European Commission
Future and Emerging Technologies
MICROELECTRONICS ADVANCED RESEARCH INITIATIVE
MEL-ARI OPTO
3rd Annual Workshop
Athens, October 13-15, 1999
Poster presentations abstracts
Structural, optical and
nanocomposite layers.
V.G.Baru, A.P.Chernushich,
A.A.Timofeev*, L.Yu.Zaharov.
luminescent
M.I.Elinson,
V.A.Jitov,
properties
V.I.Pokalyakin,
of
SiNx
G.V.Stepanov,
Institute of Radio Engineering and Electronics of Russian Academy of Sciences, Mohovaja
11, Moscow, RF.
*Moscow Engineering and Physics Institute, Kashirskoe shosse, 31, Moscow, RF
The development of Si based LED is necessary for optical interconnections in silicon
VLSI and other applications.
Therefore the fabrication and research of nanocrystalline Si layers are actual.
We investigated the structural, optical and luminescent properties of nanocomposite
layers containing Si nanocrystals (Si NC) in SiNx matrix. The layers were obtained on
different substrates by sputtering of cSi target in Ar and N2 atmosphere. The structure
and properties of layers depended on Si surplus and subsequent annealing. The Si
surplus was determined by sputtering velocity and by Ar and N2 pressures. The layers
with relative low Si surplus shown photoluminescence (PL) in wide spectral region
(λ= 400-800 nm).
The annealing of layers in vacuum (T = 1000-1100 C, t = 10-30 min) sharply
enhanced (more than on the order) intensity PL especially in the field of a maximum
of a spectrum (λ≈ 500-600 nm, see Fig.1). The optical spectra of a transmission and
reflection weakly depend on an annealing at λ> 400 nm. The structure of layers was
investigated by methods of TEM and of a microdiffraction (JEOL-2000). The
annealing (since 700C) was accompanied by growth of concentration Si NC with
sizes 2-3 nm. The diffraction picture also confirmed presence small-sized NC of
various orientation. The growth of intensity PL after an annealing correlates with
increasing of concentration small-sized NC. However growth of sizes NC during an
annealing does not influence on PL spectral structure in particular on a position of a
maximum of a spectrum. Probably important role in PL is played by specific defects
near to the boundary NC- matrix.
In the layers with high Si surplus PL decreased up to disappearance. In this case the
layer structure is change according TEM pictures. The Si surplus in such layers is
mainly as big (10-50 nm) amorphous or crystalline clusters. The PL disappearance is
connected with sharp increasing of non radiative recombination in layers.
The electroluminescence (EL) in SiNx layers are investigated mainly in Au-SiNx-pSi
structure with transparent Au contact. Noticeable EL was observed on a return branch
I-V characteristic (“-“ on pSi). The I-V characteristic had a superlinear form.
Spectrum EL (λ≈ 400-800 nm) had a maximum in long wavelength area (800-900 nm,
Fig.2). The EL intensity depend on a type and conductivity of a substrate, potential
polarity, thickness of a layer, it's structure etc. The mechanisms PL and EL in
EL of Au-SiNx-pSi structure at 50 mA current.
0.6
0.5
EL, a.u.
0.4
0.3
0.2
0.1
0.0
400
500
600
700
800
900
Wave length, nm
obtained layers are probably different. Conditions of the transport and injection of
current carriers are very essential for EL.
This research was supported by INCO Project Grant N977037.
PL of SiN x layer on cSi substrate
2.0
PL, a.u.
1.5
After vacuum annealing at 1100C, 10 min
1.0
Before annealing
0.5
0.0
300
400
500
600
700
Wave length, nm
Fig.1
Fig.2
800
900
Low temperature Si-Si and GaAs-Si direct wafer bonding using spinon-glass intermediate layer
M. Alexe, V. Dragoi, M. Reiche, and U. Gösele
Max Planck Institute for Microstructures Physics
Weinberg 2, D-06120 Halle (Saale), Germany
In the last years, direct wafer bonding has emerged as a powerful and versatile
technology for microelectronics, optoelectronics and micromechanics. Usually after
the room temperature bonding the interface energy is increased by a thermal
annealing at high temperatures. Applications that involve bonding of processed
wafers or of dissimilar materials with high thermal expansion coefficient mismatch
require low temperature annealing. The present paper propose a new low temperature
bonding technique using Spin-on Glass (SOG) as intermediate layer. Low temperature
bonding using SOG intermediate layer was successfully applied to bond Si/Si and
GaAs/Si
Thin films of SOG (about 2400 Å thick) were deposited by spinning on 4 inch
diameter silicon wafers using as glass precursor commercially available silicate SOG.
