Acta Physica Polonica A

AC T A PH Y S I C A PO L O N I C A A

Vol. 92 No 5 November'97

MAGNETOTRANSPORT AND MAGNETOOPTICS OF InAs_{1-x}Sb_x AND HETEROJUNCTIONS COMBINATIONS FORMED BETWEEN InAs AND GaSb, AlSb OR InAs_{1 -x}Sb_x

R.A. Stradling

Blackett Laboratory, Imperial College of Science, Technology & Medicine London SW7 2BZ, UK

Cyclotron resonance and interband measurements are reported in magnetic fields up to 160 T for InAs/InAs_{1-x}Sb_x superlattices, one of which is a ``self-organised'' or ``natural'' superlattice, and InAs_{1-x}Sb_x epilayers. The samples were grown by MBE at temperatures between 370^\circC to 500^\circC. No dependence of the band gap, effective masses or g-values on the growth temperature was detected. Anomalous tilt behaviour was observed for the superlattices. Inversion asymmetry induced spin-splitting of the subbands in gated InAs quantum wells is investigated by means of the Shubnikov-de Haas effect and cyclotron resonance. The non-parabolicity was well fitted by Kane theory, although the measured values of effective mass were substantially higher than predictions. Infrared life time measurements at wavelengths between 6 and 85 microns are undertaken with free electron lasers on InAs/InAs_{1-x}Sb _x superlattices and InAs/AlSb quantum wells. Suppression of the Auger recombination times is demonstrated with the superlattices.
PACS numbers: 72.20.My, 76.40.+b, 78.20.Ls

DIELECTRIC FUNCTION THEORY CALCULATIONS OF POLARITONS IN GaN

K.P. Korona, R. Stepniewski and J.M. Baranowski

Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warszawa, Poland

Properties of polaritons (free excitons coupled with photons of similar energy) in gallium nitride are investigated by performing calculations based on dielectric function theory including all three excitons A, B and C (characteristic for the wurtzite structure). Moreover the excited states of excitons have been taken into account by adding Elliott's components to dielectric function. Energies, polarizabilities and damping constants of excitons are determined. It is shown that due to inter-exciton interactions the B and C excitons are strongly damped. It is estimated that the characteristic time of B to A relaxation is t_{BA}=1 ps. The exciton C lifetime is estimated \tau_C=0.2 ps.
PACS numbers: 71.36.+c, 78.66.Fd

STIMULATED EMISSION in Zn(Se,S) SINGLE CRYSTALS

L. Kowalczyk, A. Mycielski, A. Szadkowski

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland

C. Testelin, C. Rigaux and M. Menant

Groupe de Physique des Solides, Universites Paris VI et Paris VII Tour 23, 2 place Jussieu, 75251 Paris Cedex 05, France

Two different types of optically pumped stimulated emission were observed at 1.8 K in the high quality Zn(Se,S) crystals grown by low temperature physical vapour transport. One type, occurring at moderate excitation levels, is ascribed to the recombination of excitons localized because of chemical disorder in the two-anion mixed crystal. The other type, occurring at high excitation levels, is related to the inelastic exciton-exciton scattering.
PACS numbers: 78.45.+h, 78.55.Et, 81.10.Bk

4f SHELL OF Gd^{2+} AND Gd^{3+} IONS IN Sn_{1-x}Gd_xTe - RESONANT PHOTOEMISSION STUDY

B.J. Kowalski, Z. Golacki, E. Guziewicz, B.A. Orlowski

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

and R.L. Johnson

Universitat Hamburg, II Institut fur Experimentalphysik Luruper Chausse 149, 22761 Hamburg, Germany

Resonant photoemission spectra of Sn_{1-x}Gd_xTe (x=0.02 and 0.08) measured for the photon energy range 142 to 151 eV show the valence band density of states distribution and the Gd 4f derived maximum. The energy position of the J=0 component of the Gd 4f maximum was determined and used as a measure of the Gd 4f shell binding energy. The electrostatic model of core level shifts was used to interpret the difference in the Gd 4f binding energies observed for x=0.02 and x=0.08.
PACS numbers: 71.20.-b, 79.60.-i

INFRARED LUMINESCENCE IN Er AND Er+O IMPLANTED 6H SiC

A. Kozanecki

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

W. Jantsch, W. Heis, G. Prechtl

Johannes Kepler Universitat, 4040, Linz, Austria

B.J. Sealy and C. Jeynes

Surrey Centre for Research in Ion Beam Applications, University of Surrey Guildford, Surrey, GU2 5XH, UK

Photoluminescence in the neighbourhood of 1.54 \mum due to the \linebreak \pz4I{13/2}-\pz4I{15/2} intra-4f-shell transitions of Er^{3+} ions in 6H SiC is studied. Effects of oxygen coimplantation is also investigated. No difference in the photoluminescence spectra of Er only and Er+O implanted SiC was found. It is concluded that the emission around 1.54 \mum in SiC:Er originates from erbium-oxygen complexes, which are formed as a result of thermal annealing.
PACS numbers: 61.72.Ww, 71.55.-i, 78.55.-m

LIGHT-INDUCED GRATINGS IN CdMnTeSe:In CRYSTALS

B. Koziarska-Glinka^a, M. Ponder^a, T. Wojtowicz^a, I. Miotkowski^b, J.M. Langer^a and A. Suchocki^a

^a Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland
^b Purdue University, West Lafayette, Indiana, 46 566, USA

We show that DX-like centers in Cd_{1-x}Mn_xTe_{1-y}Se _x:In crystal can be used in writing volume holographic gratings. The scattering efficiency is higher than 10% which proves the dispersive character of the light-induced gratings. Two different metastable centers with different lattice relaxation were found in the crystal. Measurements of the power dependence of the degenerate four-wave mixing scattering efficiency testify that both of these centers have negative U properties.
PACS numbers: 74.62.Dh, 61.72.Ji, 42.65.Hw

