Plenarvorträge - DPG-Tagungen

Halbleiterphysik Montag
tion in this material. Acknowledgement One of the authors (K. Wang)
would like to thank the Alexander von Humboldt Foundation for the
fellowship.
HL 12.54 Mo 16:30 Poster A
Controlled growth of zinc oxide nano-pillars with a vapor-solidliquid
process — •Anton Reiser, Andreas Ladenburger, Xinmin
Cao, Uwe Röder, Rolf Sauer, and Klaus Thonke — Abt.
Halbleiterphysik, Universität Ulm, D-89069 Ulm
We have produced ordered zinc oxide nano-pillars using a vapor-liquidsolid
process [1]. A-plane sapphire substrates were covered with regularly
arranged gold particles in different ways via self-organizing processes.
The gold particles act as catalysts in the high temperature growth of the
zinc oxide pillars. Depending on the process parameters we generated
pillars with diameters from 30 nm to 2 µm and heights from 500 nm to
several micrometers. The created nano-structures were investigated by
scanning electron microscopy, X-ray diffraction and photoluminescence
spectroscopy revealing excellent crystalline material quality.
[1] M. H. Huang et al, Science 292 (2001), 1897
HL 12.55 Mo 16:30 Poster A
Regular silicon nano-pillars with high aspect ratios etched via
self-organizing nano-porous polymer masks — •Andreas Ladenburger
1 , Anton Reiser 1 , Feng Yan 2 , Johannes Konle 1 , Werner
A. Goedel 2 , Rolf Sauer 1 , and Klaus Thonke 1 — 1 Abt. Halbleiterphysik,
Universität Ulm, D-89069 Ulm — 2 Abt. Organische Chemie III,
Universität Ulm, D-89069 Ulm
We have produced regular silicon pillars with high aspect ratios on the
nanometer scale. In the process, first a nano-porous membrane defined by
the imprints of self-organizing colloidal particles was created on a silicon
wafer. Due to the self-organization the nano-pores form an array with
hexagonal ordering. Then a gold film was deposited on the structure and
the polymer membrane was removed. The remaining regular pattern of
gold disks was used as a mask in a deep reactive ion etching process. The
produced nano-pillars are 1.4 µm high and they have diameters less than
200 nm. As a by-product in the creation of the gold mask we obtained a
regular gold grid, which can be applied as an optical short pass filter.
HL 12.56 Mo 16:30 Poster A
Conductance spectroscopy of an AFM-engraved quantum
point contact — •B. Harke 1 , C. Fricke 1 , F. Hohls 1 , R.
J. Haug 1 , D. Reuter 2 , and A. D. Wieck 2 — 1 Institut für
Festkörperphysik, Abteilung Nanostrukturen, Universität Hannover,
Appelstr. 2, 30167 Hannover, Germany — 2 Lehrstuhl für angewandte
Physik, Ruhr-Universität Bochum, 44780 Bochum, Germany
We used the mechanical Atomic Force Microscope (AFM) lithography
to write insulating trenches in a two dimensional electron gas (2DEG) realized
by a GaAs/AlGaAs-heterostructure. To get insulated areas in the
2DEG which is located about 50 nm below the surface we wrote 10 nm
deep lines to deplete the 2DEG underneath the trench. We achieved isolating
lines with a breakdown voltage of at least 20V. For this lithography
we used a diamond tip for precise structuring of a quantum point contact
with the width of 500nm. Our characterization measurements show
distinct quantization of the conductivity in dependence of gatevoltage as
expected. Furthermore we show conductance spectroscopy measurements
for different magnetic fields. We observe a pronounced 0.7 anomaly which
was analyzed in dependence of magnetic field up to 15 Tesla and temperature
between 1.5 K and 10 K.
HL 12.57 Mo 16:30 Poster A
The manipulation of the energy levels in InAs-quantum dots
by thermal treatment — •Victorina Stavarache, Dirk Reuter,
and Andreas Wieck — Lehrstuhl für Angewandte Festkörperphysik,
Ruhr-Universität Bochum, Bochum, Germany
We have investigated the effect of thermal treatment on QD samples
by photoluminiscence (PL) measurements. The sample structure contains
10 QD layers separated by 100nm GaAs. The QDs have been grown by
MBE on a semi-insulating GaAs(100) substrate. After growth, the 4x4
samples were cleaved and annealed for 30s at temperatures from 800 o C
to 960 o C using a rapid thermal annealing system. With increasing annealing
temperature, the PL peaks show a shift to smaller wavelength.