After deposition the SOG films were baked in air at 150°C onto a hot plate. The SOG
coated wafers were bonded with plain silicon wafers. The interface energy measured
for the bonded wafers was about 0.46 J/m2.After bonding the wafers were annealed at
200°C in air for different times. The value of the interface energy increased to 2.3
J/m2 for 18 hours annealing. In order to prove that the bonding interface energy is
sufficient to sustain further mechanical processing samples realized by bonding via
SOG and annealed at 200°C for 10 hours were submitted to standard grinding and
polishing. After the mechanical processing the wafer was thinned up to 5.5 µm.In
order to investigate the behavior of the bonded interface at higher temperatures the
wafer pair was heated up to 400°C.
The SOG bonding was also proved in the case of GaAs/Si. Si wafers coated with SOG
as described in the previous section were bonded directly to commercial 4 inch
diameter GaAs wafers. The room temperature bonded wafers were submitted to
thermal annealing for 12h at 200°C and 225°C. After the annealing at 225°C the
GaAs/Si bonded interface energy reaches 1.7 J/m2. As in the Si/Si case the energy is
sufficiently high to sustain further processing. The bow (stress) measurement reveals
a very high bow developed at the annealing step. The bow and stress in the case of
GaAs/Si is high at high temperatures, but comes back to zero at room temperature.
This can be due to SOG film which allows the bonded wafers to glide without
affecting the bonded interface. Therefore, we can conclude that the stress in the bulk
wafer is actually lower than the one which can be simply calculated considering an
incompliant GaAs/Si interface and the SOG layer help to relax most of the stress even
after acquiring a high interface energy. Part of GaAs/Si wafers were submitted to
thermal annealing at temperatures higher than 200°C. GaAs/Si samples were
submitted to further grinding and polishing of either GaAs or Si to extract within
further experiments the maximum temperature which can be attained without
damaging the wafers or the bonding interface. Providing the surfaces have achieved
the bondability conditions, the described process is readily applicable in the case of
processed Si wafers and epitaxially deposited GaAs but only after submitting them to
planarization processes.
Mechanisms of carrier transport and electroluminescence in SI/CAF2
quantum wells
V.Ioannou-Souglerides, V.Tsakiri, A.G.Nassiopoulou
IMEL /NCSR Demokritos,
PO Box 60228 153 10 Aghia Paraskevi, Athens Greece
S. Ménard, M. Liniger, F. Bassani, F. Arnaud d’Avitaya
Centre de Recherche sur les Mécanismes de la Croissance Cristalline
Campus de Luminy - case 913, 13288 Marseille cedex 9, France
A. N. Kholod, V. E. Borisenko
Belarusian State University of Informatics and Radioelectronics
P. Browka 6, 220027 Minsk, Belarus
An experimental and theoretical research focused on charge carrier transport and
electroluminescence in quantum well structures formed by alternated nanosize layers
of Si and CaF2 has been undertaken within the ESPRIT project SMILE.
In the theoretical analysis performed direct carrier tunnelling (described by WentzelKramers-Brillouin approximation), resonant tunnelling and carrier trap mediated
tunnelling have been compared. While the first one yields monotonous I-V
characteristics, the two others result in the regions with a negative differential
resistance (NDR) on the I-V curves. Non-monotonous I-V curves with the well
resolved region of NDR were experimentally registered at room temperature and
studied in details for Si/CaF2 one-, two-, five-, and fifty-wells structures. The I-V
characteristics have been found to be asymmetric with respect to the current origin
and shifted along the voltage axis. The experimental regularities observed meet
appropriate explanation within the model accounting for carrier trapping in the barrier
material.
The dielectric properties fifty-periods quantum wells were investigated by
capacitance-voltage and conductance-voltage measurements over the temperature
range 75-320 K. Samples with different thickness in each bilayer in the range of 1.43 nm for CaF2 and 1.6 nm for Si were used. The results indicated that the whole
multilayer structure behaves as a MIS capacitor. The characteristics strongly
depended on CaF2 layer thickness. The interface between Si substrate and the
quantum well structure is characterized by a moderate density of states. Charge buildup in the structure takes place during the voltage sweep. The discharging process has
very high time constants. This leads to strong hysteresis effects.
