Plenarvorträge - DPG-Tagungen

Halbleiterphysik Donnerstag
Bauelementen denkbar. Es ergibt sich die Frage der geeigneten Platzierung
dieser AlN-Schichten innerhalb einer Bauelement-Struktur, um
mit einer möglichst geringen Anzahl die Rissfreiheit der Struktur zu
gewährleisten. Wir haben die Abhängigkeit der Lumineszenzausbeute
von InGaN-Schichten von der Dicke und der Komposition einer über
einer AlN-Zwischenschicht gewachsenen AlGaN-Schicht untersucht. Bei
einer Schichtdicke von 100 nm GaN bricht die Lumineszenzintensität
HL 46 Hauptvortrag Hoenlein
gegenüber vergleichbaren Proben ein, die auf einem 900 nm dicken
GaN/AlGaN-Puffer ohne AlN-Zwischenschicht gewachsen wurden. Dagegen
erholt sich die Lumineszenzintensität der InGaN-Schicht wieder,
wenn auf die AlN-Schicht eine Kombination aus 200 nm AlGaN und 70
nm GaN abgeschieden wird. Als mögliche Ursachen dieser Abhängigkeit
werden piezoelektrische Effekte oder kristallographische Defekte vermutet.
Zeit: Freitag 10:15–11:00 Raum: H15
Hauptvortrag HL 46.1 Fr 10:15 H15
Carbon Nanotubes - A Successor to Silicon Technology? —
•Wolfgang Hoenlein, Franz Kreupl, Georg Duesberg, Andrew
Graham, Maik Liebau, Werner Pamler, Robert Seidel,
and Eugen Unger — Infineon Technologies AG, Corporate Research,
Otto-Hahn-Ring 6, D-81739 Muenchen
Carbon nanotubes (CNTs) are powerful candidates for both interconnects
and field-effect transistors with better performances than silicon
based devices. The CNTs can be selectively produced in microelectronics
compatible processes using catalyst mediated CVD growth. One promis-
HL 47 Quantendrähte und Korrelationseffekte
ing concept for the integration of CNT’s into the existing silicon technology
is the replacement of metal wires at places of critical current density.
The recent results from CNT field-effect transistor devices will be reviewed
and compared with state-of-the-art silicon devices. Further, ideal
and non-ideal CNT transistors have been simulated and their properties
compared with the expectations for the 2016 silicon transistor. Based
on this, a concept for a 3-dimensional CNT based technology will be
presented. We will also identify the key success factors of the silicon
technology and assess the emerging CNT technology with respect to the
mature silicon technology.
Zeit: Freitag 11:00–13:00 Raum: H15
HL 47.1 Fr 11:00 H15
Coulomb blockade and Non-Fermi-liquid behavior in quantum
dots — •Frithjof Anders 1 , Eran Lebanon 2 , and Avraham
Schiller 2 — 1 Insititut für Theoretische Physik, Universität Bremen,
Postfach 330 440, D-28334 Bremen — 2 Racah Institute of Physics, The
Hebrew University, Jerusalem 91904, Israel
The non-Fermi-liquid properties of an ultrasmall quantum dot coupled
to a lead and to a quantum box are investigated using a new variant of
Wilson’s numerical renormalization group. Below the charging energy of
the quantum box, a second screening channel is dynamically generated.
Tuning the ratio of the tunneling amplitudes to the lead and box, we
find a two-channel Kondo fixed point for arbitrary Coulomb repulsion on
the dot, proving that the two-channel Kondo effect is far more generic
to this setting than the original scenario of Oreg and Goldhaber-Gordon.
At T = 0, a step-like structure is found in the conductance of a twolead
setting, the height of which depends on the dot occupancy. The
temperature scale below which the two-channel Kondo effect sets in is
greatly enhanced away from the local-moment regime, making this effect
accessible in realistic devices.
