MBE Growth and Properties of ZnTe- and CdTe-Based Nanowires

T. Wojtowicz,E. Janik,W. Zaleszczyk,J. Sadowski,G. Karczewski,P. D luZewski,S. Kret,W. Szuszkiewicz,E. Dynowska,J. Domagala,M. Aleszkiewicz,L. T. Baczewski,A. Petroutchik,A. Presz,W. Pacuski,A. Golnik 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

We review our results on the growth of ZnTe- and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)- and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was h111i, and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe- and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn2+ transition between crystal-field-split energy levels (4T1 → 6A1) was observed in the ZnMnTe nanowires. We review our results on the growth of ZnTe- and CdTe-based nanowires (NWs) and on their basic structural and optical properties. The nanowires were produced by using molecular beam epitaxy (MBE) with the use of a mechanism of catalytically-enhanced growth. The growth of ZnTe, CdTe, ZnMgTe and ZnMnTe nanowires was performed from elemental Zn, Cd, Mn, Mg and Te sources on the surfaces of (001)-, (110)- and (111)B-oriented GaAs substrates with Au nanocatalysts. The morphological and structural properties of the nanowires were assessed by using X-ray diffractometry, field-emission scanning electron microscopy, and high resolution transmission electron microscopy. Additional studies of the compositions of both the nanowires and the Au-rich nanocatalysts were performed with the use of energy dispersive X-ray spectroscopy. The optical properties of the NWs were assessed by using photoluminescence and Raman-scattering studies performed in both macro and micro modes. The studies revealed that binary and quaternary nanowires with average diameters from 30 to 70 nm and lengths from 1 to 2.6 µm were monocrystalline in their upper parts, their growth axis was h111i, and they grow along the [111] direction of the substrate, independent of the substrate orientation used. A Au-rich (with 20 % Ga) spherical nanocatalyst was always visible at the tip of a nanowire, thus indicating that a vapor-liquid-solid mechanism was responsible for the growth of the ZnTe- and the CdTe-based nanowires. The formation of homogeneous mixed crystal ZnMnTe and ZnMgTe nanowires was demonstrated by measurements of the variation of the lattice constant and by Raman experiments that revealed the expected shift and appearance of new phonon lines and a strong enhancement of the LO-phonon structures for an excitation close to the exciton energy of the NW materials. The photoluminescence from the internal Mn2+ transition between crystal-field-split energy levels (4T1 → 6A1) was observed in the ZnMnTe nanowires.

Magnetoresistance of Iodine-Doped CdMnTe/CdMgTe Spin Quantum Wells

V. Kolkovsky,M. Wiater,T. Wojtowicz,G. Karczewski,J. Jaroszynski 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

Single Cd1-xMnxTe quantum wells embedded in nonmagnetic Cd1-MgyTe barriers were grown by using molecular beam epitaxy (MBE). The Cd1-xMnxTenCd1-MgyTe structures were modulation doped by using iodine donors. The manganese (x) and the magnesium (y) contents were carefully adjusted to obtain the same values of the energy band gaps in both materials. A composition adjustment was achieved based on photoluminescence measurements. The magnetoresistance measurements were carried out in the temperature range from 1.6 K to 300 K and at magnetic fields up to 9 T. The analysis of the Hall effect measurements indicated that increasing of the magnetic eld caused the formation of a quantum well in the conduction band of the magnetic Cd1-MnxTe layer. This effect caused a transfer of quasi-free electrons from a 3D conducting channel located in the non-magnetic Cd1-MgyTe barriers to a magnetically-induced 2D quantum well. As expected, the electrons localized in the 2D conduction channel were highly mobile, which was manifested by the appearance of Shubnikov-de Haas oscillations.

