Plenarvorträge - DPG-Tagungen

Halbleiterphysik Mittwoch
absorbers as compared to (112)-textured absorbers are due to a lower
electronic activity of the film’s GBs resulting in a lower recombination
of minority carriers at the GBs.
[1] M. A. Contreras et al., Prog. Photovolt. Res. Appl. 7 311 (1999).
[2] S. Chaisitsak et al., Jpn. J. Appl. Phys. 41 507 (2002).
HL 30.3 Mi 15:45 H14
Quasi-Fermi-Level-Splitting in Cu(In1−xGax)Se2 from 300K-
Photoluminescence — •Gottfried Heinrich Bauer 1 , Rudolf
Brüggemann 1 , and Stephane Vignoli 2 — 1 Institute of Physics,
Carl von Ossietzky University Oldenburg — 2 Lab. PMCN (CNRS)
University Claude Bernard Lyon1, France
The splitting of Quasi-Fermi levels in Cu(In1−xGax)Se2 prepared under
pilot line production conditions with final cell efficiencies of 15 % has
been studied with calibrated luminescence YPL at 300K and with AM1equivalent
photon fluxes. The PL data have been evaluated with respect
to the chemical potential of the electron-hole ensemble/quasi-Fermi level
splitting according to Planck’s generalized law for the emission of nonthermal
equilibrium radiation from matter [1]. We have separated the
Bose-Term of the luminescence by dividing the pl-yield by the absorptivity
A(ω) derived from transmission/reflection. The spectral absorption
of CIGS shows considerable subgap absorption in the entire regime of
composition indicating a substantial density of states located in the gap,
supported by recent photo capacitance experiments [2]. In comparison
to the shift of the band gap with Ga concentration YPL shifts in energy
only very weakly. Accordingly the energetic separation of the quasi-Fermi
levels at 300K, determining maximum Voc, only marginally increases.
[1] P. Würfel, Physics of Solar Cells Physics, Wiley, 2003
[2] J.T.Heath, J.D. Cohen et al., Appl. Phys. Lett. 80, 4540 (2002).
HL 30.4 Mi 16:00 H14
Quantitative Photoluminescence In a-Si:H/c-Si
Heterostructures- Determination Of Quasi-Fermi Level
Splitting — •Saioa Tardon, Rudolf Brüggemann, and
Gottfried H. Bauer — Institute of Physics, Carl von Ossietzky
University Oldenburg
Photoluminescence is broadly applied for probing the electronic structure
of materials and is mostly recorded in arbitrary units, whereas absolute
luminescence additionally yields the information on the quality
of the photoexcited state of matter. We consider the experimentally detected
luminescence as spectrally selective radiation from matter in thermal
non-equilibrium and describe the emitted spectral photon flux by
Planck’s generalised law. Via this approach the luminescence flux from
semiconductors is related to the chemical potential of the electron-holeensemble/splitting
of quasi-Fermi levels and also to the concentrations
of electrons/holes in the initial/final states of the radiative transitions.
We have applied these diagnostics to a-Si:H/c-Si heterostructures with
different emitter a-Si:H-layers and with various methods of c-Si surface
passivation. The magnitude of the quasi-Fermi level splitting will be used
to predict the maximum achievable open circuit voltage in the final de-
vices.
HL 31 Grenz- und Oberflächen
HL 30.5 Mi 16:15 H14
Structural, optical and electronic properties of Cu(In,Ga)S2
epitaxial layers and heterostructures on Si(111) — •Th. Hahn 1 ,
A. Chuvilin 1 , J. Cieslak 1 , A. Dietz 1 , J. Eberhardt 1 , R. Goldhahn
2 , M. Gossla 1 , F. Hudert 2 , U. Kaiser 1 , J. Kräusslich 3 , H.
Metzner 1 , U. Reislöhner 1 , H.-W. Schock 4 , S. Siebentritt 5 , W.
Witthuhn 1 , and F. Wunderlich 2 — 1 Friedrich-Schiller-Universität
Jena, Institut für Festkörperphysik, Max-Wien-Platz 1, 07743 Jena
— 2 Institut für Physik, TU Ilmenau, PF 100565, 98684 Ilmenau —
3 Friedrich-Schiller-Universität Jena, Institut für Optik und Quantenelektronik
Max-Wien-Platz 1, 07743 Jena — 4 Universität Stuttgart, Institut
für Physikalisches Elektronik, Pfaffenwaldring 47, 70569 Stuttgart
— 5 Hahn-Meitner-Institut, Abteilung Heterogene Materialsysteme,
Glienicker Str. 100, 14109 Berlin
Epitaxial thin films of the quasi-ternary chalcopyrite compound
CuIn1−xGaxS2 (0 < x < 1) (CIGS) were grown epitaxially on Si(111)
substrates using Molecular Beam Epitaxy (MBE). The samples were
characterized using X-Ray diffraction (XRD) in various geometries, High
Resolution Transmission Electron Microscopy (HRTEM), Rutherford
Backscattering Spectroscopy (RBS), and Photoreflection (PR).
