:Sb superlattices have been carried out in order to examine the effect of anisotropy on quantum localization. The field-induced metal-to-insulator transition has been observed, indicating the existence of extended states. This suggests that despite anisotropy as large as D_{∥}/D_{⊥} ≈ 10^{3} the system behaves as 3D in respect of localization by disorder.
7
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Indium Doping of CdTe Grown by Molecular Beam Epitaxy

33%
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.
8
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Content available

Quantum Hall Ferromagnet in Magnetically-Doped Quantum Wells

33%
Andrearczyk T., Jaroszyński J., Wróbel J., Karczewski G., Wojtowicz T., Papis E., Kamińska E., Piotrowska A., Popović D., Dietl T.
Acta Physica Polonica A
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2003
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vol. 104
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issue 2
93-102
EN
The article reviews our recent studies on quantum Hall ferromagnetism in diluted magnetic semiconductors. We carried out magnetoresistance studies on modulation-doped, gated heterostructures of (Cd,Mn)Te/(Cd,Mg)Te:I. We put into evidence the formation of Ising quantum Hall ferromagnet with Curie temperature T_C as high as 2 K. Quantum Hall ferromagnetism is manifested by anomalous magnetoresistance maxima. Moreover, magnitude of these spikes depends dramatically on the history of the sample, shows hysteresis when either magnetic field or gate voltage are swept, stretched-exponential time evolution characteristic of glassy systems, and strong Barkhausen noise. Our study suggests that these metastabilities stem from the slow dynamics of ferromagnetic domains.
9
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Conductance Fluctuations in Microstructures of HgCdMnTe Bicrystals

33%
Grabecki G., Lenard A., Plesiewicz W., Jaroszyński J., Cieplak M., Skośkiewicz T., Dietl T., Kamińska E., Piotrowska A., Bulka B.
Acta Physica Polonica A
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1991
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vol. 80
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issue 2
307-310
EN
Microscopic four-contact probes to semimagnetic HgCdMnTe grain-boundary inversion layers have been photolithographically patterned. Magnetoresistance measurements performed on these samples revealed aperiodic conductance fluctuations of the magnitude of the order of e^{2}/h. Quantitative analysis of both fluctuation amplitude and their mean period indicate that we have approached the mesoscopic regime in our system. This opens new possibilities in studies of spin-subsystem dynamics in semimagnetic semiconductors.
10
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Dimensional Crossovers in Magnetoresistance of Submicron Films and Wires of CdTe:In

27%
Jaroszyński J., Wróbel J., Sawicki M., Skośkiewicz T., Karczewski G., Wojtowicz T., Kossut J., Dietl T., Kamińska E., Papis E., Piotrowska A., Duś R., Nowakowski R.
Acta Physica Polonica A
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1996
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vol. 90
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issue 5
1027-1031
EN
We present millikelvin studies of magnetoresistance for epitaxial films and wires of CdTe:In. In comparison to the data with theoretical predictions for the weakly localized regime we put into the evidence the presence of the temperature-induced dimensional crossovers in the studied systems. Our measurements probe the electron phase-breaking rate and indicate that the main dephasing mechanism arises from electron scattering from thermal fluctuations of three- or two-dimensional electron liquid.
11
Content available remote

Electrical and Structural Properties of Ohmic Contacts to n-Type and High Resistivity CdTe

27%
Kamińska E., Piotrowska A., Guziewicz M., Gierlotka S., Papis E., Łusakowski J., Szadkowski K., Kwiatkowski S., Dietl T., Grabecki G., Jaroszyński J., Karczewski G., Zakrzewski A. K.
Acta Physica Polonica A
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1995
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vol. 87
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issue 2
411-414
EN
The interaction between CdTe and In during the formation of an ohmic contact has been investigated. Emphasis is placed on the study of the effect of thermally induced sublimation of cadmium on electrical properties of con­tacts. Presented results prove the effectiveness of cap annealing and rapid thermal processing in fabrication of improved ohmic contacts with limited Cd losses during the contacting procedure.
12
Content available remote

Conductance Fluctuations in Quantum Wires of n-CdTe and n-Cd_{1-x}Mn_{x}Te

27%
Jaroszyński J., Wróbel J., Sawicki M., Skośkiewicz T., Karczewski G., Wojtowicz T., Kossut J., Dietl T., Kamińska E., Papis E., Barcz A., Piotrowska A.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
1000-1004
EN
We present millikelvin studies of magnetoconductance in submicron wires of In-doped n^{+}-CdTe and n^{+}-Cd_{0.99}Mn_{0.01}Te epilayers. Weak-field magnetoresistance which arises from quantum localization as well as universal conductance fluctuations have been observed. The exchange coupling to magnetic impurities is shown to decrease the correlation field of the fluctuations. This novel effect is interpreted by invoking a new driving mechanism of the magnetoconductance fluctuations - the redistribution of the electrons between energy levels of the system, induced by the giant s-d spin-splitting of the electronic states.
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