Plenarvorträge - DPG-Tagungen

Halbleiterphysik Donnerstag
nes Germanium aufgefasst werden. Laterale Variationen im strukturellen
Übergang machen sich im Wesentlichen in der zweiten und dritten Lage
bemerkbar.
[1] N.I. Borgardt et al., Ultramicroscopy 90 (2002), 241.
HL 44.63 Do 16:30 Poster A
Reifung von Versetzungsringen in Silizium während Aluminiumgettern
— •Carsten Rudolf, Yue-Lin Huang und Michael
Seibt — IV. Physikalisches Institut der Universität Göttingen, Tammannstrasse
1, D-37077 Göttingen, Deutschland
Wir haben die Reifung von extrinsischen Versetzungsringen in Si
während Aluminiumgettern (AlG) untersucht. Das Ziel war herauszufinden,
ob beim AlG an der Grenzfläche zwischen der Al:Si-Schmelze
Eigenfehlstellen entstehen und in das Si-Substrat eindiffundieren.
Extrinsische Versetzungsringe sind Ausscheidungen von Eigenzwischengitteratomen
und reagieren auf Ströme von Eigenfehlstellen durch
Wachstum oder Schrumpfen. Mit Dunkelfeld-Transmissionselektronenmikroskopie
haben wir die Anzahl der in den Versetzungsringen
gespeicherten Atome vor und nach AlG sowie in Referenzproben ohne
Al-Schicht in Abhängigkeit von der Dauer der Temperaturbehandlung
gemessen.
Der Vergleich der gegetterten Proben mit dem Ausgangsmaterial deutet
auf eine schwache Injektion von Eigenzwischengitteratomen hin. Die
Messungen an den Referenzproben zeigen allerdings eine vergleichbare
Injektion, so dass sich insgesamt schließen lässt, dass das AlG die Konzentration
von Eigenfehlstellen nicht wesentlich beeinflusst.
HL 44.64 Do 16:30 Poster A
UHV-wafer bonding of heterostructure semiconductor materials
using low energy hydrogen ion beam surface cleaning
— •Nasser Razek 1 , Axel Schindler 1 , Volker Gottschalch 2 ,
Gerald Wagner 3 , and Bernd Rauschenbach 1 — 1 Leibniz-Institut
für Oberflächenmodifizierung e. V., Permoserstrasse 15, D-04318 Leipzig,
Germany — 2 Universität Leipzig, Institut für Anorganische Chemie,
Linnestr. 3, 04103 Leipzig — 3 Institut für Nichtklassische Chemie e. V.,
Permoserstr. 15, 04318 Leipzig, Germany
A room temperature wafer bonding process without applying external
pressure based on low energy hydrogen ion beam (300 eV) surface cleaning
has been studied for GaAs and other III-V-semiconductors. Successful
bonding has also been performed between III-V-wafers and Si or Ge, respectively.
X-ray photoelectron spectroscopy, atomic force microscopy,
ultrasonic microscopy, HR-TEM cross section, photoluminescence and
electrical characterization and post-processing steps were performed to
evaluate the ion beam treated surfaces and the formed bonded interfaces.
HL 44.65 Do 16:30 Poster A
Inhomogeneities in Au:GaAs(110) Schottky Barriers Studied
with Cross-sectional Scanning Tunneling Spectroscopy —
T.C.G. Reusch, •M. Wenderoth, and R. G. Ulbrich — IV.
Physikalisches Institut, Universität Göttingen, D-37077 Göttingen
Inhomogeneities in Au:GaAs(110) Schottky barriers have been investigated
with Cross-Sectional Scanning Tunnelling Spectroscopy. The influence
of metal-induced gap states and the electrostatic potential of
the depletion layer are visible in spatially resolved measurements. The
electrostatic potential of the depletion layer shifts the current onsets in
the tunneling spectra. By extracting the shift and from comparison with
simulations, we are able to map variations in the local electrostatic potential
in the depletion layer parallel and perpendicular to the interface
on a near-atomic scale. This information is complementary to Ballistic
Electron Emission Microscopy. The extracted SBH is in the range of 690
meV , which is somewhat smaller than the reported SBH of 950 meV for
Au:GaAs(110) contacts prepared under similar conditions. The observed
fluctuations of the potential at the interface of 2σ ≈ 60 meV are in good
accordance with reported values of BEEM investigations.
