Annual Report 2005 - IPHT Jena

LASERTECHNIK / LASER TECHNOLOGY
Dank besonderem Engagement aller Mitarbeiter
konnte der Bereich Lasertechnik 2005 trotz der
verschärften Situation bei den öffentlichen Fördermitteln
und des allgemein geringen Wirtschaftswachstums
sein Niveau bei den Drittmittelprojekten,
Veröffentlichungen und Patenten wenigstens
in etwa halten. Das Drittmittelaufkommen von rund
1,0 Mio “ liegt merklich unter dem Niveau des Vorjahres
(1,2 Mio “). Insgesamt haben jedoch die
mit dem Umzug erreichten kurzen Wege zu den
anderen IPHT-Forschungsbereichen einen deutlichen
Zuwachs bei der bereichsübergreifenden
Zusammenarbeit bewirkt.
generally poor rate of economic growth. The project
funds in 2005 of about 1.0 Mio are close to
the amount of 2004 (1.2 Mio “). Overall the move
to the Beutenberg campus yielded, however, a
considerable strengthening of trans-divisional
cooperation due to the short distances to the
other IPHT research divisions.
4.2 Selected Results
4.2.1 Laser chemistry
Laser chemistry at IPHT is essentially concerned
with the deposition of thin films and thin film systems,
their physicochemical modification (particularly
laser crystallisation) and some special
items like spectroscopic diagnostics of thin film
processing, nanowire preparation, and fs laser
micromachining.
Laser crystallisation
(Gudrun Andrä, Joachim Bergmann,
Arne Bochmann, Fritz Falk, Annett Gawlik,
Ekkehardt Ose)
For several years, IPHT has been aiming at the
preparation of thin film solar cells consisting of
large grained crystalline silicon on glass. The
development of this new cell type is based on the
deposition of amorphous silicon either by plasma
CVD from SiH 4 (13.6 MHz) or by electron beam
evaporation of bulk silicon and its in situ laser
crystallisation. In a first step large crystal grains
are obtained from 300–500 nm thick amorphous
silicon layers by cw laser crystallisation (seed
layer formation). Subsequently the seed layer
undergoes epitaxial thickening by pulsed Layered
Laser Crystallisation (LLC), an IPHT patented
method. So far laboratory cells with an open circuit
voltage of 510 mV and a conversion efficiency
of 4.8% based on an absorber thickness of
5 µm were obtained. Recent work addressed the
acceleration (industrial application) and optimisation
of the seed layer formation by applying a
700 W diode laser focused to a line and scanned
across the substrates to achieve crystallite sizes
of 0.1 to several mm (cf. coloured page). Additional
progress for the solar cell performance is
expected from improving light trapping, improving
contact and shunt resistances as well as minimising
charge carrier recombination. The related
work benefits from the discussions and cooperation
with the Hahn-Meitner-Institute (HMI) at
Berlin, Solar-Zentrum Erfurt at CiS, Ersol company
at Erfurt, and INPUT Solar, a Thuringian association
of photovoltaic industrial companies and
R&D institutes.
Thin film deposition and nanowire growth
(Gudrun Andrä, Fritz Falk, Herbert Stafast,
Thomas Stelzner)
The deposition of Si/C/N thin films for tribological
applications by RF plasma enhanced CVD using
single source precursors was performed within
the DFG program SPP 1119 in close cooperation
with TU Darmstadt and RWTH Aachen. IPHT
contributed to the understanding of the complex
CVD processes by comparing Si/C/N thin films
obtained from two precursors, hexamethyldisilazane
(CH 3 ) 3 Si-NH-Si(CH 3 ) 3 (HMDS) and
bis(trimethylsilyl)carbodiimide (CH 3 ) 3 Si-N=C=N-
Si(CH 3 ) 3 (BTSC). Hard Si/C/N thin films were
obtained on the RF powered, but not on the
grounded electrode. Therefore a heating system
for the RF electrode was developed which
allowed to investigate the substrate temperature
dependence of the thin film properties. As an
example the temperature dependence of the film
hardness is sketched out in Fig. 4.1.
Fig. 4.1: Martens hardness of Si/C/N thin films
obtained from HMDS or BTSC as a function of
the subtrate temperature.
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