Room temperature electroluminescence was experimentally studied and theoretically
simulated in Si/CaF2 multi quantum well structures. The experimentally observed
coincidence of photo- and electroluminescence spectra has allowed to conclude that
identical interband carrier recombination mechanisms are involved in both cases. In
order to optimize efficiency of the electroluminescence a model was developed. It has
predicted that maximum intensity can be achieved in the structures composed of 1520 periods. Comparison of experimental and theoretical results is discussed.
A study of the optical properties of Fe within structures containing Si
and Ge.
C. N. McKinty, A.K. Kewell, J.S. Sharpe, M. A. Lourenco, T. M. Butler, K. J. Reeson Kirkby
and K. P. Homewood
 - FeSi2 has been shown to have a minimum direct band gap of 0.87eV, which leads
to the opportunity for Si based optoelectronics, optical communications and optical
interconnects. Electroluminescence has been reported from structures containing  FeSi2, which were produced by ion implantation.[1] 1
In this investigation we report preliminary results on optical properties when using
Si(1-x)Gex epitaxial layers as the implant matrix for Fe.
1
D.Leong, M. A. Harry, K. J. Reeson, K. P. Homewood. Nature, Vol 387, 12 June 1997, p. 686-688
Erbium as emitter in amorphous semiconductors: a-Si:H and related
alloys
H. Kühne1), G. Weiser1), E. Terukov2) and M. Bresler2)
1)
2)
Fachbereich Physik, Universität Marburg, D-35032 Marburg, Germany
Ioffe Physico-technical Institute, 194021 St. Petersburg, Russia
Erbium ions show in hydrogenated amorphous silicon efficient photoluminescence at
1.5µm which is much stronger than in c-Si and retains at room temperature still about
10 - 20% of its strength at low temperature. The advantage of a-Si:H as host for Er
ions lies in the great flexibility of an amorphous lattice which allows to incorporate up
to 1020 Er/cm3 without loss of efficiency, a key factor for strong Er luminescence.
Detailed investigation in the first year of the project show that Erbium ions are excited
via a resonant non-radiative energy transfer from recombination of electron hole pairs
at dangling bonds in a-Si:H. Efficient transfer requires optimisation of carrier
relaxation through band tails into the resonance window for the energy transfer to Er
ions and reducing radiative and non-radiative recombination within the host2.
Most studies were performed on samples prepared by a magnetotron assisted silane
decomposition (MASD-process) which yields a homogeneous distribution of Er ions
but material of poor electronic quality since this process creates a high concentration
of dangling bonds (1018/cm3), the main centres for non-radiative recombination.
Consequently, electroluminescence of Er ions is weak and observed so far only under
high reverse bias. However, since dangling bonds are also involved in the energy
transfer to Er it was not clear whether their number could be reduced without losing
the Er emission.
The concentration of dangling bonds has been reduced by a new deposition process
which is based solely on plasma decomposition of silane and a sufficiently volatile
metal-organic Er compound. First samples show improved photocurrent while ESR
studies confirm a reduction of dangling bonds by an order of magnitude. Despite the
reduced dangling bond density the Er-luminescence has improved, indicating that
dangling bond density and Er concentration can be optimised separately. SIMS and
Rutherford backscattering studies reveal a very inhomogeneous distribution of Er ions
which should be overcome by better control of the partial pressures of silane and the
Er compound. Under the present deposition conditions most of the large organic
constituents of the Er compound are incorporated which leads to a large concentration
of carbon in the films. The SIMS and RBS studies show also that most of the oxygen
atoms which link Er to the organic side groups are also incorporated into the film,
presumably surrounding the Er ions. A large concentration of oxygen has also been
beneficial for the Erbium emission in MASD films and in c-Si3.
2
3
H. Kühne, G. Weiser, E.I. Terukov, A.N. Kuznetsov, V.Kh. Kudoyarova, in print J. Appl. Phys.
S. Coffa, G. Franzó, F. Priolo, A. Polman and R. Serna, Phys.Rev. B 49, 16313 (1994)
The route to the stable high-effective LED and PD in the Si-chip with
optical intra-chip interconnect: self-formatted Si nanocomposites
from PS at the Metal/PS interface.
E.Buzaneva
National Kiev Taras Shevchenko University,
64, Vladimirskaya Str,252033 Kiev-33,Ukraine
The idea of innovative nanoengineering of metal-porous Si (PS) interface in Si-chip
with optical intra-chip interconnect(metal electrodes for LED,PD and alumina/TiO2
waveguide) and the results of its experimental examination are present.