HL 44.66 Do 16:30 Poster A
Time-Resolved THz Spectroscopy Of Graphite Sheets —
•Tobias Kampfrath, Luca Perfetti, Christian Frischkorn,
and Martin Wolf — Fachbereich Physik der Freien Universität
Berlin, Arnimallee 14, 14195 Berlin
Pump-and-probe transmission measurements were performed with approximately
30 nm thick highly oriented pyrolitic graphite sheets at
room temperature in air. The sample was excited by a pump pulse centered
at 775 nm. A delayed probe pulse probed the linear optical re-
sponse parallel to the basal plane in a frequency range from about 10
to 30 THz. The field-resolved sampling of the probe pulses allows for
the determination of the temporally changing in-plane component of the
dielectric function. Data analysis shows that the transient signal decays
on timescales of 200 fs and 2 ps, respectively, which we attribute to
carrier relaxation.
HL 44.67 Do 16:30 Poster A
Optical properties of pulsed-laser deposited carbon films —
•P.V. Tolstykh 1 , S.P. Sernov 1 , V.K. Goncharov 2 , M.V. Puzyrou
2 , S. Shokhovets 3 , and G. Gobsch 3 — 1 BNTU Minsk, Skaryna
Prosp. 65, 220027 Minsk, Belarus — 2 Institute of Applied Physics Problems,
Kurchatov Str. 7, 220064 Minsk, Belarus — 3 Institute of Physics,
TU Ilmenau, PF 100565, 98684 Ilmenau, Germany
Optical properties (refractive index n and extinction coefficient k) in a
spectral region from 1.2 eV to 5.5 eV and the thickness d of thin carbon
films were determined by spectroscopic ellipsometry and optical transmission
measurements. The films were deposited on different substrates
(quartz, silicon and bronze) by sputtering of a graphite target placed in
a vacuum chamber (residual gas pressure was 1.3 mPa) using a Nd-glass
laser with wavelength and pulse duration of 1060 nm and 30 ns, respectively.
We studied the dependence of n, k and d on the laser pulse energy
(2 J to 8 J, 100 laser pulses) and the substrate temperature (295 K to
500 K) during the deposition. Further, we compare the properties of the
studied films with those of amorphous hydrogenated diamond-like and
arc-evaporated carbon films and discuss correlations between their optical,
structural and mechanical properties, as well as optimum conditions
for growing films suitable for different applications.
HL 44.68 Do 16:30 Poster A
Undercooling and Solidification of Liquid Silicon — •C. Panofen
1 , R.P. Liu 2 , G. Lohöfer 1 und D.H. Herlach 1 — 1 Institut für
Raumsimulation, DLR, Köln — 2 Yanshan University, Qinhuangdao, P.R.
China
Containerless processing by electromagnetic and electrostatic levitation
techniques was applied to undercool and solidify pure Si melts in a
high purity environment. Without surrounding crucible walls we achieved
large undercoolings of up to 330K below the melting point due to the
reduction of heterogeneous nucleation sites. A pyrometric sensor measured
the sample temperature contactlessly. We stimulated crystallization
by triggering with a silicon wafer at the desired undercooling. The velocity
of the solidification front as a function of undercooling was directly
determined by photo sensors and a high speed camera. We analyzed the
growth behavior within current theories of crystal growth in undercooled
melts. Special emphasis was placed to a microstructure transition from
faceted to dendritic growth. The results of the growth measurements
were correlated to microstructure formation upon undercooling prior to
solidification.
This work was supported by DFG under contract No. HE1601/16-1
and the Sino-German Science Center Beijing.
HL 44.69 Do 16:30 Poster A
Züchtung von Silizium-Nanowhiskern mittels Molekularstrahlepitaxie
(MBE) — •Luise Schubert, Peter Werner,
Nikolai Zakharov, Gerhard Gerth, Vadim Talalaev und
Ulrich Gösele — Max-Planck-Institut für Mikrostrukturphysik,
06120 Halle
Das Interesse an der Züchtung und Anwendung von Halbleiter-
Nanostrukturen ist in den vergangenen Jahren stark gestiegen. Wir
präsentieren die Möglichkeit, Si- Nanowhisker mittels Molekularstrahlepitaxie
(MBE) erfolgreich herzustellen. Vor der Si-Abscheidung wurden
die (111)-Silizium Substrate mit Gold bedampft, welches in Form von
Clustern auf der Substratoberfläche als Keime für das Whiskerwachstum
dient. Die bereits bekannte Wachstumstheorie, der sogenannte ”vaporliquid-solid”-
Mechanismus (VLS), liegt in dieser Art der Herstellung in
einer abgewandelten Form vor. Die Strukturen wurden mittels SEM und
TEM analysiert. Dabei kann gezeigt werden, dass die Länge mit der Breite
der Whisker korreliert. Der modifizierte VLS-Wachstumsmechanismus
wird diskutiert.