Plenarvorträge - DPG-Tagungen

Halbleiterphysik Mittwoch
Efficient electroluminescence (EL) was observed from silicon pn diodes
prepared by boron implantation [1]. The temperature dependences of the
EL intensity are strongly related to the boron implantation doses, the
creation of excess defects and the injection current. Effective suppression
of the electron-hole recombination through non-radiative channels is observed
at a high dose boron implantation (larger than 1×10 15 cm −2 ) or
at a high current injection. The dependences of the EL intensity on the
injection current at different temperatures can be well calculated with
a rate equation model. The theoretical calculations indicate that bound
excitons, which are responsible for the increase of the band-edge emission
at elevated temperatures, have a much higher thermal emission rate as
compared to the recombination rate in the diodes implanted with a high
boron dose.
[1] J.M. Sun et al., Appl. Phys. Lett. 83, 3885 (2003).
HL 28.7 Mi 16:45 H17
Breitband-Emission und geringe Absorption in Microdisks mit
AlGaAs-Quantenfilmen — •T. Kipp, K. Petter, Ch. Heyn, D.
Heitmann und C. Schüller — Institut für Angewandte Physik und
Zentrum für Mikrostrukturforschung, Universität Hamburg
Mittels holographischer Lithographie, reaktivem Ionenätzen und einem
selektiven nass-chemischen Ätzverfahren wurden großflächige Arrays von
Microdisks mit eingebetteten Al0.2Ga0.8As/Al0.4Ga0.6As-Quantenfilmen
aus einer mittels Molekularstrahlepitaxie gewachsenen Halbleiterschichtstruktur
hergestellt [1]. Wir beobachten in Mikro-Photolumineszenz-
Messungen an einzelnen dieser Microdisks über 20 Whispering-Gallery-
Modes in einem bemerkenswert breiten Energiebereich von über 250
meV. Die Spektren unterscheiden sich damit deutlich von den bislang publizierten
Spektren für Quantenfilm-Microdisks, in denen typischerweise
nur ein bis zwei optische Moden auftreten [2], und ähneln eher Microdisks
mit eingebetteten selbstorganisiert gewachsenen Quantenpunkten
[3]. Aus unseren Experimenten schließen wir, dass an Störstellen gebundene
Zustände unterhalb der Energie freier Elektron-Loch-Paare innerhalb
der ternären Quantenfilme zu einem effizienten, breitbandingen internen
Emitter mit geringer Absorption führen.
Diese Arbeit wird von der DFG im Rahmen des SFB 508 und dem
Graduiertenkolleg ” Felder und lokalisierte Atome“ gefördert.
[1] K. Petter et al., Appl. Phys. Lett. 81, 592 (2002)
[2] S. L. McCall et al., Appl. Phys. Lett. 60, 289 (1992)
[3] B. Gayral et al., Appl. Phys. Lett. 75, 1908 (1999)
HL 28.8 Mi 17:00 H17
Photonic Band Gap Structures in the 25-60 GHz Range —
•Rados Gajic 1,2 , Ronald Meisels 1 , Fridemar Kuchar 1 , Jelena
Radovanovic 2 , Alexander Woess 3 , and Juergen Stampfl 4
— 1 Insitut fuer Physik, Montanuniversitaet Leoben, Oesterreich
— 2 Institute of Physics, P:O. Box 68, 11080 Belgrade, Serbia and
Montenegro — 3 Erich Schmidt Institut fuer Materialwissenschaften,
Oesterreichische Akademie der Wissenschaften, Leoben, Oesterreich
— 4 Institut fuer Werkstoffkunde und Materialpruefung, TU Wien,
Oesterreich
In this work we present experimental and numerical results on 2D and
3D photonic band gap structures (PBGS) in the frequency range between
HL 29 Spinabhängiger Transport I
25 and 60 GHz (millimeter waves). For the fabrication of the PBGS we
used commercially available alumina rods as well as a rapid prototyping
method. In the 3D case, the woodpile (layer-by-layer) structure was
investigated in order to find the optimal configuration regarding the gapto-midgap
ratio. We also demonstrated the presence of higher in our 2D
and 3D PBGS. We compared these experimental findings with numerical
calculations based on the transfer matrix method. It was found that a
slight change of the cubic fcc structure towards the tetragonal fct geometry
yields increased gap-to-midgap ratios (higher than 30 procent). This
work is supported by Austrian FWF project No. 15513 and the Serbian
Ministry of Science project No. 1469.
