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Vol. 92 No 4 October'97
PHYSICS OF NEUTRAL-TO-IONIC PHASE TRANSITION IN ORGANIC CHARGE TRANSFER
SEMICONDUCTING COMPOUNDS
H. Cailleau, M.H. Lemee-Cailleau, M. Le Cointe
Groupe Matiere
Condensee et Materiaux, UMR CNRS 6626 Universite de Rennes 1, 35042
Rennes cedex, France
and T. Luty
Institute of Physical and Theoretical Chemistry, Technical
University of Wroclaw Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
An uncommon excitonic instability takes place in some exotic
semiconducting compounds. Indeed, the equilibrium neutral-to-ionic (N-I)
phase transition, as well as the non-equilibrium photo-induced phase
transformation, observed in some organic charge-transfer complexes, originate
from intra- and inter-chain cooperative effects between structurally relaxed
charge-transfer excitations. This electronic-structural phase transition
manifests itself by a change of the degree of charge-transfer and a
dimerization distortion with the formation of donor-acceptor pairs along the
stacking axis in the I phase. Thermal charge-transfer excitations associated
with the formation of I strings along N chains are at the heart of the
mechanism of this phase transition. These relaxed electronic excitations,
which are an intrinsic feature of low-dimensional systems with strong
electron-phonon coupling, can be described in terms of self-trapping and
self-multiplication of charge-transfer excitons. Precise structural
studies on the prototype compound, tetrathiafulvalene-p-chloranil allow to
highlight the respective role taken by the ionicity and the dimerization.
Symmetry and thermodynamics analysis of the N-I transition, based on recent
determination of the pressure-temperature phase diagram, make possible to
present a consistent picture of this phase transition. Supported by
theoretical considerations taking into account the interplay between quantum
and thermal effects, the experimental observations show that the N-I
transition results from the condensation and the ordering (crystallization)
of charge-transfer excitations, following a phase diagram analogous to the
solid-liquid-gas one.
PACS numbers: 61.50.Ks, 71.35.Aa, 71.38.+i
RESONANT TUNNELLING STUDIES OF CHAOS IN QUANTISED SYSTEMS
L. Eaves, T.M. Fromhold, P.B. Wilkinson and F.W. Sheard
Department of
Physics, University of Nottingham, Nottingham NG7 2RD, UK
This paper gives a brief introductory overview of quantum chaology,
with particular reference to recent experimental work involving the use of
semiconductor heterostructures. In the presence of a tilted magnetic field, a
double-barrier resonant-tunnelling device incorporating a quantum well
produces a chaotic stadium for electron motion. The basic properties of this
system are described. It is shown how resonant magnetotunnelling spectroscopy
provides firm experimental evidence for the effect of scarred wave functions
on a physically-measurable property, in this case the measured
current-voltage characteristics of the device. The paper concludes with some
speculations concerning for the development of this field.
PACS numbers: 72.20.My,
73.40.Gk, 85.30.Mn, 05.45.+b
SKYRMIONS AND THE \nu=1 QUANTUM HALL FERROMAGNET
M.J. Manfra, B.B. Goldberg
Dept. of Physics, Boston University, Boston
MA 02215, USA
L. Pfeiffer and K. West
Bell Laboratories, Lucent Technologies, Murray
Hill, NJ 07974, USA
Recent experimental and theoretical investigations have resulted in a
shift in our understanding of the \nu=1 quantum Hall state. There now
exists a wealth of evidence that the excitation gap and the resulting
quasiparticle spectrum at \nu=1 are due {\em predominately} to the
ferromagnetic many-body exchange interaction. A great variety of
experimentally observed correlations at \nu= 1 {\em cannot} be incorporated
into a perturbative expansion around the single-particle model, a scheme long
thought to describe the integral quantum Hall effect at filling factor 1.
Theorists now refer to the \nu=1 state as the quantum Hall ferromagnet. In
this paper we review recent theoretical and experimental progress and detail
our own optical investigations of the \nu= 1 quantum Hall regime. The
technique of magneto-absorption spectroscopy has proven to be powerful a
probe of the occupancy of the lowest Landau level in the regime of
0.7<\nu<1.3 about the spin gap. Additionally, we have performed
simultaneous measurements of the absorption, photoluminescence and
photoluminescence excitation spectra of the \nu=1 state in order to
elucidate the role of excitonic and relaxation effects in optical
spectroscopy in the quantum Hall regime.
PACS numbers: 73.40.Hm, 78.66.-w, 73.20.Mf,
71.70.Gm, 73.20.Dx
QUANTUM DOTS - THEORY FOR EXPERIMENTS
L. Jacak^a, J. Krasnyj^b and A. Wojs^a
^a Institute of Physics,
Technical University of Wroclaw Wybrzeze Wyspianskiego 27, 50-370
Wroclaw, Poland
^b Institute of Mathematics, University of Opole, Oleska
48, 45-951 Opole, Poland
A simple model based on the effective-mass method and treating a
quantum dot as a small irregularity of the periodic crystal field is
developed and used for the description of the radiative recombination of an
exciton captured in that quasi-zero-dimensional structure. The additional
peaks appearing in the photoluminescence spectra at the critical quantum dot
size are predicted as a consequence of the metastable excited states
occurring in the energy spectrum of a confined exciton. The obtained
dependence of the photoluminescence spectrum on the dot size and magnetic
field reproduces well the available experimental results.
