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  1. 13 Karczewski G.

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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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Structural and Optical Studies of CdTe/ZnTe Superlattices with Ultrathin ZnTe Layers

100%
Mariette H., Jouneau P., Pelekanos N., Tardot A., Feuilet G., Magnea N.
Acta Physica Polonica A
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1993
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vol. 84
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issue 3
423-433
EN
Spatially selective introduction of ultrathin ZnTe layers (1 to 3 mono-layers) into CdTe allows the study of special superlattice structure, corresponding to a monomolecular plane-host crystal system. Particular attention is given to the strain state control of the inserted ZnTe monolayer. High resolution electron microscopy is used to measure the local lattice distortion: the method yields the location and the total amount of Zn per period, and the results are compared with X-ray diffraction data. Optical properties of these superlattices are also presented. All results show the ability to control ultrathin pseudomorphic layers of ZnTc within CdTe, with limited Zn segregation, and of high crystalline and optical quality. In addition, they can be fitted within the framework of elasticity theory for the structural data, and of a finite quantum well model for the optical ones, even in the ultimate limit of only one nominal ZnTe monolayer.
3
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Optical and Electrical Properties of Highly Doped ZnO:Al Films Deposited by Atomic Layer Deposition on Si Substrates in Visible and Near Infrared Region

100%
Romanyuk V., Dmitruk N., Karpyna V., Lashkarev G., Popovych V., Dranchuk M., Pietruszka R., Godlewski M., Dovbeshko G., Timofeeva I., Kondratenko O., Taborska, M., Ievtushenko A.
Acta Physica Polonica A
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2016
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vol. 129
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issue 1a
A-36-A-40
EN
Optical properties of ZnO films doped by Al in the range 0.5 to 7 at.% and deposited by atomic layer deposition were studied in visible and infrared spectral range. Spectral dependences of film optical permittivity were modeled with the Lorentz-Drude approximation resulting in ZnO:Al plasma frequency and plasma damping parameters. We observed changing electron effective mass from 0.29m₀ to 0.5m₀ with increasing electron concentration in the range (0.9-4) × 10²⁰ due to the phenomenon of conduction band non-parabolicity. Comparing the results of optical and electrical investigations we can see that the main scattering mechanism is the scattering on grain boundaries (its contribution is about 60%).
4
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Content available

Injection of Optically Generated Spins through Magnetic Nonmagnetic Heterointerface: Ruling out Possible Detection Artifacts

100%
Ghali M., Kossut J., Janik E.
Acta Physica Polonica A
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2004
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vol. 106
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issue 2
207-214
EN
We report on injection of optically created spin-polarized carriers into CdTe-based materials. The injected spins are initially aligned in a diluted magnetic semiconductor CdMnTe layer located on the top of CdMgTe layer in CdMnTe/CdMgTe spintronic generic model structures. A critical discussion of possible artifacts that may complicate the spin detection and its quantitative analysis is given. Although the spin injection efficiency, 80%, has been found by us to be basically independent of the thickness of the spin detecting layer, there is an essential difference between thin and wide detectors related to the strain-induced lifting of the valence band degeneracy in the former, when assessing the efficiency of the spin injection. Most importantly, we observe an effect of switching the spin injection process on and off by an external magnetic field variation within a relatively narrow field range. This effect can be achieved by a careful design of the interface between the diluted magnetic semiconductor and the non-magnetic semiconductor.
5
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Hydrostatic Pressure Study of MBE CdMnTe Doped with Bromine

100%
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.
6
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Deep Electron Traps in CdTe:In Films Grown by Molecular Beam Epitaxy

100%
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.
7
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Two-Electron DX State in CdTe:In