HALF-PARABOLIC QUANTUM WELLS OF DILUTED MAGNETIC SEMICONDUCTOR Cd_{1-x} Mn_xTe

M. Kutrowski, T. Wojtowicz, G. Cywinski, G. Karczewski, E. Janik, E. Dynowska, J. Kossut

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

P. Kossacki

Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland

R. Fiederling, A. Pfeuffer-Jeschke and W. Ossau

Physikalisches Institut der Universitat Wurzburg, 97074 Wurzburg, Germany

We report on magnetooptical studies of MBE-grown half-parabolic \linebreak CdTe/Cd_xMn_{1-x}Te quantum well structures. The value of the valence band offset Q_v=0.4\pm 0.05 was determined by comparing energies of optical transitions in the absence of a magnetic field with model calculations. This value was verified by fitting the observed spin splitting of the lowest heavy hole (hh) state. We discuss also the temperature dependence of Q_v.
PACS numbers: 78.66.Hf, 75.50.Pp

MAGNETIC FIELD DEPENDENCE OF PHONON-INDUCED DRAG CURRENT OF 2D CARRIERS

D. Lehmann

Institut fur Theoretische Physik, Technische Universitat Dresden 01062 Dresden, Germany

Cz. Jasiukiewicz and T. Paszkiewicz

Institute of Theoretical Physics, University of Wroclaw Pl. Borna 9, 50-205 Wroclaw, Poland

The magnetic field dependence of the drag current induced by beams of acoustic phonons is studied in a 2D gas of carriers, formed in a heterostructure. This drag current is related to the velocity of the center of mass of the gas. The elimination of the degrees of freedom related to the relative motion of the carriers leads to a Langevin equation for the center-of-mass position vector. From this equation one can obtain an expression for the induced current density which depends on carrier density-density correlation functions. An explicit formula for the time-integrated current density is derived taking into account all intra and inter Landau level transitions. Corresponding numerical results are in good agreement with the experimental patterns.
PACS numbers: 63.20.Kr, 73.40.-c

EXCITONIC EFFECTS IN LINEAR AND PHOTOINDUCED FARADAY ROTATION IN SEMIMAGNETIC SEMICONDUCTORS

P. Leisching^{a,b}, R. Pankoke^a, C. Buss^a, R. Frey^a, C. Flytzanis^a, J. Cibert^c and A. Wasiela^c

^a Ecole Polytechnique, Laboratoire d'Optique Quantique du C.N.R.S. 91128 Palaiseau Cedex, France
^b Max-Born-Institute, Rudower Chaussee 6, 12489 Berlin, Germany ^cLab. de Spectrometrie Physique, Universite Joseph Fourier-Grenoble and C.N.R.S. 38402 St. Martin d'Heres Cedex, France

We investigate the influence of the Coulomb interaction on the giant linear and photoinduced Faraday rotation in the bulk Cd_{1-x}Mn_xTe system. Experimental results are presented and discussed by calculating the complex dielectric function. The anisotropy and k-dependence of the magnetic spin-exchange interaction and the Coulomb interaction between optically excited bound and unbound electron-hole pairs are considered using a microscopic theory. At high excitation densities, the excitonic nonlinearities of the 1s transitions are investigated.
PACS numbers: 78.66.Hf, 78.20.Ls, 75.30.Et, 42.65.-k

VIBRATIONAL MODES IN Si_xGe_{1-x} ALLOYS: TEMPERATURE AND COMPOSITIONAL DEPENDENCE

M. Lorenc and J. Humlicek

Faculty of Science, Department of Solid State Physics, Masaryk University Kotlarska 2, 611 37 Brno, Czech Republic

We report infrared absorption spectra of crystalline Si_xGe_{1-x} alloys with silicon content 0\le x\le1 at room and liquid nitrogen temperature. We covered the spectral range from 375 to 1200 cm^{-1} that includes the ``Si-Ge'' and ``Si-Si'' single-phonon transitions, the continuum of two-phonon processes, and the localized mode of interstitial oxygen. We study the change of vibrational structure and correlation between reference (pure Si and Ge) and alloy spectra. We observed shifts to lower wave numbers by about 1 cm^{-1} of the two-phonon absorption bands per 1% increase in germanium concentration. Pronounced changes of the vibrational spectra upon lowering the temperature were detected.
PACS numbers: 78.30.Am, 63.20.Dj

THEORETICAL ANALYSIS OF OPTICAL GAIN IN QUANTUM WELL LASERS INCLUDING VALENCE-BAND MIXING EFFECT

S.P. Lepkowski and M. Bugajski

Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland

The linear optical gain in the AlGaAs/GaAs quantum well lasers is studied theoretically, taking into account the valence-band mixing effect. Our approach is based on the multiband effective-mass theory (k p method) and the density-matrix formalism. In order to obtain the valence bands' structure we employ the 4\times4 Luttinger-Kohn Hamiltonian, neglecting the coupling to the split-off band. The spectral dependence of the linear optical gain is calculated using the density-matrix method with interband relaxation. Finally, we analyse the spatial distribution of the optical gain in the quantum well region for the photon energy corresponding to the peak value of the linear gain.
PACS numbers: 42.55.Px, 73.20.Dx

BOUND-TO-CONTINUUM TRANSITIONS IN QUANTUM WELL WITH CAPPING BARRIER LAYER OF FINITE SIZE

C. Nalewajko and M. Zaluzny

Department of Theoretical Physics, Maria Curie-Sklodowska University Pl. M. Curie-Sklodowskiej 1, 20-031 Lublin, Poland

It was shown employing the functional density approach that interference effects resulting from finite size of the cap layer can modify substantially the absorption line shape connected with bound-to-continuum intraband transitions in quantum wells.
PACS numbers: 78.30.Fs, 73.20.Dx

INFLUENCE OF INTERFACE-INDUCED DISORDER ON CLASSICAL AND QUANTUM CONDUCTIVITY OF CdTe:IN EPITAXIAL LAYERS

J. Lusakowski, K. Karpierz, M. Grynberg

Institute of Experimental Physics, University of Warsaw Hoza 69, 00-681 Warsaw, Poland

G. Karczewski, T. Wojtowicz

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

S. Contreras and O. Callen

Groupe d'Etude des Semiconducteurs, Universite Montpellier II Pl. E. Bataillon, Montpellier, France

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.
PACS numbers: 73.61.Ga, 73.50.Jt

CHANGES OF ELECTRONIC STRUCTURE OF SnTe DUE TO HIGH CONCENTRATION OF Sn VACANCIES

J. Masek and D.N. Nuzhnyj

Institute of Physics, Academy of Sciences of the Czech Republic Na Slovance 2, 180 40 Praha 8, Czech Republic