Colossal Magnetoresistance in (Cd,Mn)Te heterostructures

T. Andrearczyk,W. Zaleszczyk,M. Wiater,T. Wojtowicz,M. Sawicki,G. Karczewski,T. Dietl,Dragana Popovic,J. Jaroszynski 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.1

We report on magnetotransport in diluted magnetic 2D modulation doped (Cd,Mn)Te quantum wells and 3D bulk (Cd,Mn)Se samples. The application of magnetic elds reveals features commonly observed in colossal magnetoresistant (CMR) materials, such as a strong negative magnetoresistance and dramatic and nonmonotonic changes in the zero-eld resistance, which coincide with the fer- romagnetic ordering. These phenomena are present near the metal-insulator transition (MIT), yet another common property of CMR systems. Most likely, the observed CMR-like features re ect nanoscale phase separation of the electron uid and the emergence of ferromagnetic clusters in an intermediate density region. Our results suggest that the clustering around the MIT is ubiquitous not only in CMR manganites and underdoped cuprates but also in disordered semiconductors. We report on magnetotransport in diluted magnetic 2D modulation doped (Cd,Mn)Te quantum wells and 3D bulk (Cd,Mn)Se samples. The application of magnetic elds reveals features commonly observed in colossal magnetoresistant (CMR) materials, such as a strong negative magnetoresistance and dramatic and nonmonotonic changes in the zero-eld resistance, which coincide with the fer- romagnetic ordering. These phenomena are present near the metal-insulator transition (MIT), yet another common property of CMR systems. Most likely, the observed CMR-like features re ect nanoscale phase separation of the electron uid and the emergence of ferromagnetic clusters in an intermediate density region. Our results suggest that the clustering around the MIT is ubiquitous not only in CMR manganites and underdoped cuprates but also in disordered semiconductors.

Selection of Bacteria Capable of Dissimilatory Reduction of Fe(III) from a Long-term Continuous Culture on Molasses and Their Use in a Microbial Fuel Cell

( Radoslaw Sikora ),( Elzbieta Grzesiuk ),( Sikora Anna ),( Justyna Wojtowicz Sienko ),( Piotr Piela ),( Urszula Zielenkiewicz ),( Karolina Tomczyk Zak ),( Aleksandra Chojnacka ),( Pawe Kowalczyk ),( 한국미생물 · 생명공학회 2011 Journal of microbiology and biotechnology Vol.21 No.3

Ferric ion-respiring microorganisms (FRMs) are a group of prokaryotes that use Fe(III) as well as other metals as terminal electron acceptors in the process of anaerobic respiration. Special attention is paid to a biotechnological significance of FRMs because of their potential role in electricity production in microbial fuel cells (MFCs) where the terminal acceptor of the electrons during anaerobic respiration is not a ferric ion but the anode. One of the best known FRMs is the Shewanellaceae family. Most of the Shewanella species have been isolated from marine environments. In this report, sugar beet molasses and ferric oxide were successfully used in the selection of a bacterial consortium capable of dissimilatory Fe(III) reduction in a long-term continuous culture. The inoculum was a sample of eutrophic lake bottom sediment. Among the bacteria present in this culture were representatives of the Enterobacteriaceae, and the genera Pseudomonas, Arcobacter, and Shewanella. Two non-marine Fe(III)-reducing Shewanella-related clones named POL1 and POL2 were isolated. The abilities of the POL1 and POL2 isolates to metabolize a panel of 190 carbon sources were examined using a BIOLOG assay. The results confirmed the abilities of the shewanellas to utilize a broad range of carbon substrates. The utility of the POL1 and POL2 isolates in H-type MFCs operating on pyruvate or molasses was demonstrated. The operation of the MFC with shewanellas cultured on molasses was shown for the first time. A two-stage character of the fuel cell polarization curves, not previously noted in Shewanella MFC studies, was observed.