PACS numbers: 73.20.Dx,
71.35.Ji, 78.20.Ls
THEORY OF OPTICALLY NONLINEAR EFFECTS IN ULTRAFAST SPATIO-TEMPORAL
DYNAMICS OF SEMICONDUCTORS
A. Knorr, F. Steininger and S.W. Koch
Fachbereich Physik und Zentrum
fur Materialwissenschaften, Philipps-Universitat Renthof 5, 35032
Marburg, Germany
Ultrafast spatio-temporal effects in optically excited semiconductors
are investigated by solving the coupled semiconductor Maxwell-Bloch
equations which include the relevant relaxation phenomena. The analysis is
used to describe transport of electronic excitations on nano- to micrometer
scales with a dynamic range on the femto- to picosecond time
scale.
PACS numbers: 78.47.+p, 78.66.-w
EXAMPLES OF MICROSTRUCTURE-RELATED PROPERTIES OF GALLIUM NITRIDE
M. Leszczynski
High Pressure Research Center Unipress, Polish Academy
of Sciences Sokolowska 29/37, 01-142 Warsaw, Poland
The work provides a brief overview and the latest experimental results
concerning the microstructure of gallium nitride. Because of the importance
for the optoelectronic and electronic technologies, mainly problems related
to the lattice mismatch between substrates and GaN layers are discussed.
Three main substrates, sapphire, silicon carbide and high-pressure-grown bulk
GaN crystals, are compared. Mosaicity, thermal strains and surface
roughnesses of the GaN layers grown on those substrates are reported. The
application of high-pressure technologies makes it possible to use
temperatures higher by a few hundred degrees with respect to the atmospheric
pressure for which the decomposition of gallium nitride occurs at
temperatures below 1000^\circC. Annealing at pressures higher than 10 kbar
and temperatures up to 1550^\circ C causes modifications of the
microstructure of GaN heteroepitaxial layers on sapphire. For example, their
mosaicity decreases as observed by narrowing of the X-ray diffraction peaks.
The implanted layers recover upon high-pressure annealing and give a strong
dopant-related luminescence.
PACS numbers: 61.72.Ji, 61.72.Vv
IV-VI SEMIMAGNETIC SEMICONDUCTORS WITH RARE EARTH IONS
T. Story
Institute of Physics, Polish Academy of Sciences Al. Lotnik/ow
32/46, 02-668 Warsaw, Poland
The electronic and magnetic properties as well as the applications of
IV-VI semiconductors with rare earth ions of Eu and Yb are briefly
discussed. The detailed analysis is presented of the recent experimental
investigations of the magnetic and transport properties of IV-VI
semimagnetic crystals with Gd. It concerns, in particular, the effect of
Fermi level position controlled f{-}f exchange interaction between Gd ions
in Sn_{1-x}Gd_xTe.
PACS numbers: 75.20.Ck, 75.30.Et
USE OF BISTABLE CENTERS IN CdF_2 FOR HOLOGRAPHIC RECORDING
J.M. Langer, B. Koziarska-Glinka and A. Suchocki
Institute of Physics,
Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland
It is shown that metastable centers in various semiconductors can be
used for efficient hologram recording. This type of holographic materials has
a very high dynamic range and sensitivity. Their major drawback for possible
applications is low metastability temperature. This problem can be overcome
by using CdF _2:Ga crystals, which exhibit metastability below 240 K. This
material is suitable for writing thick and multiple holograms both in static
and dynamic regimes.
PACS numbers: 42.40.Lx, 42.40.Ht, 78.20.Ci
RAMAN SCATTERING PHOTONIC AND POLARITONIC RESONANCES IN SEMICONDUCTOR
MICROCAVITIES
B. Jusserand and A. Fainstein
CNET/Laboratoire de Bagneux, BP107,
92225 Bagneux Cedex, France
Single and double optical resonant Raman scattering is demonstrated in
semiconductor microcavities. Its evolution towards excitonic ingoing
resonance relies on cavity-polaritons as intermediated steps of the inelastic
scattering. Implications for high-sensitivity spectroscopy and low-power
stimulated processes are emphasized.
PACS numbers: 63.20.-e, 82.80.Ch
TWO-ELECTRON QUANTUM DOTS IN MAGNETIC FIELD
J. Adamowski and B. Spisak
Faculty of Physics and Nuclear Techniques,
Technical University (AGH) Al. Mickiewicza 30, 30-059 Krakow, Poland
A theoretical description is given for electronic properties of
semiconductor quantum dots in a magnetic field. A two-electron model is
applied for electrons in a cylindrical quantum dot with a parabolic
confinement potential. The eigenvalue problem is solved by the variational
method with the trial wave function proposed in the form of linear
combination of S-type and P-type Gaussians. The energy levels of singlet
and triplet states with arbitrary radial and magnetic quantum numbers have
been calculated as a function of the applied magnetic field. The calculated
cyclotron transition energies agree well with those measured for InGaAs/GaAs
quantum dots. It is shown that the electron-electron interaction has a small
influence on the transition energy.
PACS numbers: 73.20.Dx
FIR MAGNETOOPTICAL MEASUREMENTS ON MOCVD GROWN InAs
T. Andrearczyk, K. Karpierz, R. Bozek, R. Stepniewski and M.
Grynberg
Institute of Experimental Physics, Warsaw University, Hoza 69,
00-681 Warsaw, Poland
In this paper we report results of magnetooptical measurements done on
standard InAs MOCVD layers grown on GaAs. Extremely narrow lines (half-widths
of the order of 20 mT) - narrower than found by other authors in high
quality MBE InAs epilayers on GaAs - as well as the lines of typical
half-widths have been found both in the photoconductivity spectra and in the
transmission spectra. A detailed comparison with the theoretical dependence
of shallow donor and Landau level energies on magnetic field leads to the
conclusion that they originate from cyclotron resonance and impurity-shifted
cyclotron resonance transitions in that material.