Simultaneously, the energy separation between adjacent peaks becomes
smaller. These observation point to an increase of the energy difference
between electron and hole levels (from E=1,054eV for unannealed sample
to E=1,389eV for an annealing temperature of 960 o C) whereas the
intersublevel spacing decreases (from ∆E=52,7meV for unannealed sample
to ∆E=17,3meV for an annealing temperature of 960 o C). We explain
this blueshift due to the diffusion of the Ga atoms into the QD and the
out diffusion of the In atoms from the QD during the thermal annealing
process.
HL 12.58 Mo 16:30 Poster A
Chemical Vapour Deposition of Silicon Nanowires — •Volker
Schmidt, Stephan Senz, and Ulrich Goesele — Max Planck Institut
für Mikrostrukturphysik, 06120 Halle
Silicon nanowires are synthesized by chemical vapour deposition in
ultra high vacuum environment via the vapour-liquid-solid growth mechanism.
For this process silane is used as the precursor gas and gold dots
act as catalysts. The diameter of a single nanowire is determined by the
size of the gold particle. We investigate by scanning electron microscopy
and transmission electron microscopy the quality of the epitaxial growth
of the nanowires on silicon substrates of different orientation ((100) and
(111)). The effects of substrate temperature and silane partial pressure
on the growth of the nanowires are analyzed. We also investigate the
influence of a 2.45 GHz microwave plasma on the synthesis of the silicon
nanowires. The minimum substrate temperature is reduced and some of
the nanowires change their growth direction.
HL 12.59 Mo 16:30 Poster A
Investigation of Experimentally Observed InAs Quantum Dots
with an Analytical Bond-Order Potential — •Thomas Hammerschmidt
and Peter Kratzer — Fritz-Haber-Institut der Max-Planck-
Gesellschaft, Faradayweg 4-6, 14195 Berlin
A thorough understanding of the experimentally observed shape of
InAs quantum dots (QD) calls for non-equilibrium simulations that take
kinetic growth-effects into account. The modeling of such effects requires
large system sizes and long simulation times.
We address this issue with a new analytical bond-order potential of
the Abell-Tersoff type for InGaAs that was derived from previously published
potentials. We optimized the new potential for reconstructions of
the GaAs (001) surface with preserving the previous adoptions to GaAs
bulk phases. Furthermore, we adjusted the potential to capture different
In and InAs bulk phases, as well as InAs surfaces, more accurately.
With the new potential we determined the potential energy surface
and various diffusion barriers on high-index surfaces and compare with
density functional calculations. Additionally we relaxed uncapped InAs
QD in different experimentally observed shapes and investigate strain
effects.
HL 12.60 Mo 16:30 Poster A
Resonant tunneling through self organized InAs Quantum
dots — •T. Lüdtke 1 , F. Hohls 1 , R. J. Haug 1 , and K. Pierz 2
— 1 Universität Hannover, Germany, Solid State Physics, Department
Nanostructures — 2 Physikalisch-Technische Bundesanstalt
Braunschweig
The aim of our work was to do electron transport measurements on
resonant tunnelling devices containing only a few Quantum Dots (QD).
The sample is an GaAs/AlAs/GaAs tunnelling diode containing one layer
and in another one a double layer of self-organized InAs QD’s (1.5 - 2
ML) embedded in the AlAs barrier which lies about 1µm above the top.
The diodes with dimension of a about 50µm down to a few micrometers
were defined by electron beam lithography (EBL). The interesting problem
of contacting the small diodes to a bonding wire was solved with a
polyimide (PI) layer surrounding the mesa. Then a hole above the diode
is defined by EBL, and wet etching through the PI layer gave the opportunity
to connect the diode to a top contact of about 80µm. Temperature
dependent characterization measurements down to 1.5 K as well as magnetic
field variations were realized to study Coulomb Blockade, tunnel
coupling in double QD’s and to calculate g-Factors.
HL 12.61 Mo 16:30 Poster A
Capacitance-voltage (CV) measurements on a InAs quantum
dot ensemble and on single InAs quantum dots embedded in a
GaAs matrix — •Heidemarie Schmidt 1 , Stefan Jaensch 1 , Gerald
Wagner 2 , and Marius Grundmann 1 — 1 Universität Leipzig,
Fakultät für Physik und Geowissenschaften — 2 Institut für Nichtklassische
Chemie an der Universität Leipzig
Using Stranski-Krastanov growth mode, self-assembled InAs quantum
dots (QD) have been incorporated at 485 ◦ C in n-type GaAs grown by
MBE on (100)-GaAs n + -substrates. A typical dot diameter of 11.4 ± 2