HL 28.9 Mi 17:15 H17
Impact of oxidation on InN layer properties investigated by
Spectroscopic Ellipsometry — •Tobias L. Schenk, Torsten
Schmidtling, Massimo Drago, Christoph Cobet, and Wolfgang
Richter — TU Berlin, PN6-1, Hardenbergstr. 36, 10623 Berlin
MOVPE grown InN films on sapphire by Spectroscopic Ellipsometry
(SE) in the range of 0.8-6.5eV have been investigated. The observed
range is extended to include the newly assumed band gap position of
about 0.9eV. The exact position is indeed unknown yet, since oxidation,
poor layer quality, and high number of intrinsic defects influence the optical
properties. An important fact seems to be the oxidation of the still
defective layers. Therefore MOVPE grown layers in different grades of
oxidation are prepared and studied under controlled conditions and also
compared to MBE grown and sputtered ones. We find a strong dependence
of the band gap position on the oxidation state. This demonstrates
that oxidation is a critical factor contributing to the uncertainty of the
determination of the band gap value. Furthermore the oxidation influence
on the optical constants is evident in the whole spectral region leading
to a strong decrease in the dielectric response of the higher transitions.
HL 28.10 Mi 17:30 H17
MOVPE growth of InN layers: in-situ control of the growth
parameters by Spectroscopic Ellipsometry — •Massimo Drago,
Christoph Werner, Tobias L. Schenk, Torsten Schmidtling,
Udo W. Pohl, and Wolfgang Richter — TU Berlin, PN6-1, Hardenbergstr.
36, 10623 Berlin
The growth of indium nitride by MOVPE is a challenging issue, particularly
due to the low enthalpy of formation and the large lattice mismatch
to available substrates, like e.g. sapphire. At present, the quality of
MOVPE samples is not yet comparable with the MBE ones, and further
optimisation is necessary. In-situ Spectroscopic Ellipsometry (SE) control
turned up to be an excellent tool to understand the critical processes
occurring during growth [1]. It is shown how in-situ SE can monitor the
effects of changes in temperature, total pressure and V/III ratio. The
ellipsometric parameters measured and the effective dielectric function
behaviour are effectively related to growth rate, surface smoothening and
roughening. Improved quality layers obtained through optimised growth
parameters are characterised through SEM and XRD. [1] M. Drago, T.
Schmidtling, U. W. Pohl, S. Peters and W. Richter; phys. stat. sol. (c),
1-4 (2003) / DOI 10.1002/pssc.200303429
Zeit: Mittwoch 15:15–18:15 Raum: H13
HL 29.1 Mi 15:15 H13
Dephasing in Rashba–Spin precession along mutli–channel
quantum wires and nanotubes — •Wolfgang Häusler —
Physikalisches Institut, Albert-Ludwigs-Universität, Hermann-Herder-
Str. 3, 79104 Freiburg
Coherent Rashba spin precession along interacting multi-mode quantum
channels is investigated, revisiting the theory of coupled Tomonaga-
Luttinger liquids, and extending the theory [1]. We identify susceptibilities
as the key-parameters to govern all low energy properties, also in
spin sector. In semiconducting quantum wires spins of different transport
channels are found to dephase as a result of the interaction. This could
explain the experimental difficulty to realize the Datta Das transistor. In
single wall carbon nanotubes, on the other hand, interactions are found
to suppress dephasing between the two flavor modes at small doping.
[1] W. Häusler, Phys. Rev. B 63, 121310 (2001)
HL 29.2 Mi 15:30 H13
Spin Polarization of Two-Dimensional Hole Systems — •R. Winkler
1 , E. Tutuc 2 , S. Melinte 2 , M. Shayegan 2 , D. Wasserman 2 ,
and S. A. Lyon 2 — 1 Institut für Festkörperphysik, Abt. Nanostrukturen,
Universität Hannover — 2 Department of Electrical Engineering,
Princeton University
Hole systems are conceptually different from electron systems due to
the fact that hole states have an effective spin j = 3/2. Subband quantization
in quasi two-dimensional (2D) systems yields a quantization of
angular momentum with z component of angular momentum m = ±3/2
for the heavy hole (HH) states and m = ±1/2 for the light hole (LH)
states. The quantization axis of angular momentum that is enforced by
HH-LH splitting is pointing perpendicular to the plane of the quasi 2D
system. On the other hand, in general the effective Hamiltonians for
B = 0 spin splitting and Zeeman splitting in an in-plane magnetic field
B > 0 tend to orient the spin vector parallel to the plane of the quasi