Nanoengineering is the stimulation of the self-formation of Si nanocomposites from
PS at the metal/PS interface. Self-formation of the Si nanocomposites with predicted
physical and optical properties allows to control, optimize and stabilize, high-effective
parameters of LED, PD in the Si-chip.
For example, in the Si chip with Al electrodes for LED, PD in the result of the solid
phase processes between Al and PS such as the Si diffusion into Al and the reverse
diffusion, the dissociation of the solid solution Si in Al film, the interaction of Al with
Si oxides and the dielectric of AlOSi type formation may occur at Al/oxidized PS
interface by the analogy with the processes at Al/monocrystalline-Si (c-Si) interface.
In this case the interface layer may be consisted of: (i) self-formed Si nanocrystallites
in (nc-Si):SiOx:SiyOz nanocomposite; (ii) Si nanocrystallite, picked out at cooling
from the solid solution; (iii) SiOx(SiyOz) partially substituted by AlOSi forming ncSi:SiOx:SiyOz:AlOSi nanocomposite. The Si nanocrystallite size in PS may be
decreased due to the Al diffusion into PS and AlOSi formation. So, the PL and EL
contribution of this layer to green PL and EL is considered to be predominant. Then if
the PL is caused by band-to-band recombination in nc-Si (the linear dimension of Si
spherical nanocrystallite is 2,5 nm and Eg =2,3 eV at 300K ) then the green PL will be
prevailed.
The expermental examination of the idea was made on the Si chips and their
elements, which had been produced by Dr. S.Lazarouk4. The stable strong yellowgreen EL has been observed on the edge of Al-electrodes to the oxidized PS. Alelectrodes border upon alumina layer of the WaveGuide, formed by electrochemical
anodization. To form Al-electrodes in LED and PD the Al film covering (1 mm) by
magnetron sputtering at 520 K on the oxidized PS was used.
To confirm experimentally the developed concept of the Si nanocomposite from PS
self-formation we have considered: the composition of the nc-Si:SiOx :SiyOz:AlOSi
layer by XPS and IR spectroscopy; the detection of the presence of Si nanocrystallites
by XPS, using the Si core level electron spectra and the shift of valence band edge for
nc-Si; the definition of Si nanocrystallite size by Raman spectroscopy using the
simulation of the Raman line shape at wavelength of 450-550 cm-1 (this was made by
us and the group of prof. S.Bayliss, UK)
4
S.Lazarouk, P. Jaguiro, V. Borisenko, Physica of Status Solidi(a)165(1998)87
Photophysical properties of nc-Si:SiOx,:SiyOz and nc-Si:SiOx :SiyOz:AlOSi
nanocomposites namely: the PL shape and its peak situation; the reflectance and the
refractive index of the nanocomposites in the visible range are revealed to be depend
on the dielectric of AlOSi type presence and Si nanocrystallite size.
Ion beam synthesised FeSi2 - development of band gap & structure
during annealing
A.Belson1*, D.Bransted1, C.Dawes1, S.Mashford1, H.Sunnucks1*, J.S.Sharpe2,
C.N.McKinty2, M.Kerford2, M.A.Lourenço2, A. Kewell2, T.Butler2, K.P.Homewood2,
C.Jeynes2, R.P.Webb2 and K.J.Reeson Kirkby2
*Maidstone Grammar School,Kent
The Cavendish School, Hemel Hempstead
Grange School, Hertford, Cheshire
The Hayfield School, Doncaster, S.Yorkshire
1
CREST Master Class 99 1School of Electronic Engineering, Information Technology &
Mathematics, University of Surrey, Guildford, Surrey, England
2
School of Electronic Engineering, Information Technology & Mathematics, University of
Surrey, Guildford, Surrey, England
Practical silicon based optoelectronics has long been a goal of the semiconductor
industry. Since this would allow circuit and optical components to be integrated on a
single chip. Light emission at 1.5µm is also desirable as this corresponds to the
wavelength window utilised in optical fibres. The  phase of FeSi2 has attracted
considerable research interest, in recent years, because of its semiconducting
properties. In particular, interest has focussed on the nature of the band gap and its
magnitude. Using high dose ion implantation followed by annealing (ion beam
synthesis (IBS)), direct band gap FeSi2 can be fabricated, with a band gap of around
0.87eV (~1.5µm).
In this study, a (100) silicon wafer was implanted with 2 x 1017Fe cm-2 at 200keV.