PACS numbers: 72.40.+w, 71.55.-i,
78.30.-m
COHERENT AND SEQUENTIAL TUNNELING IN HIGH MAGNETIC FIELD
A.E. Belyaev, S.A. Vitusevich
Institute of Semiconductor Physics,
National Academy of Sciences of Ukraine Prospekt Nauki 45, 252028 Kiev,
Ukraine
D. Maude and J.C. Portal
Service National des Champs Intenses Centre
National de la Recherche Scientifique, 38042 Grenoble, France
In the resonant tunneling diode incorporating a wide one-sided spacer
layer, an oscillation picture has been studied in both polarities of the
applied voltage in high magnetic field. The results lead to the conclusion
that the interference between the electron waves running in the forward
direction and the ones reflected at some potential step can occur in both the
emitter and collector regions. The characteristic lengths corresponding to
the path of the ballistic motion of electrons were estimated. An exchange
enhancement of the electronic g-factor in two-dimensional systems was
observed.
PACS numbers: 73.40.Gk, 85.30.Mn
DYNAMICS OF HOT ELECTRONS IN ZnSe-ZnTe DOUBLE BARRIER HETEROSTRUCTURES
P. Bala
Institute of Physics, N. Copernicus University, Grudziadzka
5, 87-100 Torun, Poland
In this paper we perform a detailed study of the transport of hot
electrons in the double barrier heterostructures with the presence of a
collector barrier. This system is considered as a double barrier resonant
tunneling device. The electron is described by time-dependent Schrodinger
equation, which allows us to study detailed dynamics of the carriers. The
influence of an energy step in the collector area of the device on the
tunneling probability is investigated. The significant role of dissipation
due to electron-phonon interactions is presented.
PACS numbers: 03.65.-w, 73.40.Gk,
73.61.-r
SUBSTRATE-INDUCED STRAIN IN EPITAXIAL LEAD CHALCOGENIDES BY
GALVANOMAGNETIC EFFECT ROTATIONAL DEPENDENCE
N.N. Berchenko, O.A. Dobriansky, A.V. Korovin, A.Yu. Nikiforov, V.S.
Yakovyna
``Lviv Polytechnic'' State University, 12 Bandera St, 290646 Lviv,
Ukraine
and H. Zogg
AFIF at Swiss Federal Institute of Technology, Technopark
ETH-Teil 8005 Zurich, Switzerland
On the example of the PbTe and Pb_{0.77} Sn_{0.23}Te on BaF_2 the
possibility of using the weak magnetic field resistance technique for the
evaluation of mismatch-thermally induced strains in semiconductors with
multivalley band structure is discussed.
PACS numbers: 72.20.My, 72.80.Jc
CORRELATIONS IN MAGNETIC-NONMAGNETIC SEMICONDUCTOR SUPERLATTICES -
SIMPLE MODEL
J. Blinowski
Institute of Theoretical Physics, Warsaw University Hoza
69, 00-681 Warszawa, Poland
and P. Kacman
Institute of Physics, Polish Academy of Sciences Al.
Lotnikow 32/46, 02-668 Warszawa, Poland
The magnetic interactions in superlattices formed by alternating layers
of magnetic and nonmagnetic semiconductors with common anions were studied
theoretically. Within a one-dimensional tight-binding model by minimising the
total electronic energy we show the existence of an efficient long range
mechanism of magnetic correlations between the neighbouring magnetic layers
in such superlattices. The cases of magnetic ions in the barriers
(e.g., EuTe/PbTe) and in the wells, with the order within the magnetic
layers being either ferromagnetic or antiferromagnetic, have been considered
and compared with the paramagnetic case. In the case of antiferromagnetic
ordering within magnetic layers we have found that for even and odd numbers
of magnetic monolayers different magnetic superlattices are energetically
favourable.
PACS numbers: 75.70.Ak, 75.25.+z
SINGLE TEMPERATURE SCAN DETERMINATION OF DEFECT PARAMETERS IN DLTS
EXPERIMENT
L. Dobaczewski^a, Z. Kancleris^b, K. Bonde Nielsen^c and A.R.
Peaker^d
^a Institute of Physics, Polish Academy of Sciences Al.
Lotnikow 32/46, 02-668 Warsaw, Poland
^b Semiconductor Physics Institute,
Vilnius, Lithuania
^c Institute of Physics and Astronomy, University of
Aarhus, Aarhus, Denmark
^d Centre for Electronic Materials, University of
Manchester Institute of Science and Technology, Manchester, UK
Many point and extended defects in silicon, and other semiconducting
materials, have been relatively well characterised by the standard DLTS
technique. In this method the activation energy of carrier emission from the
defect is calculated after multiple temperature scans. In this paper we
demonstrate a new approach to the technique, in which after a single
temperature scan the complete Arrhenius plot can be constructed for defects
present in the sample with considerable concentrations. This method is much
faster, accurate, and offers a much higher resolution in comparison with the
standard DLTS method.
PACS numbers: 68.55.Ln, 71.55.Cn, 73.40.Lq
TRANSPORT PROPERTIES OF SILICON \delta-DOPED GaAs IN HIGH ELECTRON
DENSITY REGIME
A.V. Buyanov, P.O. Holtz, G. Pozina, B. Monemar
Department of Physics
and Measurements Technology, Linkoping University 581 83, Linkoping,
Sweden
J. Thordson and T.G. Andersson
Department of Physics, Chalmers
University of Technology and Goteborg University 412 96, Goteborg,
Sweden
We report results for Si layers embedded in GaAs, extending from the
delta-doped (\delta-doped) range up to 6 monolayers derived by means of
variable temperature resistivity and Hall effect measurements, secondary ion
mass spectrometry and high resolution X-ray diffractometry techniques. The
conductivity transition from free carrier transport in ordered
\delta-layers (<1 ML) to strongly-localized two-dimensional variable
range hopping transport under potential fluctuation disordered conditions
(>4 ML) is clearly observed. This observation is in good agreement with the
secondary ion mass spectrometry and high resolution X-ray diffractometry
data. Results from the intermediate case with 2-3 MLs are also
discussed.