Non-stoichiometric Sn_{1-y}Te is a strongly degenerated n-type semiconductor. This is important for understanding unusual features of magnetic behaviour of Sn_{1-x}Gd_xTe where the relative positions of the Fermi energy and the atomic d-level of Gd govern the exchange coupling. The influence of the Sn vacancies on the band structure cannot be neglected if their concentration reaches a few atomic percent. We address this problem by using a tight-binding coherent potential approach and show that although the character of the bands remains unchanged, they are modified so that \varepsilon_d can come out above the heavy-hole band.
PACS numbers: 71.20.Nr, 71.55.Jv

INFRARED OPTICAL AND X-RAY DETERMINATION OF PARAMETERS FOR MOVPE GROWN InAs_{1-x}Sb_x EPILAYERS

B. Marszalek, E. Zielinska-Rohozinska, R. Bozek, R. Stepniewski and A.M. Witowski

Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw, Poland

The experimental room-temperature transmission of metalorganic vapour phase epitaxy grown InAsSb epilayers is compared with calculations based on a Kane model of the band structure. The band structure parameters are found. The composition of the samples was determined by X-ray diffraction.
PACS numbers: 71.20.-b, 78.20.-e, 78.30.-j

BINDING OF BIEXCITONS IN GaAs/AlGaAs SUPERLATTICES

V. Mizeikis

Institute of Material Research and Applied Science, Vilnius University Sauletekio Ave. 9, build. III, 2054 Vilnius, Lithuania

D. Birkedal, W. Langbein, V.G. Lyssenko and J.M. Hvam

Mikroelektronik Centret, The Technical University of Denmark 2800 Lyngby, Denmark

Binding of the heavy-hole excitons and biexcitons in GaAs/Al_{0.3}Ga_{0.7}As superlattices is studied using linear and nonlinear optical techniques. High biexciton binding energies characteristic of quasi two-dimensional biexcitons are observed in superlattices with considerable miniband dispersion.
PACS numbers: 71.35.Cc, 78.66.Hf, 42.50.Md

TRANSMISSION AND REFLECTION OF MILLIMETER WAVES IN i-GaAs/n-GaAs PERIODIC STRUCTURES IN VOIGT CONFIGURATION

R. Narkowicz, R. Brazis and L. Safonova

Semiconductor Physics Institute, A. Gostauto 11, 2600 Vilnius, Lithuania

The paper presents the first experimental results on the in-plane propagation of millimeter waves in GaAs {\em\ldots n-i-n-i-\ldots} type periodic layered structures in the Voigt geometry. The data are found to agree with theoretical calculations based on the effective medium approximation, showing the feasibility of contactless non-destructive probing of periodic layered structures.
PACS numbers: 78.66.-w

EFFECT OF EPITAXIAL LAYER THICKNESS ON BUILT-IN ELECTRIC FIELD IN REGION OF AlGaAs/SI-GaAs INTERFACE: A PHOTOREFLECTANCE STUDY

T.J. Ochalski, J. Zuk

Institute of Physics, M. Curie-Sklodowska University Pl. M. Curie- Sklodowskiej 1, 20-031 Lublin, Poland

and L.A. Vlasukova

Institute of Applied Physics, State University, Minsk, Belarus

We present a study of detailed line shapes of photoreflectance spectra for Al_{0.3}Ga_{0.7} As/SI-GaAs epitaxial layers grown by MBE. All measurements were performed at 80 K under UHV conditions with a special care for the samples surface quality. A set of the photoreflectance spectra was collected for photon energies close to the GaAs and Al_{0.3}Ga_{0.7}As band gaps (E_0). The photoreflectance spectra originated in the vicinity of the Al_{0.3}Ga_{0.7}As/SI-GaAs interface were analyzed using the complex Airy function model of Franz-Keldysh oscillations. To examine the effect of the epitaxial layer thickness on parameters characterizing the interface, a step-by-step chemical etching was applied for stripping the top layers. The built-in electric field intensity, field inhomogeneity and phenomenological broadening parameter for interface regions were determined as a function of the epilayer thickness.
PACS numbers: 78.66.Fd, 78.20.-e

SPIN-ORBIT-COUPLING, ELECTRIC-FIELD AND FREE-CARRIER-SCREENING EFFECTS ON VALENCE BAND STRUCTURE OF STRAINED COUPLED QUANTUM WELLS

B. Olejnjkova

Institute of Electrical Engineering, Slovak Academy of Sciences Dubravska cesta 9, 842 39 Bratislava, Slovakia

We have calculated the structure of the valence bands and its dependence on the electric field and the density of free carriers in a lattice mismatched single and double quantum well. Our calculation is based on simultaneous solving of the effective mass equation for the envelope functions and Poisson's equation. The 6\times6 Luttinger-Kohn Hamiltonian is diagonalized into two 3\times3 blocks by a unitary transformation. We have shown how including the coupling between spin-orbit split-off band and light- and heavy-hole bands influences the shape of the valence bands. Further it has been found that at high densities of the free carriers and at non-zero electric field, the free-carrier screening affects the valence band structure and wave functions. This effect is considerably pronounced in double quantum well because of large spreading of the quantum states. The studying of the above effects is useful for band-structure engineering. {73.40.Kp, 73.20.Dx

ACTIVATED TRANSPORT IN MAGNETIC-FIELD INDUCED INSULATING PHASE IN TWO-DIMENSIONAL ELECTRON GAS IN InGaAs/InP HETEROSTRUCTURES

B. Podor, G. Gombos

Research Institute for Technical Physics of the Hungarian Academy of Sciences Budapest, Hungary

G. Remenyi

CNRS Centre de Recherche sur les Tres Basses Temperatures et Laboratoire des Champs Magnetiques Intenses, Grenoble, France

Gy. Kovacs

Applied Physics Research Group, Department of General Physics Lorand Eotvos University, Budapest, Hungary

I.G. Savel'ev and S.V. Novikov

Ioffe Physical-Technical Institute of the Russian Academy of Sciences St. Petersburg, Russia

We report on experiments on low temperature (millikelvin range) activated magnetotransport on low-density two-dimensional electron systems in InGaAs/InP for Landau level filling factors 0.25\le\nu \le0.55. The activation energy increases approximately linearly with decreasing filling factor. The observations are discussed in the light of the formation of the Wigner solid.
PACS numbers: 73.20.Dx