HL 47.2 Fr 11:15 H15
Inducing field-free currents in mesoscopic rings — •Alex
Matos-Abiague and Jamal Berakdar — Max-Planck-Institut für
Mikrostrukturphysik, Weinberg 2, 06120 Halle, Germany
We show theoretically that a sequence of two orthogonal linearly polarized
half-cycle pulses applied to a mesoscopic ballistic ring may induce
a non-equilibrium current. The post-pulses (and therefore field-free) current
lasts as long as the coherence is preserved. The dependence of the
sign and amplitude of the current on the different system parameters is
studied. The possibility of experimentally detecting the post-pulse current
is also discussed.
HL 47.3 Fr 11:30 H15
High frequency measurements on an AFM-structured quantum
point contact — •C. Fricke 1 , J. Regul 1 , F. Hohls 1 , R. J. Haug 1 ,
D. Reuter 2 , and A. D. Wiek 2 — 1 Institut für Festkörperphysik,
Abteilung Nanostrukturen, Universität Hannover — 2 Lehrstuhl für
Angewandte Festkörperphysik, Ruhr-Universität Bochum, 44780
Bochum, Germany
We fabricated a single quantum point contact by Atomic Force Microscope
(AFM) lithography. We used a diamond tip for structuring
the two dimensional electron gas (2DEG) realized by a GaAs/AlGaAsheterostructure.
The 2DEG is about 50 nm below the surface. Isolated
areas were written by about 10 nm deep lines. The quantum point contact
was designed for high frequency measurements using a special scheme
with strip-lines to source and drain contact and with nonmetallic in-
plane-gates.
Our measurements show the frequency dependence of the imaginary part
of the complex admittance between 100 and 400 MHz. Therefore a very
accurate measurement of the phase was necessary. The real part of the
admittance shows a good agreement with DC characterization. For the
imaginary part we observe a linear frequency dependence as expected by
theory.
HL 47.4 Fr 11:45 H15
Numerical calculation of electronic transport in molecular wires
— •Robert Dahlke and Ulrich Schollwöck — LMU – Sektion
Physik, Lehrstuhl von Delft, Theresienstr. 37, 80333 München
We present a numerical method for the calculation of electronic transport
through molecular systems. It combines quantum chemistry with a
scattering matrix approach to calculate a bias dependent transmission
function. The current is obtained by use of the Landauer formula. The
method can be used for STM-image calculations and can also be applied
for studying transport properties of molecular wires. We present results
for current/voltage calculations of self-assembled mono-layers of (1,4)phenylene
diisocyanide molecules attached to gold leads and compare
them to experimental data.
HL 47.5 Fr 12:00 H15
Spin-charge separation in one-dimensional quantum dots: nonlinear
transport and Negative Differential Conductance — •Fabio
Cavaliere 1,2 , Alessandro Braggio 2 , Juergen Stockburger 3 ,
Maura Sassetti 2 und Bernhard Kramer 1 — 1 I. Institut für Theoretische
Physik, Universität Hamburg, Hamburg — 2 Dipartimento di Fisica,
INFM-Lamia, Università di Genova, Genova, Italy — 3 II. Institut
für Theoretische Physik, universität Stuttgart, Stuttgart
The study and control of the spin degree of freedom is nowadays the
subject of many theoretical as well as experimental investigations. In few
electrons quantum dots, the spin selection rules are considered the cause
of the spin-blockade phenomenon [1] that leads to negative differential
conductance (NDC). In the present work [2] we find that in 1D quantum
dots the spin selection rules alone are not sufficient to give rise to NDC.
On the contrary, in the framework of the Luttinger liquid theory we find
that the separation of charge and spin degrees of freedom is responsible
for the emergence of NDC in quantum dots with asymmetric barriers.
The NDC phenomenon is related to the occupation of states with spin
higher than the one in the ground state, therefore the effect of spin-flip
relaxation processes is analyzed.
[1] D. Weinmann, et al. Phys. Rev. Lett 74, 984 (1995)
[2] F. Cavaliere et al. Submitted to Phys. Rev. Lett.