PACS numbers: 61.72.Vv, 68.55.Ln, 72.60.+g
FAR-INFRARED NARROW-BAND PHOTODETECTOR BASED ON MAGNETICALLY TUNABLE
CYCLOTRON RESONANCE-ASSISTED TRANSITIONS IN PURE n-TYPE InSb
L.H. Dmowski^a, M. Cheremisin^b, C. Skierbiszewski^a and W.
Knap^b
^a High Pressure Research Center, Polish Academy of Sciences
Sokolowska 29/37, 01-142 Warszawa, Poland
^b G.E.S. Universite
Montpellier II, Pl. Eugene Bataillon, 34060 Montpellier, France
We present the possibility of using magnetic field to enhance
responsivity and to tune spectral range of far-infrared InSb detector (based
on photoconductivity effect) beyond its standard range limited to about
30 cm^{-1}. We show that due to cyclotron resonance assisted transitions we
can use it as a tunable detector working up to energies about 180 cm^{-1}
(22 meV). We have used such a detector as a spectrometer for measurements of
the Landau emission from GaAs emitter.
PACS numbers: 72.40.+w, 78.20.Ls, 78.90.+t
SOME OPTICAL AND EPR PROPERTIES OF STRAIN-FREE GaN CRYSTALS OBTAINED BY
AMMONO METHOD
R. Dwilinski, J.M. Baranowski, M. Kaminska
Institute of Experimental
Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland
R. Doradzinski
Institute of Theoretical Physics, Warsaw University,
Hoza 69, 00-681 Warsaw, Poland
J. Garczynski, L. Sierzputowski
Dept. of Chemistry, Warsaw Univ. of
Technology Noakowskiego 4, 00-661 Warsaw, Poland
and M. Palczewska
Institute of Electronic Materials Technology,
Wolczynska 133, 01-919 Warsaw, Poland
AMMONO GaN is grown spontaneously from ammonia solution in form of
regular, well shaped, few micrometer crystals. Photoluminescence spectra of
these crystals are characterized by fixed positions of very narrow exciton
lines (FWHM down to 1 meV), where free excitons A, B, C, resolved two donor
bound excitons and acceptor bound exciton are visible. Fixed position of
exciton lines is in contrast to small changes of line energies which have
been always observed for epitaxial GaN layers because of strain present in
them. Free electron concentration of AMMONO GaN is less than few times
10^{15} cm^{-3}, as estimated from EPR signal of shallow donor. The
above-mentioned facts qualified these crystals as state of the art
strain-free, model material for basic parameter measurements of GaN. In this
work, results of PL and EPR measurements performed on AMMONO GaN crystals are
presented and discussed.
PACS numbers: 81.10.Dn
TWO-ELECTRON TRANSITION IN HOMOEPITAXIAL GaN LAYERS
A. Fiorek, J.M. Baranowski, A. Wysmolek, K. Pakula, M.
Wojdak
Institute of Experimental Physics, Warsaw University Hoza 69, 00-681
Warsaw, Poland
I. Grzegory and S. Porowski
High Pressure Research Center, Polish
Academy of Sciences Sokolowska 29, 01-142 Warsaw, Poland
It is shown that the luminescence mapping is a powerful method to help
identify optical transitions. Two-electron transition was identified in the
homoepitaxial GaN layer by this technique. It was found that the donor and
acceptor bound exciton emissions are spatially displaced and show intensity
maxima at different places of the epitaxial layer. It was also found that the
3.45 eV line, suspected as ``two-electron transition'', follows exactly the
donor bound exciton spatial distribution. Donor bound exciton recombines
leaving the neutral donor in the excited 2s state. Thus, 1s{-}2s
excitation being equal to 22 meV corresponds to 29 meV hydrogenic donor
binding energy. This is the first identification of the two-electron
transition in GaN.
PACS numbers: 78.66.Fd, 78.55.Cr
OBSERVATION OF THE COULOMB BLOCKADE AT 77 K IN A LATTICE-MISMATCHED
GaAs/Si HETEROJUNCTION
T. Figielski, T. Wosinski, A. Makosa
Institute of Physics, Polish
Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland
and F. Riesz
Research Institute for Technical Physics, Hungarian
Academy of Sciences P.O. Box 76, 1325 Budapest, Hungary
We investigated current-voltage characteristics of a
lattice-mismatched GaAs(n)/Si(p) heterojunction. For low bias voltages
at 77 K it exhibits a behaviour characteristic of the Coulomb blockade. We
discuss why this unexpected phenomenon can occur in the investigated
structures.
PACS numbers: 73.40.Gk, 73.40.Kp, 61.72.Lk
PHOTOACOUSTIC INVESTIGATION OF ABSORPTION EDGE OF Cd_{1-x}Mg_xSe
MIXED CRYSTALS
F. Firszt^a, S. Legowski^a, H. Meczynska^a, B. Sekulska^a,
J. Szatkowski^a, J. Zakrzewski^a and W. Paszkowicz^b
^a Institute of Physics, N. Copernicus University, Grudziadzka 5/7, 87-100 Torun, Poland
^b Institute of Physics, Polish Academy of Sciences Al. Lotnikow 32/46,
02-668 Warsaw, Poland
The Cd_{1-x}Mg_xSe crystals were grown by modified Bridgman method
for x ranging from 0 to 0.44. The photoacoustic spectroscopy was employed
for evaluation of the band gaps of series Cd_{1-x}Mg_xSe mixed crystals
with different composition. The photoacoustic spectra were measured at 300 K
and 90 K using continuous wave excitation in the range from 400 nm to 800 nm.