PHOTOIONIZATION OF Ge^-DX STATE IN GaAs

R. Piotrzkowski and L.H. Dmowski

High Pressure Research Center, Polish Academy of Sciences Sokolowska 29/37, 01-142 Warszawa, Poland

We have determined the efficiency of photoionization of Ge^-DX state in GaAs as a function of photon energy. The optical ionization energy derived from the fitting is about 1.0 eV. It proves a large difference between optical and thermal ionization energies and confirms that for Ge-impurity, the broken-bond model and large lattice relaxation are valid and not the breathing mode with small lattice relaxation, resulting from the calculations presented for Ge-impurity in T.M. Schmidt, A. Fazzio, M.J. Caldas,

EXCITON STATES IN TYPE-II ZnSe/BeTe QUANTUM WELLS

A.V. Platonov^a, D.R. Yakovlev^{a,b}, U. Zehnder^b, V.P. Kochereshko^a, W. Ossau^b, F. Fischer^b, Th. Litz^b, A. Waag^b and G. Landwehr^b

^a A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences St. Petersburg, Russia
^b Physikalisches Institut der Universitat Wurzburg, 97074 Wurzburg, Germany

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.
PACS numbers: 78.66.Hf, 78.20.Ls

HIGH RESISTIVITY GaN SINGLE CRYSTALLINE SUBSTRATES

S. Porowski, M. Bockowski, B. Lucznik, I. Grzegory, M. Wroblewski, H. Teisseyre, M. Leszczynski, E. Litwin-Staszewska, T. Suski

High Pressure Research Center, Polish Academy of Sciences Sokolowska 29/37, 01-142 Warsaw, Poland

P. Trautman, K. Pakula and J. Baranowski

Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland

High resistivity 10^4{-}10^6 \Omega cm (300 K) GaN single crystals were obtained by solution growth under high N_2 pressure from melted Ga with 0.1-0.5at.% of Mg. Properties of these crystals are compared with properties of conductive crystals grown by a similar method from pure Ga melt. In particular, it is shown that Mg-doped GaN crystals have better structural quality in terms of FWHM of X-ray rocking curve and low angle boundaries. Temperature dependence of electrical resistivity suggests hopping mechanism of conductivity. It is also shown that strain free GaN homoepitaxial layers can be grown on the Mg-doped GaN substrates.
PACS numbers: 71.55.Eq, 72.80.Ey

EFFECT OF NONEQUILIBRIUM PLASMONS ON ELECTRON-PLASMON INTERACTIONS IN SEMICONDUCTORS

V.V. Popov and T.Yu. Bagaeva

Institute of RadioEngineering and Electronics of the Russian Academy of Sciences Saratov Branch, Zelyonaya 38, Saratov 410019, Russia

The effect of nonequilibrium plasmons on the steady-state high-dc-field response of electron gas in n-GaAs is numerically studied via iterative procedure using the Monte Carlo simulation algorithm for hot-electron transport and the Boltzmann equation for plasmons. The electron population inversion in wave vector space along the electric field is predicted to exist for fields in excess of about 10 kVcm. The plasmon distribution disturbances leave the steady-state velocity at low fields almost unaffected but lead to reduction of that up to 10% for fields around and above the maximum of the velocity-field characteristics.
PACS numbers: 71.45.Gm, 72.10.Di

STRUCTURAL AND ELECTRICAL PROPERTIES OF LOW CONCENTRATION SnTe LAYERS AND PbTe/SnTe HETEROSTRUCTURES GROWN BY MBE

J. Sadowski^{a,b}, E. Grodzicka^a, E. Dynowska^a, J. Adamczewska^a, J. Domagala^a and W. Przedpelski^a

^a Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland
^b Institute of Vacuum Technology, Dluga 44/50, 00-241 Warsaw, Poland

We analyse properties of thin SnTe layers and PbTe/SnTe heterostructures grown by MBE on BaF_2(111) substrates. Reflection high energy electron diffraction patterns registered during MBE growth of the samples as well as post-growth X-ray diffraction measurements evidence a high structural perfection of 0.6 \mum thick SnTe layers and (50 \AA PbTe)/(50 \AA SnTe) superlattices. The full width at half maximum values of (222) X-ray rocking curves measured for these thin SnTe layers crystallized in the optimal MBE growth conditions are about 300 arcsec; the carrier concentrations can be tuned from 5\times10^{19} cm^{-3} to 10^{2 1} cm^{-3} depending on the MBE process parameters.
PACS numbers: 81.15.Gh, 61.14.Hg

FIRST X-RAY EVIDENCE OF HETEROGENEOUS IMPURITY CORRELATIONS IN VERY HIGHLY DOPED n-GaAs

T. Slupinski and E. Zielinska-Rohozinska

Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warszawa, Poland

Measurements of X-ray scattering from very highly doped GaAs:Te single crystals as a function of doping level and thermal treatment (annealing temperature) are reported. Reversible diffuse X-ray scattering occurs after sample annealing below a certain temperature. Presented results indicate an inhomogeneous arising of impurity-impurity correlations in GaAs:Te solid solution. Observed features of diffuse X-ray scattering in reciprocal space can be well understood within Krivoglaz theory of scattering due to spatial fluctuations of solute atoms pair correlation function and related lattice deformations. Good coincidence of diffuse X-ray scattering with the free electron concentration changes caused by an annealing is reported. Free electron concentration drop accompanying impurity correlation strongly suggests a certain form of impurity bonding.
PACS numbers: 61.72.-y, 61.10.-i, 71.55.-i

DIRECT MEASUREMENTS OF BOUND MAGNETIC POLARON MAGNETIZATION IN Ga-DOPED Cd_{1-x}Mn_xTe

J. Stankiewicz, F. Palacio

Instituto de Ciencia de Materiales de Aragon, Consejo Superior de Investigaciones Cientj ficas and Universidad de Zaragoza, 50009-Zaragoza, Spain

and F. Villuendas

Departamento de Fj sica Aplicada, Universidad de Zaragoza, 50009-Zaragoza, Spain

Light induced remanent changes in magnetization of n-type Cd_{1-x}Mn_x Te (x=0.01, 0.05) single crystals have been measured at T=2 and 5 K and in magnetic fields of up 0.5 T. The effect observed gradually saturates with increasing magnetic field. It also correlates with light induced increase in shallow donor concentration measured on the same samples. The bound magnetic polaron theory accounts for the temperature and magnetic field variations of the persistent magnetization. There are no fitting parameters.
PACS numbers: 75.50.Pp