Photovoltaic characterization of n-CdTe/p-CdMnTe/GaAs diluted magnetic diode

I.S. Yahia,F. Yakuphanoglu,S. Chusnutdinow,T. Wojtowicz,G. Karczewski 한국물리학회 2013 Current Applied Physics Vol.13 No.3

A CdTe/CdMnTe heterojunction magnetic diode for photovoltaic applications was fabricated by using molecular beam epitaxy (MBE). The ideality factor and the potential barrier height of the diode were determined to be 1.25 and 0.836 eV, respectively. Photovoltaic parameters of the studied device were determined at various illumination intensities. The highest open circuit voltage of the CdTe/CdMnTe heterostructure was equal to 0.56 V at the illumination intensity of 130 mW/cm2. The reverse current of the n-CdTe/p-CdMnTe/GaAs diode increases with the increasing illumination intensities. The obtained results suggest that n-CdTe/p-CdMnTe/GaAs diode can be used as a photodiode in photovoltaic and photodetector applications.

Ferromagnetic III-Mn-V Semiconductors: Manipulation of Magnetic Properties by Annealing, Extrinsic Doping, and Multilayer Design

J. K. Furdyna,I Kuryliszyn,K. M. Yu,S Lee,T Wojtowicz,W Walukiewicz,W. L. Lim,X Liu,Y Sasaki 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.III

Modulation of Quantum Well Optical Properties by Illumination above the Barrier Bandgap

D. Wolverson,A. V. Koudinov,Yu. G. Kusrayev,L. C. Smith,J. J. Davies,M. Wiater,G. Karczewski,T. Wojtowicz 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

The spin flip Raman scattering signals associated with the Mn2+ 3d5 electrons in a range of CdTe-based dilute magnetic semiconductor quantum well structures is shown to be sensitive to even very weak above-barrier illumination, as are the quantum-well photoluminescence from exciton and trion recombination and acoustic phonon Raman scattering signals excited in resonance with the quantum well. This surprising degree of sensitivity is discussed in terms of the modulation of the carrier densities in the quantum wells, leading to a modulation of the resonant intermediate state for Raman scattering and, therefore, of the scattering cross section. Depending on the majority intrinsic carrier type in the quantum wells, we show that either enhancing or quenching of the Raman signals can result.

Changes of the Light-Hole Exciton Line in CdMnTe/CdMgTe Quantum Wells Under Resonant Excitation of the Heavy-Hole Exciton

Artur Trajnerowicz,Andrzej Golnik,Piotr Kossacki,Wojciech Pacuski,Witold Bardyszewski,Maciej Wiater,Grzegorz Karczewski,Tomasz Wojtowicz 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

Systematic studies of excitonic lines in the strong excitation regime were carried out by using a pump-probe method. Several samples containing quantum wells with different well widths (from 80 Å to 160 Å) were investigated. Most of the quantum wells were intentionally undoped but contained a 2D gas of free holes. The density of the free holes could be varied by changing the intensity of additional illumination. After resonant excitation of the heavy-hole exciton ground state by using an intense pump pulse we observed changes in the heavy- and the light-hole exciton lines. The resonant creation of a high population of e1hh1 excitons caused energetic blue shifts of the e1lh1 excitons. The blue shift in the experiment with opposite circularly-polarized pump and probe pulses could be explained as an interaction of electrons of the same spin bounded into the e1hh1 and the e1lh1 excitons. Model calculations of absorption showed qualitative agreement with the experimental data.

Linearly Polarized Emission of Quantum Wells Subject to an In-Plane Magnetic Field

D. Wolverson,Yu. G. Kusrayev,A. V. Koudinov,N. S. Averkiev,J. J. Davies,J. Kossut,G. Karczewski,T. Wojtowicz 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5

We present results on the linear polarization of the photoluminescence (PL) of dilute magnetic semiconductor quantum wells which is induced by an applied magnetic field. The PL is found to be partially linearly polarized, but without any correlation with the polarization of the exciting light, whilst the direction of the polarization does not depend on the direction of the magnetic field in the plane although its magnitude does. We present a model for this behavior in terms of a possible reduction of the in-plane symmetry of the quantum well; we conclude that any perturbations giving (i) a finite in-plane hole g-factor and (ii) a mixing of light and heavy holes are sufficient to generate the type of experimental behavior we observe.