The layers show a continuous variation of band gap, lattice constants,
growth mechanism, and the appearence of various metastable orderings
with x. First I(U)-characteristics of heteroepitaxial CIGS solar cells are
presented, which were processed in a standard process involving KCNetching,
chemical bath deposition of CdS, and a ZnO:Al window layer.
HL 30.6 Mi 16:30 H14
Einfluss von CrGa- und FeGa-Paaren in Ga-dotiertem
Czochralski Silicium auf die Lebensdauer der Minoritätsladungsträger
— •Svetlana Beljakowa 1 , Dieter Karg 1 ,
Gerhard Pensl 1 und Jan Schmidt 2 — 1 Lehrstuhl für Angewandte
Physik, Universität Erlangen-Nürnberg, Staudtstr. 7/A3, D-91058
Erlangen — 2 Institut für Solarenergieforschung Hameln-Emmerthal
(ISFH), Am Ohrberg 1, D-31860 Emmerthal
Ga-dotiertes Czochralski Silicium wurde mit Cr und Fe durch Implantation
bzw. Diffusion verunreinigt. Die Bildung und Vernichtung
der CrGa- und FeGa1-Paare wurde mit Deep Level Transient Spectroscopy
(DLTS) untersucht. Es wurden die Aktivierungsenergien für
die Bildung und Vernichtung des CrGa- bzw. FeGa1-Komplexes bestimmt.
Bei gleichen Temperaturen erfolgen Bildung und Dissoziation
des FeGa1-Komplexes schneller als die des CrGa-Komplexes. Die
Wirkung der CrGa- und FeGa1-Paare auf die Lebensdauer der Minoritätsladungsträger
wurde mittels Microwave-detected Photoconductance
Decay (MW-PCD) untersucht. Die Lebensdauermessungen haben gezeigt,
dass interstitielles Chrom im Gegensatz zu CrB-Paaren rekombinationsaktiver
als der CrGa-Komplex ist. Interstitielles Eisen dagegen
erweist sich als weniger rekombinationsaktiv als der FeGa1-Defekt.
Zeit: Mittwoch 16:45–18:15 Raum: H14
HL 31.1 Mi 16:45 H14
Theoretical description of the nonlinear optical properties
of semiconductor surfaces — •T. Meier 1 , M. Reichelt 1 , M.
Rohlfing 2 , C. Voelkmann 1 , U. Höfer 1 , and S.W. Koch 1 —
1 Fachbereich Physik und Wissenschaftliches Zentrum für Materialwissenschaften,
Philipps-Universität, Renthof 5, D-35032 Marburg —
2 School of Engineering and Science, International University Bremen,
P.O. Box 750 561, D-28725 Bremen
The description of the nonlinear optical properties of semiconductor
surfaces is discussed via two examples. First, a microscopic approach,
which uses quasiparticle wavefunctions and dispersions obtained from
ab-initio band-structure theory as an input for Bloch equations [1], is
presented. Using this method, excitonic effects in the linear absorption
spectra of the Si(111)-(2×1) surface are obtained and light-intensitydependent
absorption changes of the surface exciton are predicted.
Second, experiments studying the coherent optically induced dynamics
at a Si(001) surface via a five-wave mixing set-up using three ultrashort
laser pulses are analyzed using optical Bloch equations. The measurements
show an unexpected slow rise of the signal intensity as function
of a particular pulse delay which extends well beyond the pulse duration
[2]. This response can be described by considering rapid scattering of the
photoexcited carriers to other states.
[1] M. Reichelt, T. Meier, S.W. Koch, and M. Rohlfing, Phys. Rev. B 68,
045330 (2003).
[2] C. Voelkmann, M. Reichelt, T. Meier, S.W. Koch, and U. Höfer, submitted.
HL 31.2 Mi 17:00 H14
DLTS investigation of UHV bonded Si interfaces — •Alin Mihai
Fecioru, Stephan Senz, Roland Scholz, and Ulrich Goesele
— Max-Planck-Institut für Mikrostrukturphysik, 06120 Halle
Si-Si interfaces were obtained by ultrahigh vacuum (UHV) wafer bonding.
The electrical properties were characterized by deep level transient
spectroscopy (DLTS) measurements correlated with temperature dependent
current-voltage (I-V) measurements.
For a p-p interface a high density of defects was observed, indicated
by a peak in the DLTS spectrum correlated with a thermally active potential
barrier. Typical values of activation energy corresponding to the