IN-PLANE/TILTED MAGNETIC-FIELD-DEPENDENT CONDUCTANCE OF 2D ELECTRON SYSTEMS IN ASYMMETRIC DOUBLE QUANTUM WELLS

L. Smrcka, P. Vasek, T. Jungwirth, O.N. Makarovskii, M. Cukr

Institute of Physics, Academy of Science of the Czech Republic Cukrovarnicka 10, 162 00 Prague 6, Czech Republic

and L. Jansen

Grenoble High Magnetic Field Laboratory, B.P. 166, 38042 Grenoble Cedex 9, France

The resistance in an asymmetric double-well structure was measured as a function of magnetic fields oriented almost parallel to the plane of the electron layer. It was shown that the shape of the magnetoresistance curves is close to the in-plane magnetic-field-dependent density of states which we obtained by self-consistent numerical calculation. The novel feature is the negative magnetoresistance observed at low magnetic fields.
PACS numbers: 72.20.My, 73.40.Kp

MAGNETIC PROPERTIES OF EuS/PbS SEMICONDUCTING STRUCTURES

A. Stachow-Wojcik, A. Twardowski

Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland

T. Story, W. Dobrowolski, E. Grodzicka

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

and A. Sipatow

Kharkov State Technical University, Kharkov, Ukraine

We report results of magnetization study of EuS/PbS superstructures with different thicknesses of magnetic and nonmagnetic layers. Reduction of ferromagnetic phase transition temperature was found with decreasing EuS thickness. Reasonable description of this effect is obtained within the model based on the mean field approximation.
PACS numbers: 75.50.Pp

STUDY OF DI-HYDROGEN-MONOVACANCY DEFECT IN SILICON

P. Stallinga and B.B. Nielsen

Institut for Fysik og Astronomi, \AA rhus University Ny Munkegade, bygning 520, 8000 \AA rhus-C, Denmark

A careful analysis of the alleged electron paramagnetic resonance spectrum of VH_2 in silicon is made. The parameters of this spectrum coincide with those of the well-known excited state (S=1) spectrum of the oxygen vacancy defect. The conclusion is reached that they are one and the same.
PACS numbers: 76.30.-v, 76.30.Lh, 76.70.Hb

EXCITON IN 2D CUBIC INCLUSION IN HEXAGONAL GaN

M. Suffczynski

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

R. Stepniewski and J.M. Baranowski

Institute of Experimental Physics, Warsaw University, Hoza 69, 00-681 Warsaw, Poland

An inclusion of cubic GaN in an otherwise hexagonal matrix is considered to be equivalent to an effective quantum well. The exciton binding energy in a quantum well of a finite potential barrier height in the conduction and valence bands is calculated in the effective mass approximation with a variational envelope function type of Bastard and Takagahara. The exciton binding energy and the energy of exciton recombination line are computed, as a function of the well width, for realistic potential barrier heights and band-offset ratios.
PACS numbers: 73.20.Dx, 78.66.-w, 61.72.Nn

TRANSPORT AND MAGNETIC STUDY OF Gd IONS IN Pb_{1-y}Sn_yTe

T. Story et al.

Institute of Physics Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

Electric conductivity, Hall effect and magnetic susceptibility of Pb_{1-x-y} Sn_yGd_xTe mixed crystals with 0.13\le y\le0.93 and 0.001\le x\le0.04 were experimentally studied over the temperature range 4K \le T\le300 K. The incorporation of Gd ions into the Pb_{1-y}Sn_yTe matrix results in semi-metallic n-type conductivity of the crystals with y<0.6. For crystals with y>0.6 one observes only semi-metallic p-type conductivity. We present a model explaining these results in terms of the Sn composition dependence of the location of Gd^{2+/3+} level with respect to the band edges of PbSnGdTe.
PACS numbers: 75.20.Ck, 75.30.Et

ELECTRICAL AND ESR STUDIES OF GaN LAYERS GROWN BY METAL ORGANIC CHEMICAL VAPOUR DEPOSITION

B. Suchanek^a, M. Palczewska^b, K. Pakula^a, J. Baranowski^a and M. Kaminska^a

^a Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland
^b Institute of Technology of Electronic Materials Wolczynska 133, 01-919 Warsaw, Poland

Electrical transport and ESR studies were performed on the state-of-theart GaN layers grown on sapphire substrate using metal organic chemical vapour deposition technique. For undoped samples electron concentration below 2\times10^{17} cm^{-1} and mobility up to 500 cm^2/ (V s) were achieved whereas hole concentration up to 7\times10^{17} cm^{- 3} and mobility about 16 cm^2/(V s) were obtained for intentionally Mg doped samples and subsequently annealed. Temperature dependence of mobility was discussed. ESR revealed the presence of two resonance absorption lines. One of them with g_\perp=1.9487 and g_\parallel=1.9515, commonly observed in n-type GaN was due to shallow donor. The second ESR line was an isotropic one of g=2.0032 and it is discussed.
PACS numbers: 72.80.Ey, 73.61.Ey

PHOTOSTRICTION OF CdF_2:In CRYSTALS

A. Suchocki, J. Rauluszkiewicz, J.M. Langer and B. Koziarska-Glinka

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-666 Warsaw, Poland

Lattice relaxation accompanying phototransformation of In bistable centers from the ground, deep state to the shallow state in CdF_2 crystal has been measured with the use of scanning tunnelling microscope. It is shown that relatively small macroscopic changes of the crystal length in the order of 1.8\times10^{-6} accompany the phototransformation of In ions. Lattice expansion upon the influence of population of shallow donor levels in CdF_2 explains the observed small changes of lattice constant during the process.
PACS numbers: 61.16.Ch, 61.72.Hh, 74.62.Dh

TRANSITION METAL IMPURITIES AND ELECTRONIC STRUCTURE OF ZnSe-BASED ISOVALENT SEMICONDUCTOR ALLOYS

T.P. Surkova^a, W. Giriat^b, M. Godlewski^c and S. Permogorov^d

^a Institute of Metal Physics, Ural Division of Russian Academy of Sciences 620219 Ekaterinburg GSP-170, Russia
^b IVIC, Centro de Fisica, Apto 1827, Caracas 1010A, Venezuela
^c Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland
^d A.F. Ioffe Physical-Technical Institute, Russian Academy of Sciences 194021 St. Petersburg, Russia

