Plenarvorträge - DPG-Tagungen

Oberflächenphysik Mittwoch
aufgelöste Photolumineszenz-Untersuchungen an Mehrfach-Quantentrog-
Strukturen aus Al0,35Ga0,65As/GaAs gezeigt, die unter Anwendung der
Schrägschlifftechnik präpariert wurden.
O 28.22 Mi 16:00 Bereich C
Structural, electronic and spin properties of In nanowires
on Si(111) surface — •Xóchitl López 1,2 , Anna Krivosheeva 1 ,
Friedhelm Bechstedt 1 , Jürgen Furtmüller 1 , and Andrey
Stekolnikov 1 — 1 Institut für Festkörpertheorie und Theoretische
Optik, FSU Jena, Max-Wien-Platz 1, 07743 Jena — 2 Instituto de Física,
Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla 72570,
México
In the last years the electronic and structural properties of the indiuminduced
(4×1), (4×2) and (8×2) surface reconstructions on Si(111) have
been intensively studied due to the potential applications on novel optoelectronics
devices. In this work the electronic structure calculations are
performed using density functional theory in the generalized-gradient approximation
and ultrasoft pseudopotentials. The atomic positions were
taken from a previous calculations [1], which are consistent with experimental
data. The electronic band structures with and without spin
polarization are calculated and discussed with respect to the metallic/insulating
character of the chains. Because the spin density distribution
on these systems might be important for their electronic properties,
we study the influence of the spin polarization on the atomic structure
and electronic states of the In nanowires on Si(111). Several initial spin
configurations are taken into account for all the surface reconstructions
in order to observe a magnetic ordering. We acknowledge the partial financial
support from CONACyT grants No.36651-E and 36764-E. [1] F.
Bechstedt et al., Phys Rev B 68, 1934XX (2003).
O 28.23 Mi 16:00 Bereich C
Ultrathin layers of Ag deposited on 4H-SiC(0001) — •Serguei
Soubatch and Ulrich Starke — Max-Planck-Institut für
Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart
Despite the significance of SiC for high-temperature and high-power
electronic devices based on metal/semiconductor interfaces, the initial
stages of metal layer formation on SiC surfaces still remain insufficiently
explored in comparison to well known metal/silicon heterointerfaces, such
as Ag on Si. We investigated the deposition of Ag on 4H-SiC(0001) using
quantitative low-energy electron diffraction (LEED). Ag layers of 0.2, 0.5
and 1 ML coverage were deposited on the clean (3×3) and ( √ 3× √ 3)R30 ◦
SiC(0001) surface phases. The structural development after room temperature
deposition as well as after annealing was studied. The (3×3)
phase is only marginally influenced by Ag deposition at room temperature.
Annealing leads to Ag diffusion and subsequent desorption without
a significant phase transformation. In case of the ( √ 3× √ 3)R30 ◦ phase
considerable changes can be monitored in the LEED intensities spectra
immediately after deposition. Here, structural changes are found during
annealing also, possibly caused by Ag diffusion. In both cases the original
surface phases reappear after Ag desorption.
O 28.24 Mi 16:00 Bereich C
High temperature stable silicide contacts on the nanometer
scale — •G. Gardinowski, C. Tegenkamp, T. Block, S. Vagt, V.
Zielasek, and H. Pfnür — Institut für Festkörperphysik, Universität
Hannover, Appelstrasse 2, 30167 Hannover
In order to characterize nanostructure electrically contacts are essential
to build a bridge between the macrospic and the mesoscopic world.
High temperature experiments with nanostructures on silicon substrates
are particularly interesting, but require contacts which can withstand
temperatures up to 1100 ◦ C without changes in their chemical composition
and without interdiffusion at the contact area of the silicide and
the silicon. Using electron beam lithography different silicide contacts on
both Si(111) and Si(100) surfaces have been fabricated and tested. With
regard to the specific formation temperatures for silicides, mainly Mo,
Ta and Ti have been tested. All three silicides are stable up to at least
800 ◦ C. The metallic character of the silicides was tested by masurements
of the conductivity. However, for higher temperatures the decomposition
of MoSi2 and TaSi2 sets in leaving behind rough contact areas. Only the
TiSi2 silicide remains intact, as checked by µ–Auger spectroscopy. Furthermore,
after optimization of the lithography parameters, TiSi2 contact
pads with separation lengths of 200 nm were fabricated successfully, i.e.
after removing the native oxide from the silicon surface (with pads) by
a high temperature annealing step, perfect silicon was found in between
the contacts as seen by STM/SEM. The edges of the contacts are rather
sharp and well–defined. The transition area was determined to be around
1nm.