100%
Skierbiszewski C., Wiśniewski P., Litwin-Staszewska E., Suski T., Wilamowski Z., Zakrzewski A., 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
927-930
EN
In this paper we investigate electron emission/capture from/to the DX state of indium in CdTe by means of high pressure freeze-out cycle and steady-state photo-conductivity experiments. The results indicate that the DX state is occupied by two electrons. A comparison with deep level transient spectroscopy data shows that two-electron emission occurs at low temperatures, while one-electron emission takes place at high temperatures.
8
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Influence of Interface-Induced Disorder on Classical and Quantum Conductivity of CdTe:IN Epitaxial Layers

100%
Łusakowski J., Karpierz K., Grynberg M., Karczewski G., Wojtowicz T., Contreras S., Callen O.
Acta Physica Polonica A
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1997
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vol. 92
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issue 5
911-914
EN
An influence of disorder originated from the substratelayer interface on electrical properties of CdTe:In layers was investigated by means of the Hall effect and magnetoresistance measurements at low temperatures. An estimation of a scattering rate due to interface-induced disorder is given. Characteristic features of a magnetic field dependence of magnetoresistance are explained by an influence of quantum interference of scattered electron waves both in the hopping and the free electron conductivity regimes.
9
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Indium Doping of CdTe Grown by Molecular Beam Epitaxy

100%
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.
10
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Absorption of Thin ZnSe, ZnS and ZnS_{x}Se_{1-x} Films under High Hydrostatic Pressure

100%
Griebl E., Schőtz G. F., Birzer C., Kerner W., Reisinger T., Hahn B., Gebhardt W.
Acta Physica Polonica A
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1995
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vol. 88
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issue 5
995-999
EN
We present absorption measurements on free-standing ZnSe, ZnS and ZnS_{x}Se_{1-x} films (d = 0.4...2 μm) under hydrostatic pressure up to 15 GPa. The refraction index n(λ,P) of ZnS and ZnSe in the transparent region up to 800 nm and the pressure shift of the E0 absorption edge of ZnSe and some ZnS_{x}Se_{1-x}-compositions was investigated at 293 K. At 2 K free exciton states near the E_{0-} and E_{0} + Δ_{0}-gap are visible in absorption. Increase in the Rydberg energy under pressure was found, which is explained with k • p-theory in the framework of the hydrogen model.
11
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Electron Transport in Submicron Wires of Semiconductors

80%
Wróbel J.
Acta Physica Polonica A
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1996
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vol. 90
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issue 4
691-701
EN
We review the methods of fabrication and transport properties of submicron II-VI, IV-VI and III-V semiconductor wires. Devices were prepared by electron-beam lithography and used for detailed magnetotransport studies, carried out at low (down to 30 mK) temperatures. We discuss a number of novel features obtained in ballistic, diffusive and localized transport regimes. In particular, we describe the universal conductance fluctuations for semimagnetic materials (CdMnTe) and discuss the edge channel transport for PbTe, PbSe and GaAs/GaAlAs systems.
12
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Limitations on Thickness of Absorber Layer in CdS/CdTe Solar Cells

80%
Mykytyuk T., Roshko V., Kosyachenko L., Grushko E.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1073-1076
EN
Calculations of the integrated absorptive capacity of CdTe layer taking into account the spectrum of the AM1.5 solar radiation and the absorption coefficient of CdTe are carried out. The recombination losses at the front and rear surfaces of the CdTe layer and in the space-charge region are also calculated based on the continuity equation. The restrictions on the thickness of CdTe in CdS/CdTe heterojunction have been ascertained taking into account all types of losses. It is shown that in CdTe, the almost complete absorption of photons (99.9%) in the hν > E_{g} range is observed at a layer thickness of more than 20-30 μm, and the absorptive capacity of photons in a CdTe layer of thickness 1 μm is about 93%. The obtained results indicate that when the CdTe absorber layer is very thin, it is impossible to avoid a noticeable decrease of the short circuit current density J_{sc} as compared with a typical thickness of the absorber layer. The loss in J_{sc} is 19-20% when the thickness is 0.5 μm compared to 5% for a thickness of 2-3 μm.
13
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Spectral Distribution of Photoelectric Efficiency οf Thin-Film CdS/CdTe Heterostructure