Energy level positions of the nickel 2+/1+ and cobalt 2+/3+ charge states have been used to estimate band edges for the valence and conduction bands of ZnSe-based alloys with cation (ZnCdSe) and anion (ZnSSe) substitution. Chemical trends in band offsets of heterostructures of Zn- or Mn-based II-VI compounds are analysed. Further on, the change of Ni^{2+}(3d^8) and Co^{2+}(3d^7) intra-d shell transition bands upon the alloying of host material is discussed.
PACS numbers: 71.55.Gs, 78.20.Wc

PHOTOLUMINESCENCE OF Co-DOPED ZnCdSe AND ZnSSe ALLOYS

T.P. Surkova

Institute of Metal Physics, Ural Division of Russian Academy of Sciences 620219 Ekaterinburg GSP-170, Russia

H. Born, P. Thurian, A. Hoffmann, W. Busse, H.-E. Gumlich, I. Broser

Technical University Berlin, Institute of Solid State Physics, 10623 Berlin, Germany

and W. Giriat

IVIC, Centro de Fisica, Apto 1827, Caracas 1010A, Venezuela

Photoluminescence measurements have been carried out for \linebreak Zn_{1-x} Cd_x Se:Co and ZnS_xSe_{1-x}:Co mixed crystals. Changes of recombination channels are observed in mixed crystals as compared to the emission of host binary compounds. Character of changes is slightly different for the alloys with cation and anion substitution. Photoluminescence kinetics of the L-line and of two other Co^{2+} intra-shell emission bands was measured to determine radiative decay rates.
PACS numbers: 71.55.Gs, 78.20.Wc

EFFICIENT TWO-CENTER AUGER MECHANISM OF ELECTRON TRAPPING BY Fe^{3+} IONS IN ZnSe:Fe,Cr

M. Surma and M. Godlewski

Institute of Physics, Polish Academy Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

A detailed analysis of decay kinetics of light induced electron spin resonance signals of Cr^{1+} and Fe^{3+} ions in ZnSe:Fe,Cr is given. We observe that the Cr^{1+} electron spin resonance signal decays once free electrons are thermally ionized from shallow donors of ZnSe. Such unusual behavior of the Cr^{1+} electron spin resonance signal is explained by efficient two-center Auger recombination: the Cr^{1+} center is ionized due to the Auger-type energy transfer from the electron being trapped by the Fe^{3+} ion. Such process is shown to be consistent with the temperature dependence of the decay times of electron spin resonance signals. Its quantum efficiency is estimated to be as large as 18% for Cr and Fe concentrations which were studied.
PACS numbers: 71.55.Gs, 76.30.He, 78.55.Et

RAMAN CHARACTERIZATION OF MBE-GROWN LAYERED MnTe/CdTe STRUCTURES

W. Szuszkiewicz^a, M. Jouanne ^b, J.F. Morhange^b, M.A. Kanehisa^b, H. Mariette^c, J.M. Hartmann^c, E. Dynowska^a, G. Karczewski^a, T. Wojtowicz^a, J. Kossut^a and J. Barnas^d

^a Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland
^b Laboratoire des Milieux Desordonnes et Heterogenes, UPMC Case 86, 4 place Jussieu, 75252 Paris, Cedex 05, France
^c Equipe CEA-CNRS ``Microstructures de Semiconducteurs II-VI'' de l'Universite J. Fourier et CEA/DRFMC, BP 87, 38054 Grenoble, France ^dUnite Mixte de Physique CNRS-Thomson, Orsay, France

Raman scattering measurements on (MnTe)_8/(Cd_{0.64}Zn_{0.36}Te)_8 multilayer grown by MBE method and on various (MnTe)_n/(CdTe)_{12} multilayers (where n=8,12,16,24) were performed at low temperatures. In the \overline z(x,x)z polarization, structures corresponding to folded acoustic phonons were found. In \overline z(x,y)z polarization new complex structures were observed in the low-frequency part of Raman scattering spectra. A possible magnetic origin of these structures is discussed.
PACS numbers: 75.30.Ds, 75.70.Ak, 78.30.-j

TEMPERATURE DEPENDENCE OF RAMAN SCATTERING BY MAGNONS IN BULK-LIKE MBE-GROWN MnTe FILMS

W. Szuszkiewicz ^a, J.F. Mohrange^b, M. Jouanne^b, M.A. Kanehisa^b, R. Swirkowicz^c, E. Dynowska^a, E. Janik^a, T. Wojtowicz^a and J. Kossut^a

^a Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland
^b Laboratoire de Milieux Desordonnes et Heterog enes, UPMC Case 86, 4 place Jussieu, 75252 Paris Cedex 05, France ^c Warsaw Technical University, Koszykowa 75, 00-662 Warszawa, Poland

Temperature dependence of the magnon frequency was studied for cubic MnTe epilayers by the Raman scattering measurements. Experimental data are compared to the results of theoretical calculations performed within the framework of the Heisenberg model using Green's function formalism.
PACS numbers: 75.30.Ds, 75.50.Pp, 78.30.-j

SELECTED PROPERTIES OF LATTICE DYNAMICS OF HgSe AND \beta-HgS

W. Szuszkiewicz, K. Dybko, E. Dynowska, J. Gorecka, B. Witkowska

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland

B. Hennion

Laboratoire Leon Brillouin

M. Jouanne and C. Julien

Laboratoire des Milieux Desordonnes et Heterogenes, Universite Pierre et Marie Curie Case 86, 4, place Jussieu, 75252 Paris cedex 05, France

Optical phonon dispersion for \beta-HgS was measured by the neutron scattering for the first time. The results confirmed theoretically predicted anomalous behavior of phonon modes in this material, resulting probably from high ionicity of mercury sulphide and large difference of Hg and S atomic mass. Influence of the isotopic effects on the TO-phonon mode for HgSe and HgS is analyzed. The possible observation of such effects in IR reflectivity spectra taken for HgSe at low temperature is discussed.
PACS numbers: 61.12.-q, 63.20.-e, 78.30.-j

PHONON DEFORMATION POTENTIALS FROM RAMAN MEASUREMENTS ON SEMICONDUCTOR MEMBRANES

W. Trzeciakowski^{a,b}, J. Martinez-Pastor^b and G. Martinez-Criado ^b

^a High Pressure Research Center, Polish Academy of Sciences Sokolowska 29, 01-142 Warszawa, Poland
^b Departamento de Fisica Aplicada, Universidad de Valencia 46100 Burjassot (Valencia), Spain