The increase in the band-gap energy with increasing Mg content is observed.
The photoacoustic results are compared with photoluminescence and
transmission spectra.
PACS numbers: 62.65.+k, 78.20.Hp, 78.55.Et
INFRARED ABSORPTION IN Si-Si_{1-x}Ge_x-Si QUANTUM WELLS
G. Fishman
Laboratoire de Spectrometrie Physique, UMR 5588, UJF
Grenoble 1-CNRS, BP87 38402 Saint Martin d'Heres Cedex, France
and R. Oszwaldowski
Institute of Physics UMK, Grudziadzka 5, 87-100
Torun, Poland
We use the eight-band \we k\cdot\we p model to describe the infrared
inter-subband absorption in Si-Si_{1-x}Ge_x-Si quantum wells, which
takes explicitly into account the \Gammap'_{25}(\Gammap_8^++\Gammap_7^+ in
the double group) valence band and the second conduction band
\Gammap'_2(\Gammap_7^-). We then obtain an accurate description of mixing
of the S wave function with the valence band functions.
PACS numbers: 73.20.Dx, 78.66.-w,
85.30.Vw
RECOMBINATION PROCESSES IN DOPED CdTe/CdMnTe MULTIPLE QUANTUM WELL
STRUCTURES GROWN BY MOLECULAR BEAM EPITAXY
M. Godlewski, T. Wojtowicz, G. Karczewski, J. Kossut
Institute of
Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw,
Poland
J.P. Bergman and B. Monemar
Department of Physics and Measurement
Technology, Linkoping University 581 83 Linkoping, Sweden}
An influence of doping level on exciton properties in n-doped
multiple quantum well structures of CdTe/CdMnTe is studied for multiple
quantum well structures prepared in the way that donor (indium) concentration
changes within the length of the sample. We show that the formation scenario
for neutral donor bound excitons in low-dimensional structures can be
different from that observed in bulk samples. We further show that in the
case of such quantum well structures we can selectively excite either
photoluminescence emission of localized or donor bound excitons, which is a
consequence of surprisingly weak energy transfer link between two types of
excitonic transitions.
PACS numbers: 78.47.+p, 78.55.Et
EXCITON TRANSFER IN MULTIPLE QUANTUM WELL STRUCTURES OF CdTe/CdMnTe
GROWN BY MOLECULAR BEAM EPITAXY
M. Godlewski, M. Surma, Z. Wilamowski, T. Wojtowicz, G. Karczewski, J.
Kossut
Institute of Physics, Polish Academy of Sciences Al. Lotnikow
32/46, 02-668 Warsaw, Poland
P.O. Holtz, J.P. Bergman and B. Monemar
Department of Physics and
Measurement Technology, Linkoping University 581 83 Linkoping, Sweden
The direct evidence for the efficient transfer of excitons from 4 nm
and 6 nm to 10 nm wide CdTe quantum wells is presented based on the results
of photoluminescence and photoluminescence excitation investigation.
Efficient transfer is observed for quantum wells separated by thick (50 nm)
CdMnTe barriers containing 10% or 30% Mn fraction. A new mechanism of the
transfer is proposed, which involves long range dynamic magnetic interactions
between free/bound excitons and Mn ions in the CdMnTe barrier regions of the
structure.
PACS numbers: 78.47.+p, 78.55.Et
HOT PHOTOLUMINESCENCE IN CdTe/CdMnTe QUANTUM WELL STRUCTURES GROWN BY
MOLECULAR BEAM EPITAXY
M. Godlewski, T. Wojtowicz, G. Karczewski, J. Kossut
Institute of
Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warsaw,
Poland
J.P. Bergman, P.O. Holtz and B. Monemar
Department of Physics and
Measurement Technology, Linkoping University 581 83 Linkoping, Sweden
A step-like emission is observed for CdTe/CdMnTe structures
\delta-doped with In. The new photoluminescence cannot be explained by
neither the Raman process nor by the ``ordinary'' hot photoluminescence. We
propose that magnetic interactions are responsible for the new
photoluminescence appearing due to a dramatic increase in a thermalization
time of hot excitons.
PACS numbers: 78.47.+p, 78.55.Et
ENHANCED EXCITON-PHONON INTERACTION IN STRAINED ZnCdSe/ZnSe QUANTUM
WELL STRUCTURES
M. Godlewski
Institute of Physics, Polish Academy of Sciences Al.
Lotnikow 32/46, 02-668 Warsaw, Poland
K. Leonardi and D. Hommel
Institute of Solid State Physics, Bremen
University, 28334 Bremen, Germany
Radiative recombination processes in pseudomorphic ZnCdSe/ZnSe
structures are compared to those observed in strain-relaxed structures grown
on GaAs substrates with thick ZnSe buffer layers. From the temperature
dependence of the photoluminescence line width we evaluate the strength of
exciton-phonon interaction with acoustic (dominant at lower temperatures)
and optical phonons. Stronger exciton-phonon interaction is observed for
pseudomorphic structures. Such enhanced exciton-phonon interaction is likely
responsible for a faster photoluminescence deactivation at increased
temperatures. We also report different exciton properties (photoluminescence
intensity, width, strength of exciton-phonon interaction) in quantum well of
a given width but in structures grown with different order of quantum wells.
More stable photoluminescence (with increasing temperature) is observed for a
given quantum well if it is closer to the buffer layer and not to the cap
layer.