During implantation the wafer was heated to ~500°C using the power of the incident
ion beam. Subsequent to implantation the wafer was cut into smaller samples, two of
which, underwent sequential isochronal annealing (600°-900°C in steps of 100°C,
900°C-990°C in steps of 10°C) for times of 60 seconds. One sample was examined
by Rutherford Backscattering and ion channelling after each annealing step, the other
was used for optical absorption measurements.
As the annealing temperature was increased up to 800°C, the approximately gaussian
distribution, observed after implantation became more rectangular in profile and
shoulders appeared at the wings. This behaviour was similar to that observed in
cobalt implanted samples. Unlike Co, however, annealing above 900°C caused the
distribution to broaden suggesting that iron diffusion was occurring, from the centre
to the wings of the distribution. As the annealing temperature was increased the band
gap decreased, this decrease was more marked at the higher annealing temperatures
and could be linked to the outward iron diffusion. It is speculated that, at the higher
annealing temperatures, the samples contain both semiconducting FeSi2 and the
metallic  phase, which contains approximately 18% iron vacancies and is usually
formed above 940°C.
Optical and Electrical Properties of (Si/SiO2)n Multi-Layers Prepared
by a CMOS Compatible Process
G. Pucker, V. Mulloni, C. Mazzoleni, Z. Gaburro, L. Pavesi
INFM and Department of Physics, University of Trento
Via Sommarive 14, 38050 Povo-Trento, Italy.
P. Bellutti, M. Bersani, L. Vanzetti, M. Sbetti
ITC-IRST, 38050 Povo-Trento, Italy
The lack of efficient Si light emitting devices limits the development of Si based
optoelectronics. Research in this area was stimulated by the discovery of intense
visible light emission in porous Si formed by electrochemical etching of Si5. Beside
research on light emitting Si-nanocrystals and porous Si, (Si/SiO2)n multi quantum
wells attracted interest. Lockwood et al. showed photoluminescence from amorphous
Si prepared by MBE6,whereas Heikkilä et al. obtained electroluminescence from
Si/SiO2 multiquantum wells prepared by LP-CVD7.
Aim of the present study is to develop a process, which allows the preparation of
poly-Si/SiO2 multilayers, showing photo- and electro-luminescence, by a CMOS
compatible process, and to test the performance of the multi-layers in simple LEDs.
Poly-Si layers thinner than 3 nm are prepared from 15-20 nm thick poly-Si layers by a
two step re-oxidation process. The samples show broad photoluminescence ranging
from 700 to 900 nm similar to the one observed for Si nanocrystals 8. The emission
wavelength and FWHM can be tuned by implanting the emitting layers within a
microcavity consisting of Si and SiO2 layers. The FWHM of the cavity mode is less
than 10 nm at 640 nm for DBRs consisting of just two periods.
We will present photoluminescence measurements of (Si/SiO2)n multilayers as
a function of n and poly-Si thickness together with the photoluminescence spectra of
microcavities activated by Si/SiO2 multilayers, discuss the influence of annealing on
the photoluminescence, and show I-V measurements on (Si/SiO2)n multilayers with
different n-values. Results of the investigation of SiO2/Si/SiO2 quantum wells with
SIMS and XPS will be presented.
The study is part of the project SMILE within the ESPRIT-MEL ARI cluster.
5
L. T. Canham, Appl. Phys. Lett. 57 (1990) 1046.
D. J. Lockwood, Z. H. Lu, J. M. Baribeau, Phys. Rev. Lett. 76 (1996) 539.
7
L.Heikkilä ,T. Kuusela, H.-P. Hedman, Ihantola, Appl. Surface Science 133 (1998) 84.
8
T. Inokuma, Y. Wakayama, T. Muramoto, R. Aoki, Y. Kurata, and S. Hasegawa, J. Appl. Phys. 83
(1998) 2228.
6
Components for 1 Gbit/s/channel, 2-D Array Optically
Interconnected CMOS for the OIIC ‘GigaLink’ Demonstrator
J.P.Hall1, R.Baets2, R.Annen3, P.Zenklusen3, K.J.Ebeling4, A. Neyer5, B.Wittmann5,
V.Baukens6, H.Thienpont6
1
Marconi Materials Technology, Caswell, Towcester, Northants, NN12 8EQ, U.K.