It is shown that the phonon deformation potentials in semiconductors can be determined by Raman scattering on hydrostatically and biaxially deformed samples. The complete data includes biaxial deformation in the (100), (111), and (110) planes. Biaxial strain is applied to the sample using the recently developed membrane method. The phonon displacement under biaxial strain can be directly obtained from Raman measurements on a single membrane provided we determine the strain from the splitting of the band gap using e.g. the photoreflectance technique. Alternatively, the ratios of different phonon shifts can supply the necessary information. The method is illustrated with experimental results for GaP.
PACS numbers: 78.30.Fs, 78.20.Hp, 63.20.Ry

CALCULATION OF EXCITONIC ABSORPTION SPECTRUM OF GaAs QUANTUM WIRE FREE-STANDING IN VACUUM

P. Vagner^a, D. Munzar^b and M. Mosko^a

^a Institute of Electrical Engineering, Slovak Academy of Sciences Dubravska cesta 9, 842 39 Bratislava, Slovak Republic
^b Department of Solid State Physics, Faculty of Science Masaryk University, Kotlarska 2, 611 37, Czech Republic

The electron-hole interaction in a thin (\approx10 nm) GaAs quantum wire free-standing in vacuum is strongly enhanced by the image charge due to the abrupt permittivity drop at the wire surface. As a result, the exciton binding energies are much larger and the exciton wave functions much more localised than those of the GaAs quantum wire surrounded by the AlGaAs. The absorption spectrum of the free-standing wire shows besides the 1s exciton peak also the 3s and 5s exciton peaks, even if the peaks are 15 meV broad. The continuum absorption edge shows a large blue shift due to the renormalization of single-particle energies by the image charge.
PACS numbers: 73.20.-r, 73.20.Dx

PECULIARITIES OF SPACE-CHARGE-LIMITED PHOTOCURRENT

M. Vili\=unas, G. Juska, K. Arlauskas and V. Baltusis

Department of Solid State Electronics, Vilnius University Saul\.etekio 9, III build., 2054 Vilnius, Lithuania

We demonstrate new advantages of the space-charge-limited photocurrent technique for the investigations of charge carrier recombination. Bimolecular recombination coefficient in a-Si:H estimated according to suggested method for both electrons and holes is presented.
PACS numbers: 73.50.Fq, 73.50.Gr, 73.61.Jc

ELECTRONIC PROPERTIES AND DYNAMIC SUSCEPTIBILITY OF MnTe SYSTEMS

M. Wilczynski and R. Swirkowicz

Institute of Physics, Warsaw University of Technology Koszykowa 75, 00-662 Warsaw, Poland

Thin MnTe films are investigated. Electronic structure, local density of states and local magnetic moments are calculated for systems with ferromagnetic and antiferromagnetic order. Spin-dependent modifications of the density of states near the surface are results of the changes in p{-}d hybridization. Magnetic longitudinal and dielectric susceptibilities are calculated.
PACS numbers: 75.50.Pp, 75.70.-i, 75.10.Lp

OSCILLATING ANTIFERROMAGNETISM OF ULTRATHIN EuTe LAYERS

Z. Wilamowski

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland

G. Springholz, V. Svrcek and W. Jantsch

Johannes Kepler Universitat, 4040 Linz, Austria

We study magnetic resonance on EuTe/PbTe superlattices. Analysis of the magnetic dipole anisotropy in the superlattices and of the EPR amplitude of isolated Eu ions in the PbTe wells shows that the diffusion at interfaces is very small. The real thickness of EuTe can be evaluated with an accuracy better than one monolayer. Since for EuTe layers thicker than 2 monolayers there is no difference in the character of the antiferromagnetic resonance observed for even and odd numbers of monolayers, we conclude that there is no static magnetization of the antiferromagnetic sublattices. Nevertheless, long range antiferromagnetic order is clearly evident.
PACS numbers: 75.50.Ee, 75.50.Pp, 76.50.+g

LOCALIZED SPIN RELAXATION DUE TO COUPLING TO EFFECTIVE MASS STATES

Z. Wilamowski, J.E. Dmochowski

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

and W. Jantsch

Johannes Kepler Universit at, 4040 Linz, Austria

The EPR of residual Mn in CdF_2 doped with Y, In and Ga is investigated. Although these donors are barely seen in EPR, they manifest themselves by a new effect: a drastic resonant reduction in the longitudinal relaxation rate of Mn which occurs only if the Zeeman splitting of the two subsystems coincide. In this situation, the saturation of those of the six Mn hyperfine lines is weakened which coincide with the shallow donor resonance.
PACS numbers: 75.10.Jm, 75.50.-y

OPTICAL AND ELECTRICAL PROPERTIES OF HIGH TEMPERATURE ANNEALED HETEROEPITAXIAL GaN:Mg LAYERS

M. Wojdak, J.M. Baranowski, B. Suchanek, K. Pakula

Institute of Experimental Physics, Warsaw University Hoza 69, 00-681 Warszawa, Poland

J. Jun and T. Suski

High Pressure Research Centre, Polish Academy of Sciences Sokolowska 29/37, 01-142 Warszawa, Poland

In this paper we present for the first time luminescence and electrical measurements of GaN:Mg heteroepitaxial layers annealed at very high temperatures up to 1500^\circC and at high pressures of nitrogen up to 16 kbar. The presence of high nitrogen pressure prevents GaN from thermal decomposition. It was found that annealing in the presence of additional Mg atmosphere leads to a high quality p-type epitaxial layer of the hole concentration equal to 2\times10^{17} cm^{-3} and mobility 16 cm^2/(V s). However, annealing at high temperatures without additional magnesium causes conversion to n-type. It is also shown that in the high temperature annealed GaN:Mg epilayers the donor-acceptor luminescence is the dominant recombination channel.
PACS numbers: 78.66.Fd, 78.55.Cr, 73.61.Ey

NOVEL CdTe/CdMgTe GRADED QUANTUM WELL STRUCTURES

T. Wojtowicz, M. Kutrowski, G. Karczewski, G. Cywinski, M. Surma, J. Kossut

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

D.R. Yakovlev, W. Ossau, G. Landwehr

Physikalisches Institut der Universitat Wurzburg Am Hubland, 97074 Wurzburg, Germany

and V. Kochereshko

A.F. Ioffe Physico-Technical Institute, Russian Academy of Sciences St. Petersburg, Russia