PACS numbers: 68.60.-p, 76.70.Hb
EXCHANGE PARAMETERS OF CdCrS SEMIMAGNETIC SEMICONDUCTOR
M. Herbich, W. Mac, A. Twardowski
Institute of Experimental Physics,
Warsaw University Hoza 69, 00-681 Warsaw, Poland
K. Ando
Electrotechnical Laboratory, Tsukuba Science City, Ibaraki,
Japan
and M. Demianiuk
Institute of Technical Physics, Military Academy of
Technology Kaliskiego 2, 00-908 Warsaw, Poland
Free exciton magnetoreflectance and magnetization of Cd_{1-x}Cr_xS
(0.0024<0.0031) were measured at T=2.0 K and magnetic field up to 5 T.
Combining the heavy hole exciton splitting with the magnetization data the
exchange integral N_0\beta=+0.46\pm0.04 eV was evaluated within the
framework of mean field approximation.
PACS numbers: 71.70.Gm, 78.20.Ls, 78.30.Fs
PHOTOLUMINESCENCE STUDIES OF CUBIC PHASE GaN GROWN BY MOLECULAR BEAM
EPITAXY ON (001) SILICON COVERED WITH SiC LAYER
M. Godlewski, V.Yu. Ivanov
Institute of Physics, Polish Academy of
Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland
J.P. Bergman, B. Monemar
Dept. Phys. and Meas. Technology, Linkoping
University, 581 83 Linkoping, Sweden
A. Barski and R. Langer
CEA/Grenoble, DRFMC/SP2M, 17 r. des Martyrs,
38054 Grenoble, France
In this work we evaluate optical properties of cubic phase GaN
epilayers grown on top of (001) silicon substrate prepared by a new process.
Prior to the growth Si substrate was annealed at 1300-1400^\circC in
propane. The so-prepared substrate is covered with a thin (\approx4 nm) SiC
wafer, which allowed a successful growth of good morphological quality cubic
phase GaN epilayers. The present results confirm recent suggestion on smaller
ionization energies of acceptors in cubic phase GaN epilayers.
PACS numbers: 71.55.Eq,
78.47.+p
NONRADIATIVE RECOMBINATION PROCESSES IN (CdTe,CdCrTe)/CdMgTe QUANTUM
WELL STRUCTURES
J.P. Bergman and B. Monemar
Department of Physics and Measurement
Technology, Linkoping University 581 83 Link oping, Sweden
Photoluminescence transitions in (CdTe,CdCrTe)/CdMgTe structure grown
by molecular beam epitaxy are studied. Photoluminescence investigations show
a very strong reduction of the photoluminescence intensity from chromium
doped quantum wells. We explain this fact by a very efficient nonradiative
recombination in the chromium-doped quantum wells. The present results
indicate that the Auger-type energy transfer from excitons to chromium ions
is responsible for the photoluminescence deactivation. The efficiency of this
process is evaluated.
PACS numbers: 68.60.-p, 76.70.Hb
CALCULATIONS OF POINT DEFECTS IN AlN AND GaN; LATTICE RELAXATION EFFECTS
I. Gorczyca
High Pressure Research Center PAN, Sokolowska 29, 01-142
Warsaw, Poland
N.E. Christensen and A. Svane
Institute of Physics and Astronomy,
University of Aarhus, 8000 Aarhus C, Denmark
Native defects (vacancies, antisites and interstitials) and
substitutional impurities (Mg, Zn, and C) in cubic GaN and AlN are studied by
means of {\em ab initiotheoretical} calculations. We examine the energetic
positions of the defect levels and lattice relaxations effects. Whereas small
relaxations are found in the case of vacancies, the calculations predict that
large atomic displacements are associated with antisites. We also discuss the
metastable behavior of the nitrogen antisite.
PACS numbers: 73.61.Ey, 71.55.Eq
EFFECTS OF BALLISTIC TRANSPORT IN WIRES OF n-PbTe
G. Grabecki, J. Wrobel, T. Dietl
Institute of Physics, Polish Academy
of Sciences Al. Lotnikow 32/46, 02-668 Warszawa, Poland
E. Papis, E. Kaminska, A. Piotrowska
Institute of Electron Technology,
Al. Lotnikow 32/46, 02-668 Warszawa, Poland
Y. Ueta, G. Sprinholtz and G. Bauer
Institut fur Halbleiterphysik,
Johannes Kepler Universitat Linz, 4040 Linz, Austria
We present results of magnetotransport studies on quantum wires of
submicron PbTe epilayers, fabricated by means of electron beam lithography
and dry etching. When the wire width is reduced down to 1 \mum, the
transition from diffusive to ballistic regime is observed. Effects associated
with collimation and boundary scattering are found in the Hall, longitudinal,
and van der Pauw magnetoresistance for wires and junctions in the shape of a
cross.
PACS numbers: 73.23.Ad, 73.61.-r, 73.50.Dn
Cd_{1-x}Fe_xTe TERNARY CRYSTAL FORMATION STUDIED BY RESONANT
PHOTOEMISSION
E. Guziewicz, B.J. Kowalski, Z. Golacki, B.A. Orlowski
Institute of
Physics, Polish Academy of Sciences Al. Lotnikow 32/46, 02-668 Warszawa,
Poland
R.L. Johnson
Universitat Hamburg, II Institut fur
Experimentalphysik Luruper Chaussee 149, 22761 Hamburg, Germany
and J. Masek
Institute of Physics, Czech Academy of Sciences 180 40
Praha 8, Czech Republic
A resonant photoemission was used to study the ternary crystal
formation, when small amount of Fe atoms was deposited (in one monolayer
range of thickness) on the clean CdTe(100) surface. The constant initial
state spectra taken near the Fe 3p{-}3d transition after Fe deposition and
then again after heating process show the existence of two Fano-like
resonance. The differences of the energy distribution curves taken for both
resonance and antiresonance, respectively, allow us to distinguish two kind
of Fe 3d contributions to the valence band: one derived from the metallic
Fe islands on the surface and the second - derived from the Fe atoms built
into the Cd_{1-x}Fe_xTe crystal.