80%
Kosyachenko L., Lashkarev G., Grushko E., Ievtushenko A., Sklyarchuk V., Mathew X., Paulson P.
Acta Physica Polonica A
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2009
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vol. 116
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issue 5
862-864
EN
The spectral distribution of the quantum efficiency in thin-film CdS/CdTe solar cells is being investigated by taking into account the drift and diffusion components of photocurrent, recombination at the CdS-CdTe interface, the back surface of the CdTe absorber layer and in the space-charge region. The effect of uncompensated acceptor concentration, lifetime of minority carriers and surface recombination velocity on the charge collection efficiency are discussed. The losses caused by reflections and absorption in the CdS and indium tin oxide layers are also considered.
14
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Influence of Magnetic Impurities upon Universal conductance Fluctuations

80%
Dietl T.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
161-171
EN
Mesoscopic phenomena in quantum structures which incorporate magnetic impurities with localized spins may exhibit a number of novel features driven by spin-disorder scattering, exchange spin-splitting of electron bands, and the formation of bound magnetic polarons. After brief information on these effects, their influence on universal conductance fluctuations as well as on low frequency noise and quantum localization is presented. Millikelvin investigations of diffusive charge transport, which have been carried out for submicron wires of n^{+}-Cd_{1-x}Mn_{x}Te epilayers, are reviewed in some details. These studies have provided information on the significance of spin-disorder scattering in semiconductors and put into the evidence 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 exchange spin-splitting. Important implications of these findings for previous interpretations of spin effects in semiconductor and metal nanostructures are discussed.
15
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Magnetization Steps in Cd_{1-x}Mn_{x}Te Observed in Coherent Transport

80%
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.
16
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Preparation and Characterization of Nanocrystalline PbS Thin Films Produced by Chemical Bath Deposition

80%
Göde F., Yavuz F., Kariper İ.
Acta Physica Polonica A
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2015
|
vol. 128
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issue 2B
B-215-B-218
EN
Lead sulfide thin films are deposited on glass substrates at room temperature for 2 h by chemical bath deposition. The structure, surface morphology, optical and electrical properties of the thin films are characterized by X-ray diffraction, scanning electron microscopy, atomic force microscopy, optical absorption spectroscopy and the Hall effect measurements. The obtained films show the formation of well crystallized PbS with a cubic rock salt structure and with the preferential orientation (111) plane. The lattice parameter and crystallite size of the films are found as a=600 Å and 62 nm from the X-ray reflectivity data from the atomic force microscopy image, respectively. The band gap width of the films is determined as 2.84 eV. The optical parameters of the films such as refractive index, extinction coefficient, real and imaginary parts of dielectric constant are evaluated. Moreover, from the Hall measurements, electrical resistivity, conductivity carrier mobility, and carrier concentration of the films are determined as 3.722 Ω m, 0.268 Ω¯¹ m¯¹, 8.486× 10¯¹ m² V¯¹ s¯¹, and 1.976× 10^{18} m^{-3}, respectively.
17
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Structure Dependent Conductivity of Ultrathin ZnO Films

80%
Snigurenko D., Kopalko K., Krajewski T., Łuka G., Gierałtowska S., Witkowski B., Godlewski M., Dybko K., Paszkowicz W., Guziewicz E.
Acta Physica Polonica A
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2012
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vol. 122
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issue 6
1042-1044
EN
Zinc oxide films dedicated for hybrid organic/inorganic devices have been studied. The films were grown at low temperature (100°C, 130C and 200°C) required for deposition on thermally unstable organic substrates. ZnO layers were obtained in atomic layer deposition processes with very short purging times in order to shift a structure of the films from polycrystalline towards amorphous one. The correlation between atomic layer deposition growth parameters, a structural quality and electrical properties of ZnO films was determined.
18
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Reduction of the Optical Losses in CdTe/ZnTe Thin-Film Solar Cells