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^-).
PACS numbers: 73.20.Dx, 78.55.Et

BAND MIXING EFFECTS IN QUANTUM WELL MAGNETOEXCITONS

R. Wysocki, W. Bardyszewski

Institute of Theoretical Physics, Warsaw University, Hoza 69, 00-681 Warsaw, Poland

S. Schoser and M. Potemski

Grenoble High Magnetic Field Laboratory, MPI/FKF and CNRS BP 166 Grenoble, Grenoble cedex 9, France

The influence of intersubband mixing in quantum wells of semiconductors with zinc-blende structure is studied both experimentally and theoretically. A multiband magnetoexciton model is described which takes into account k\cdot p mixing between valence subbands and the effective Coulomb interaction for an arbitrary confinement potential shape. Theoretical results reproduce very well the photoluminescence excitation spectra of GaAs/AlGaAs single quantum wells of various widths. In particular, the characteristic avoided crossing between the lowest light-hole exciton Landau level and excited heavy-hole exciton Landau level occurring at \sigma^- polarization is accurately described by our theory.
PACS numbers: 71.35.Ji, 71.70.Ej

CYCLOTRON-INTERSUBBAND COUPLING IN PERIODICALLY MODULATED QUASI-TWO-DIMENSIONAL ELECTRON GAS

M. Zaluzny and T. Stanko

Institute of Physics, M. Curie-Sklodowska University Pl. M. Curie-Sklodowskiej 1, 20-031 Lublin, Poland

The problem of the coupling between the Landau levels originating from the ground and first excited subband in laterally modulated quasi-two-dimensional systems in the presence of the tilted magnetic field is discussed in the framework of the one-electron perturbation theory. It was found that the tilting of the superlattice potential leads to the strong dependence of this coupling on the orientation of the magnetic field with respect to the lateral confinement direction.
PACS numbers: 73.20.Dx, 73.61.Ey

INVESTIGATION OF SPIN-GLASS TRANSITION IN SEMIMAGNETIC QUANTUM WELLS BASED ON Cd_{1-x}Mn_xTe BY MEANS OF OPTICAL SPECTROSCOPY

U. Zehnder, D.R. Yakovlev, W. Ossau, A. Waag, G. Landwehr

Physikalisches Institut der Universitat Wurzburg, 97074 Wurzburg, Germany

T. Wojtowicz, G. Karczewski and J. Kossut

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

The spin-glass transition in Cd_{1-x}Mn_xTe epitaxial layers and bulk samples with 0.24\le x\le0.43 and in quantum well structures on the basis of Cd_{1-x}Mn_xTe were investigated by means of optical spectroscopy. Reduction of dimensionality of Cd_{1-x}Mn_xTe layers down to the quasi-two-dimensional case realized in Cd_{1-x}Mn_xTe/Cd_{1- y}Mn_yTe 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_xTe quantum wells.
PACS numbers: 78.55.Et, 71.35.Ji

SUBSTRATE DEFECTS FILTRATION DURING EPITAXIAL LATERAL OVERGROWTH OF GaAs

Z.R. Zytkiewicz and D. Dobosz

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

Results on the growth of GaAs on (001) GaAs substrates by the epitaxial lateral overgrowth technique are reported. We show that the ratio of normal to lateral growth rates in the epitaxial lateral overgrowth process can be controlled by the crystallographic orientation of the seeds and by Si adding to the melt. Experimental data showing that the dislocations threading from the substrate are efficiently filtered and cannot propagate to the epitaxial lateral overgrowth layers are presented. These findings prove that the epitaxial lateral overgrowth process is the powerful method to grow epilayers with low dislocation density on high dislocation density substrates.
PACS numbers: 68.55.Ln

PHOTOINDUCED DEFECTS CREATION ON SULFUR PASSIVATED SURFACE OF GaAs

Z.R. Zytkiewicz^{a,b}, L. Dobaczewski^b, D. Gomez^a and F. Briones^a

^a Instituto de Microelectronica de Madrid Isaac Newton 8, 28760 Tres Cantos, Madrid, Spain
^b Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

We report on photoinduced defect creation on the sulfurized (100) GaAs surface. The process manifests itself by unrecoverable temporal decrease in the photoluminescence intensity of the GaAs surface treated by (NH_4)_2S_x solution. The results are discussed in terms of a photoinduced process of the As_{Ga} antisite generation on the sulfurized surface of GaAs.
PACS numbers: 68.35.Dv, 68.45.Da

ELECTROMAGNETIC PROPERTIES OF MESOSCOPIC CYLINDER

E. Zipper, M. Stebelski and M. Lisowski

Instytut Fizyki, Uniwersytet Slaski Uniwersytecka 4, 40-007 Katowice, Poland

The electromagnetic response of a mesoscopic cylinder made of a normal metal or a semiconductor is studied. The relation between the induced current J(\we q,w) and the electric field E(\we q,w) is derived. It is shown that the kernel K(\we q,w) which determines the properties of the system has a finite limit which implies infinite conductivity. The mesoscopic cylinder by virtue of its topology and small dimensions can support a persistent current. If the coherence of currents from different channels is strong enough a novel effect - the self-sustaining current can be obtained. We show that a mesoscopic multichannel system exhibits some features which bear resemblance to the superconductor.
PACS numbers: 71.30.+h, 72.10.-d

ANISOTROPIC LATTICE MISFIT RELAXATION IN AlGaAs SEMI-BULK LAYERS GROWN ON GaAs SUBSTRATES BY LIQUID PHASE ELECTROEPITAXY

Z.R. Zytkiewicz, J. Domagala, J. Bak-Misiuk, D. Dobosz

Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland

and M. Leszczynski

High Pressure Research Center, Polish Academy of Sciences Sokolowska 29/37, 01-142 Warsaw, Poland.

Experimental evidence for unidirectional microcracking in semi-bulk AlGaAs layers grown on (001) GaAs substrates is presented. The asymmetrical microcracking leads to anisotropic lattice misfit relaxation in the AlGaAs/GaAs structure and is explained in terms of higher mobility of [-110]-oriented \alpha-type dislocations than that of \beta-type dislocations oriented in [110] direction.
PACS numbers: 68.55.Ln, 68.60.Bs