IMEC-INTEC, Sint-Pietersnieuwstraat, Gent, B-9000, Belgium
3
Swiss Federal Institute of Technology, ETH-Hoenggerberg, HPT, CH-8093 Zurich,
Switzerland
4
University of Ulm, Albert-Einstein-Allee 45, D-89069 Ulm, Germany
5
Universität Dortmund, Otto-Hahn-Str.6, D-44221 Dortmund, Germany
6
Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussel, Belgium
2
Fast, dense optical interconnect for inter-chip (and ultimately intra-chip) applications
will be needed to ensure that the interconnect technology keeps pace with
developments in IC technologies. Within the MEL-ARI ‘OIIC’ project a ‘GigaLink’
optical interconnection concept is being developed in which 2D array interconnection
between CMOS chips, operating at 1 Gb/s per channel, is envisaged. A 2 x 8
demonstrator system is being designed and built. The transmitter section uses an array
of sources set on a 250 µm pitch, flip-chip hybrid-mounted onto an array of driver
circuits fabricated on a section of a CMOS chip. Two variants are covered, using
VCSEL and RC-LED sources, both emitting at 850 nm. Results will be presented on
RC-LEDs operating at 1 Gbit/s, on the performance of VCSEL arrays and on the
evaluation of test CMOS driver circuits. The operation of RC-LEDs at 1 Gb/s with
high efficiency necessitates optimisation of the RC-LED itself (in particular in terms
of suitable diameter) as well as of the driver circuit. The receiver function uses a 2 x 8
array of photodiodes, again on a 250 µm pitch, hybrid-mounted onto an array of
receiver circuits fabricated on a section of a CMOS chip. As well as for RC-LEDs, the
size of the detector is very important for high-speed characteristics. Both DC-coupled
and AC-coupled receiver variants are envisaged and results on test chips will be
presented. The optical pathway in this demonstrator is a 2 x 8 array of polymer optical
fibres (POF) with 60 µm core / 120 µm cladding and NA = 0.5 allowing a bend radius
below 2 mm with low loss. The 2D POF ferrules that are to interface to the
CMOS/optoelectronic modules are based on stacked plates with U-grooves holding
the fibres. The resulting ferrule block is passively aligned by pin-mounting onto a
spacer that had been index-aligned and fixed around the CMOS-chip. The scope for
the use of arrays of microlenses to improve the fibre coupling efficiency and relax the
alignment tolerances will be described. Key issues associated with operation at 1 Gb/s
include the impact of crosstalk on BER characteristics, power consumption and
scalability. Operation at 850 nm has been chosen on the basis of both performance
and standardisation and techniques have been developed for removal of the opaque
substrate from source and detector array chips.
Avalanche porous silicon light emitting diodes for optical intra-chip
interconnects
S. Lazarouk1, P. Jaguiro1, S. Katsouba1, N. Gaponenko1, V. Stanovski2, V. Vysotzki2
1
Belarusian State University Informatics and Radioelectronics, P. Browka 6, 220027, Minsk,
Belarus
2
Research and Design Company Belmicrosystems, Minsk, 220600, Belarus
Last time porous silicon is considered as a promising material for Si-based
optoelectronics. Recently we have reported on an aluminum-porous silicon junction,
which can operate as a light emitting diode at bias voltage more than the avalanche
breakdown value and as a photodetector at bias voltages less than this value. In this
work a prototype of optical intra-chip interconnects has been developed and
fabricated. The developed design includes reverse biased aluminum-porous silicon
diodes connected optically by an alumina waveguide. Some parameters of the
fabricated optoelectronic components have been measured. The time response for
signal output in the developed light emitting diode - photodetector system was about
ten nanoseconds. The investigated design can be integrated with electronic circuit
components on the same Si chip, because the used technological operations are
compatible with silicon IC technology. Possible applications of the developed
optoelectronic system have been discussed.
Deep level transient spectroscopy of silicon / iron disilicide light
emitting devices
M. A. Lourenco, R. M. Gwilliam, A. Kewell, C. McKinty, J. Sharpe, T. Butler, K. J. Reeson,
and K. P. Homewood
The School of Electronic Engineering, Information Technology & Mathematics,
University of Surrey, Guildford, Surrey, United Kingdom
Iron implanted silicon layers are recently attracting great interest due to the successful
fabrication of ion beam synthesised ß-FeSi2 light emitting devices formed by ion
implantation. The optimum fabrication conditions of such devices are still under
investigation, so the characterisation of the defects distributions in these structures is
of crucial importance. We report here a Deep Level Transient Spectroscopy (DLTS)
study of the electrically active defects observed in Fe implanted silicon substrates and
ß-FeSi2 light emitting devices fabricated under various conditions. The distribution
and concentration of the deep levels is analysed as a function of the implant
parameters such as energy, dose, current and temperature. We also compare the defect
distribution of light emitting devices fabricated entirely by implantation (where both
the p-n junction and the silicide are formed by ion implantation) and of devices
formed by implanting Fe into epi-substrates.