80%
Chusnutdinow S., Pietruszka R., Zaleszczyk W., Makhniy V., Wiater M., Kolkovsky V., Wojtowicz T., Karczewski G.
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vol. 126
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issue 5
1072-1075
EN
We report on reduction of optical losses in n-CdTe/p-ZnTe thin-film solar cells grown by molecular beam epitaxy. The investigated thin-film devices were grown from elemental sources on monocrystalline, semi-insulating, (100)-oriented GaAs substrates. The optical losses have been reduced by a texturing of the device surface and by depositing of a ZnO antireflection coating. Current-voltage and spectral characteristics of the investigated p-ZnTe/n-CdTe solar cells depend significantly on the preparation of the surface of the ZnTe window. We describe a procedure of chemical etching of the ZnTe window leading to surface texturing. A ZnO layer of proper thickness deposited by low-temperature atomic layer deposition technique on the ZnTe surface forms an effective antireflection coating that leads to the reduction of optical losses. Due to reduction of the optical losses we observe increase of the short-circuit current, J_{SC}, by almost 60% and of the energy conversion efficiency by 44%.
19
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Atomic Force Microscopy Study of a Voltage Effect on CdZnTe Crystal Dimensions

80%
Aleszkiewicz P., Wojciechowski T., Fronc K., Kolkovsky V., Janik E., Jakieła R., Mycielski A., Karczewski G., Aleszkiewicz M.
Acta Physica Polonica A
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2008
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vol. 114
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issue 5
1041-1047
EN
In this work we studied the influence of an external electric voltage on spatial dimensions of CdZnTe mixed crystals. In order to get an absolute magnitude of the sample thickness and to gain insight to the changes of lateral dimension, in quasi-bulk 3 μm thick CdZnTe layers grown by molecular beam epitaxy square craters were formed by ion sputtering in a secondary ion mass spectrometer. The vertical and lateral dimensions of the craters were studied by the atomic force microscopy. The atomic force microscopy measurement revealed that the thickness of the CdZnTe layer increases in a result of applying a single voltage pulse to the sample surface and decreases reversibly after applying reversely biased voltage. The voltage triggering was high enough to switch the conductivity state of the sample i.e., the effect of thickness change is accompanied by the effect of conductivity switching. The thickness change is significant, reaching several percents of the entire layer thickness.
20
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Anharmonic Optical Phonon Effects in ZnO Nanocrystals

80%
Khusnutdinov S., Dynowska E., Zaleszczyk W., Makhniy V., Wysmołek A., Korona K.
Acta Physica Polonica A
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2011
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vol. 119
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issue 5
678-680
EN
Zinc oxide (ZnO) is a very promising material for optoelectrical devices operating at the short-wavelength end of the visible spectral range and at the near UV. The Raman scattering studies of ZnO heterolayers formed by isothermal annealing show sharp phonon lines. In addition to the A_1(TO), E_1(TO), E_2^{H}, and E_1(LO) one-phonon lines, we observed two-phonon lines identified as: E_2^{H} - E_2^{L}, E_2^{H} + E_2^{L}, and 2LO at 332, 541, and 1160 cm^{-1}, respectively (at room temperature). The identification of the E_2^{H} - E_2^{L} peak was confirmed by its thermal dependence. Temperature dependent measurements in the range 6-300 K show that the phonon frequencies decrease with temperature. The E_2^{H} peak is at energy 54.44 meV (439.1 cm^{-1}), at 4 K and due to phonon-phonon anharmonic interaction, its energy decreases to 54.33 meV (438.2 cm^{-1}) at room temperature. The Grüneisen parameter found for this oscillation mode was γ_{E} 2H = 1.1 at about 300 K. The intensity of the E_2^{H} - E_2^{L} peak increases strongly with temperature and this dependence can be described by the Bose-Einstein statistics with activation energy of 13.8 meV (nearly equal to the energy of the E_2^{L} phonon).
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