PACS numbers: 79.60.-i, 68.35.Fx
MAGNETIZATION STEPS IN Cd_{1-x}Mn_xTe OBSERVED IN COHERENT TRANSPORT
J. Jaroszynski, T. Dietl, J. Wrobel, G. Karczewski, T. Wojtowicz,
J. Kossut
Institute of Physics, Polish Academy of Sciences Al. Lotnikow
32/46, 02-668 Warszawa, Poland
D.K. Maude, P. van der Linden and J.C. Portal
Grenoble High Magnetic
Field Laboratory, MPI-FKF and CNRS, BP 166, 38042 Grenoble Cedex 09, France
Magnetoconductance measurements on submicron wires of
n^+-Cd_{1-x}Mn_xTe 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.
PACS numbers: 72.15.Rn, 73.20.Fz, 73.61.Ga
ANALYSIS OF RESONANT TUNNELING FOR CdTe-CdMgTe STRUCTURES
E. Kaczmarek
Institute of Physics, Polish Academy of Sciences Al.
Lotnikow 32/46, 02-668 Warszawa, Poland
In this paper we present model calculations of the current-voltage
characteristics for the CdTe/CdMgTe double barrier structures based on the
assumption that the electron effective masses in the barrier and well regions
of double barrier structure are different. The main features of the measured
I{-}V characteristics, i.e., the small current peak at low bias and much
larger peak at high voltage, are reproduced quite well by the calculated
curve. The results of magnetotunneling experiments can be also understood in
the frame of the proposed model.
PACS numbers: 73.40.Gk
PHONON CONFINEMENT AND ELECTRON CAPTURE TIME IN QUANTUM WELL
K. Kalna
Institute of Electrical Engineering, Slovak Academy of
Sciences Dubravska cesta 9, 842 39 Bratislava, Slovakia
The electron capture time via an electron-polar optical phonon
interaction is calculated considering the confinement of a phonon in a GaAs
quantum well laser structure. The effect of the phonon confinement decreases
the electron capture time about twice comparing the electron capture time
obtained from the interaction of an electron with the bulk phonon.
PACS numbers: 73.20.Dx,
73.61.Ey, 72.15.Nj
QUASIPARTICLE FORMATION AND DECAY IN PULSED PHOTOEXCITATION OF DISORDERED
SEMICONDUCTORS
A. Kalvova^a and B. Velicky^{a,b}
^a Inst. of Phys., Czech
Academy of Sciences Na Slovance 2, 180 40 Praha 8, Czech Republic
^b Faculty of Math. and Phys., Charles University Ke Karlovu 5, 121 16 Praha 2,
Czech Republic
The quasiparticle states in strongly illuminated semiconductors are
light hybridized electron and hole states, {\em Galickii quasiparticles}.
Their properties, especially if they are photoexcited at small detunings, may
be rather complex. A protracted formation period is followed by quantum beats
of two decaying resonances corresponding to both sides of the hybridization
gap. On an example of elastic scattering on an alloy disorder, these
phenomena are demonstrated and analyzed in terms of poles of the retarded
Green function and the corresponding residuals.
PACS numbers: 71.55.Eq, 72.10.Bg,
78.47.+p
MAGNETIC FIELD INFLUENCE ON AUGER EFFECT ON SHALLOW DONORS IN CdF_2
:Mn^{2+} LUMINESCENCE
A. Kaminska and A. Suchocki
Institute of Physics, Polish Academy of
Sciences Al. Lotnikow 32/46, 02-668 Warsaw, Poland
Direct observation of the suppression of the Auger effect on shallow
donors by the magnetic field in the luminescence of manganese ions in
semiconducting CdF_2 :Mn crystals is presented. The magnetic field
decreases the probability of the Auger effect, which is spin-dependent energy
transfer from the manganese ions to the electrons occupying shallow donors.
This results in the increase in the decay times of the
luminescence.
PACS numbers: 73.20.Hb, 73.50.Gr
OHMIC CONTACTS TO GaN BY SOLID-PHASE REGROWTH
E. Kaminska, A. Piotrowska, A. Barcz, L. Ilka, M. Guziewicz,
S. Kasjaniuk
Institute of Electron Technology, Al. Lotnikow 32/46, 02-668
Warszawa, Poland
E. Dynowska
Institute of Physics, Polish Academy of Sciences Al.
Lotnikow 32/46, 02-668 Warszawa, Poland
S. Kwiatkowski
Soltan Institute for Nuclear Studies, Hoza 69, 00-681
Warszawa, Poland
M.D. Bremser and R.F. Davis
Materials Science and Engineering, North
Carolina State University NC 27695-7907, USA
Ni/Si-based contact schemes based on the solid-phase regrowth process
have been developed to form low-resistance ohmic contacts to GaN with a
minimum contact resistivity of 1\times10^{-3} \Omega cm^2 and
\approx1\times10^{-2} \Omega cm^2 to GaN:Si
(n\approx2\times10^{17} cm^{-3}) and GaN:Mg (p\approx3\times10
^{17} cm^{-3}). The solid-phase regrowth process responsible for the ohmic
contact formation was studied using X-ray diffraction, secondary ion mass
spectrometry and Rutherford backscattering spectrometry.