Symmetry and passivation dependence of the optical properties of
nanocrystalline silicon structures
Elena Degoli, Stefano Ossicini
Istituto Nazionale per la Fisica della Materia (INFM) and Dipartimento di Fisica,
Universita` di Modena e Reggio Emilia, via Campi 213/A, I-41100 Italy
The electronic and optical properties of silicon multi-quantum wells, as a function of
their symmetry and passivating species, are studied ab-initio by means of the linear
muffin-tin-orbital method.
The role of symmetry has been investigated considering both (111) and (001) silicon
surfaces passivated with hydrogen. We find that the symmetry of the lattice changes
the nature of the gap that is indirect in the Si-H(111) saturated QW's and becomes
direct in the Si-H(001) ones. This result supports the idea that symmetry
considerations can play an important role for the optical response of confined Si
wells.
The role of passivation has been studied using CaF2 and SiO2 to saturate the dangling
bonds of Si. We found that the saturating species play an important role in the
formation of interface states that can occupy or leave free the band gap so improving
or making worse the optical properties of the material. We study the Si-SiO2 quantum
wells not only to evidentiate the role of oxygen and oxygen related defects in the
optoelectronic properties, but also in order to compare our theoretical results with the
experimental data of Kanemitsu9 Mulloni10, Lockwood11 and Novikov12. For the SiSiO2 confined quantum wells we use, at the interface, the -cristobalite model. Our
results show that the system, with and without defects, is still a semiconductor with a
band gap larger than in the case of bulk silicon. The analysis of the optical properties
shows the presence of several peaks in the low energy optical region (between 1.0 and
2.2 eV) in both cases and the important role played by oxygen related defects in the
determination of the optoelectronic properties of the material.
9
Photoluminescence from Si/SiO2 single quantum wells by selective excitation, Y. Kanemitsu, S.
Okamoto, Phys. Rev. B 56, (1997) R15561;
10
All Porous silicon optical devices and Si/SiO2 multilayers: recent results, V. Mulloni, R. Chierchia,
C. Mazzoleni, G. Pucker, L. Pavesi and P. Bellutti, (submitted to Philosophical Magazine B);
11
Quantum confined luminescence in Si/SiO2 superlattices, D. J. Lockwood, Z. H. Lu and J.-M.
Baribeau, Phys. Rev. Letters 76 (1996) 539;
12
Visible luminescence from Si/SiO2 superlattices, S. V. Novikov, J. Sinkkonen, O. Kilpelä, S. V.
Gastev, J. Vac. Sci. Technol. B 15 (1997) 1471.
Effect of cobalt implantation on the material and optical properties
of -FeSi2 precipitates
T.M. Butler1, K.P. Homewood1, K.J. Reeson Kirkby1, A.K. Kewell1, M.A. Lourenço1, C.N.
McKinty1, J.S. Sharpe1, R.M. Gwilliam1 and G. Shao2
1
School of Electronic Engineering, Information Technology & Mathematics
School of Mechanical and Materials Engineering
University of Surrey, Guildford, Surrey GU2 5XH UK
2
-FeSi2 layers, produced by ion beam implantation of iron into (100) silicon, were
implanted with small amounts (<20%) of cobalt ions. The iron was initially implanted
at a dose that would be insufficient to form a continuous layer. After suitable
annealing precipitates of -FeSi2 are formed. This study investigates the systematic
addition of cobalt and the resulting change in the properties of these -FeSi2
precipitates. Issues investigated include the change in the  to  transition
temperature with increasing cobalt concentration, and the change in the band-gap
energy of the semiconducting silicide. A range of characterisation methods were used
to study the resulting (Fe1-xCox)Si2 silicide. These included TEM and x-ray
measurements on the material side, and optical absorption and FTIR measurements on
the optical side.