O 28.25 Mi 16:00 Bereich C
Direct evidence from FTIR for hydrogen incorporation into
the MOCVD-grown P-rich reconstructed InP(100) surface —
•Tobias Letzig, H.J. Schimper, Thomas Hannappel, and Frank
Willig — Hahn-Meitner-Institute, Glienicker Str. 100, 14109 Berlin,
Germany
Recently, the groups of Schmidt and Bechstedt have discussed several
different surface reconstructions for InP(100). Three of those have
been assigned to actually prepared surface reconstructions. In the case
of MOCVD growth the P-rich (2x1/2x2) surface is postulated to contain
hydrogen bonds that stabilize buckled P-P dimers. A P-rich surface with
a different reconstruction is formed via MBE growth in the absence of
hydrogen. The In-rich (2x4) reconstruction also does not contain any hydrogen
atoms. We present here experimental support for the postulated
hydrogen bonds on the surface of MOCVD grown P-rich (2x1/2x2) reconstructed
InP(100) in the form of FTIR spectra that were measured
in UHV. We made use of a patented contamination free transfer of the
sample from the MOCVD reactor into a mobile UHV chamber. FTIR
spectra will be presented for the as-grown surface and for the surface
after further exposure to hydrogen and deuterium.
O 28.26 Mi 16:00 Bereich C
RMS-roughness of Si from nm to mesoscopic scale — •Stefan
Schröder, Herbert Pfnür, and Martin Henzler — Institut für
Festkörperphysik, Appelstr.2 D-30167 Hannover,Germany
The International Technology Roadmap for Semiconductors (ITRS)
defines a decrease in surface roughness and an increase of the site planarity
on a nm scale as two of the requirements for starting materials
for industrial fabrication of next generations of silicon based micro- and
nanodevices. The rms-roughness on different length scales is the principal
property examined to verify the accomplishment of the goals set. We calculate
Power Spectral Densities to examine the decay of rms-roughness
on the length scales open to STM-measurements (nm to µm) and light
scattering methods (µm to mm) on standard wafers after annealing in
a hydrogen environment. The light scattering method allows the detection
and counting of numbers of particles per area, as demanded by the
ITRS, to make sure that improved flatness is not accompanied by an increase
in defect-density. In further experiments profiles of etched steps are
monitored to determine diffusion behaviour. We gratefully acknowledge
financial support by Wacker Siltronic GmbH.
O 28.27 Mi 16:00 Bereich C
Photoelektronenbeugung an der oxidierten 4H-SiC(0001) Oberfläche
— •M. Schürmann, S. Dreiner, U. Berges, M. Krause und
C. Westphal — Universität Dortmund, Experimentelle Physik I, 44221
Dortmund
SiC ist ein Halbleitermaterial mit großer Bandlücke. Aufgrund seiner
Eigenschaften ist es hervorragend geeignet zur Herstellung von Halbleiterbauelementen,
die bei hohen Temperaturen, mit hohen Strömen
und hohen Frequenzen betrieben werden können. In diesem Zusammenhang
gewinnt auch die Kenntnis über die Struktur an der SiO2/SiC-
Grenzfläche an Bedeutung. In einer Photoelektronenbeugungsuntersuchung
wurden Beugungsmuster an einer oxidierten 4H-SiC(0001) Oberfläche
aufgenommen. Am U41-PGM Meßplatz bei BESSY II stand Synchrotonstrahlung
mit hohem Photonenfluß und guter Energieauflösung
zur Verfügung. Dadurch war es möglich die einzelnen, chemisch verschobenen
Komponenten in den XPS-Spektren aufzulösen und unterschiedliche
Beugungsmuster aufgrund der unterschiedlichen lokalen Umgebung
der Emitter zu erhalten. Ein Vergleich mit Simulationsrechnungen
gibt Aufschluß über ihren Ursprung und die atomare Struktur in der
SiO2/SiC-Grenzfläche.
O 28.28 Mi 16:00 Bereich C
Si2p-Photoemissionsspektroskopie an der SiO2/Si(100)-
Grenzfläche — •S. Dreiner, M. Schürmann, M. Krause, U.
Berges und C. Westphal — Universität Dortmund, Experimentelle
Physik I, 44221 Dortmund
Die SiO2/Si Grenzfläche spielt eine wichtige Rolle in der modernen
Halbleiterindustrie. Ein genaues Verständnis der Grenzschichtstruktur
kann zur Verbesserung der Qualität von Halbleiterbauelementen beitragen.
Die untersuchten SiO2/Si(100) Schichten mit einer Dicke von weni-