PACS numbers: 73.40.Cg, 73.40.Ns
THEORETICAL AND EXPERIMENTAL STUDY OF THE RADIATIVE DECAY PROCESS IN A
MODULATION DOPED GaAs/AlGaAs HETEROINTERFACE
T. Lundstrom, J.P. Bergman, P.O. Holtz, B. Monemar
Department of
Physics and Measurement Technology, Linkoping University 581 83
Linkoping, Sweden
K. Campman, J.L. Merz and A.C. Gossard
QUEST Center, University of
California at Santa Barbara Santa Barbara, CA 93106, USA
We have theoretically and experimentally investigated the radiative
recombination process in an n-type modulation doped
GaAs/Al_{0.35}Ga_{0.65}As heterostructure. The dynamical reshaping of
the potential profile across the heterojunction, and the decay of the
spatially indirect radiative recombination between electrons in the
two-dimensional electron gas and photo-created holes, have been numerically
simulated for various values of the electric field across the heterojunction.
Optical matrix elements were deduced from a self-consistent solution of the
coupled Schrodinger and Poisson equations at every discrete point of time.
The calculated recombination energies and integrated luminescence intensities
were compared with experimental data from time-resolved photoluminescence
measurements on an 800 \AA wide GaAs/ AlGaAs heterostructure.
PACS numbers: 78.66.-w,
78.60.-b
HIGH MOBILITY 2D ELECTRON GAS IN CdTe/CdMgTe HETEROSTRUCTURES
G. Karczewski, J. Jaroszynski, M. Kutrowski, A. Barcz, T. Wojtowicz and
J. Kossut
Institute of Physics, Polish Academy of Sciences Al. Lotnikow
32/46, 02-668 Waszawa, Poland
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_yTe
two-dimensional (2D) single quantum well structures. Modulation doping with
iodine of CdTe/Cd_{1-y}Mg_yTe 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.
PACS numbers: 73.40.Hm
GROWTH AND ELECTRICAL PROPERTIES OF PHOSPHORUS DOPED Zn_{1-x}Mn _xTe
CRYSTALS
Le Van Khoi, J. Jaroszynski, B. Witkowska A. Mycielski, R.R.
Galazka
Institute of Physics, Polish Academy of Sciences Al. Lotnikow
32/46, 02-668 Warsaw, Poland
and J. Cisowski
Department of Solid State Physics, Polish Academy of
Science Wandy 3, 41-800 Zabrze, Poland}
The high pressure Bridgman technique was used to grow
Zn_{1-x}Mn_xTe:P crystals. Under the N_2 pressure of 30 atm., we
obtained the p^+-{\rm Zn}_{1-x}Mn_xTe single crystals 8-10 mm in
diameter, with free-carrier densities as high as
p\approx8\times10^{18} cm^{-3} and the room temperature conductivity
\sigma\rm(RT)\approx30 \Omega^ {-1}cm^{-1}. Magnetoresistance measurements
were carried out down to 1.3 K and up to 6 T. In Zn_{1-x}Mn_xTe:P a
strong increase in the acceptor binding energy as well as an immense
(\rm\rho(0,1.3 K)/\rho(6 T,1.3 K)> 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.
PACS numbers: 71.30.+h, 71.55.Jv, 72.80.Ga
INFLUENCE OF LOCAL POTENTIAL ON EXCITON SPLITTING IN HIGHLY DILUTED Cd
_{1-x}Mn_xTe
L. Klopotowski, M. Herbich, W. Mac, A. Stachow-Wojcik and
A. Twardowski
Institute of Experimental Physics, Warsaw University, Hoza
69, 00-681 Warsaw, Poland
We investigated magnetoreflectance and magnetization of highly diluted
bulk Cd_{1-x}Mn_xTe crystals 0.2%\le x\le10%. The exchange constant
in terms of mean field approximation and virtual crystal approximation (the
ratio of the heavy hole exciton splitting to mean spin per unit cell) was
evaluated and found x-dependent. This deviation from the mean field
approximation and virtual crystal approximation prediction is caused by the
local potential introduced by Mn ions. We discuss the problem within a
Wigner-Seitz approach and within a model of magnetic and chemical disorder
based on the alloy theory.
PACS numbers: 71.70.Gm, 75.10.Dg, 75.50.Pp
LUMINESCENCE DYNAMICS OF EXCITON REPLICAS IN HOMOEPITAXIAL GaN LAYERS
K.P. Korona, J.M. Baranowski, K. Pakula
Institute of Experimental
Physics, Warsaw University Hoza 69, 00-681 Warszawa, Poland
B. Monemar, J.P. Bergman
Department of Physics and Measurement
Technology, Linkoping University 581 83 Linkoping, Sweden
I. Grzegory and S. Porowski
High Pressure Research Center, Polish
Academy of Sciences Sokolowska 29/37, 01-142 Warszawa, Poland
Photoluminescence of excitons and their phonon replicas in
homoepitaxial MOCVD-grown gallium nitride (GaN) layers have been studied by
picosecond (ps) time-resolved photoluminescence spectroscopy. The
time-resolved photoluminescence spectroscopy has shown that the free
excitons and their replicas have the fastest dynamics (decay time of about
100 ps). Then, the excitons-bound-to-donors emission rises (with the rise
time similar to the free excitons decay time) and decays with t=300 ps. The
excitons-bound-to-acceptors has the slowest decay (about 500 ps). It has
been found that the ratio of excitons-bound-to-acceptors and
excitons-bound-to-donors amplitudes and their decay times are different for
1-LO replicas and then for zero-phonon lines, whereas the ratio of amplitudes
and the decay time of the 2-LO replicas are similar to the ones of the
zero-phonon lines.
PACS numbers: 71.35.-y, 78.47.+p, 78.55.Cr