Modeling and design of low-loss Oxidised Porous Silicon Waveguides
H.F. Bulthuis, F. M. van der Vliet, H. van Weerden
BBV Software BV, Hengelosestraat 705
7521PA Enschede, The Netherlands. E-mail: bbv@bbv.nl
M.Balucani, V. Bondarenko, E. Fazio, G.Lamedica, A. Ricciardelli, E. Viarengo,
A.Ferrari
INFM Unita di Roma, Dipartimento di Ingegneria Elettronica, Universita 'La Sapienza' di Roma,
Via Eudossiana 18, 00184 Roma, Italy
J.E. Broquin, G. Vitrant
Institut National Polytechnique De Grenoble, Laboratoire d’Electromagnétisme, Microondes et
Optoélectronique, Avenue Felix Viallet 46, 38031 Grenoble, France
Abstract
In this presentation simulation results of OPWG’s, Optical Porous Silicon Waveguides, will be
presented. Porous Optical Silicon Waveguides are of interest because the technology of fabricating
them is compatible with the established CMOS technology used to build electronics devices,
making the OPSWG’s serious candidates for optical interconnects on future ULSI chips. The
optical interconnects should have low-loss in the infrared and one should be able to bury them. In
addition one would like to achieve small on-chip bend-radii and have means of vertical incoupling
of light, eg. by VCSEL, as well as vertical outcoupling of light, facilitating detection. The light in
the OPSWG is confined in dense Silica surrounded by a buffer of oxidised porous Silicon. From our
studies it is shown that the main loss-mechanism in these waveguides is due to tunneling of light
throught the oxidised porous buffer into the Silicon substrate having very large refractive index
compared to the dense Silica core. Simulation results will also be shown for OPSWG’s in bends as
well as calculations for ultra-short bends used in redirecting light by 90 degrees in the end-facet of
the OPSWG channel. Measured propagation losses of the best waveguides fabricated so-far are O(
1 dB/cm) which is in good correspondence with the propagation losses calculated by using a newly
developed leaky mode-solver.
Wafer
surface
b
Sem-picture of OPSWG after etching
Calculated fundamental Measured near field picture of
lossy mode.
the semi-guided mode.
Investigation of performance capabilities of emitters and detectors based on a
common MQW structure
E. Aperathitis, D. Cengher, Z. Hatzopoulos, K. Amimer, C. Michelakis, M. Androulidaki, G. Deligeorgis, P.
Tzanetakis and A. Georgakilas
FORTH/IESL and Univ. Crete/Physics Dpt., Microelectronics Research Group, P.O. Box 1527, 71110
Heraklion-Crete, Greece
The integration of GaAs-based optoelectronic devices and Si circuits using GaAs-Si wafer bonding
technology, with fully processed Si circuits on the Si wafer, requires: (i) high quality epitaxial GaAs
wafers, with no defects or layer steps on the surface (regrowth), for successive bonding, and (ii)
processing technology for the fabrication of different kinds of optoelectronic devices (lasers,
photodetectors) from the same single-growth epitaxial GaAs/AlGaAs wafer. Thus, we investigated
the use of the same multiple quantum well - separate confinement heterostructure (SCH-MQW)
for the fabrication of different devices.
Photodetectors (PDs) based on three SCH-MQW structures (with 2, 4 and 8 QWs) were studied for
two types of devices: guided wave and non-guided wave devices. Non-guided wave devices were
processed and their capacitance and responsivity (A/W), in the wavelength range of 750-900 nm,
were determined for various bias voltages. Zero volt bias responsivities were 0.012 A/W, 0.026
A/W and 0.133 A/W, at the LD emission wavelength, for the 2, 4 and 8 QW structures,
respectively. Guided wave PDs were simulated using the transfer matrix method for optical mode
calculation. The absorption coefficient for the fundamental mode was used to calculate the
minimum size of the detectors. The junction capacitance of the guided wave PDs was calculated
from the measured capacitance of non-guided wave devices and the required length for absorbing
98% of the LD light; values of 215 fF, 101 fF and 52 fF were obtained for 2, 4 and 8 QWs.
LD devices were also modeled and fabricated by the three different SCH-MQW structures.
Threshold current densities (Jth) of 737.2 A/cm2, 755.8 A/cm2 and 833.8 A/cm2 were measured for
2, 4 and 8QWs, respectively. Further improvement could be achieved using GRINSCH-MQW
structures and LDs with 4QWs exhibited 33% decrease in Jth and 22% increase in slope efficiency.
The presented results have established the range of specifications that can be achieved with the
single epitaxial growth approach using the same GaAs/AlGaAs laser diode structure and suggest
that there is no critical limitation in the selection of the number of QWs, in the range of 2-8, for
achieving both emitting and detecting devices with the required performances for optical
connections.