ELFT HÍRADÓ

[HAJNAL Zoltán <hajnal AT mfa.kfki.hu>]

Dear Colleagues!

The next MFA Seminar is going to take place out of the normal schedule

***     Monday, 2007-03-19, 11:00

at the usual location

***     Conference Room of the MFA
***     (1st Floor, Bldg. 26, KFKI Campus, Csillebérc)

Our Guest Speaker is

***     Prof. Robert W. Collins
***     The University of Toledo, Ohio, USA
***     http://www.physics.utoledo.edu/~rcollins/collins.htm

Title and abstract of his talk:

***     Real time polarization spectroscopies:
***     applications in thin film growth and surfaces for photovoltaics

Photovoltaics (PV) technologies based on thin films of hydrogenated
amorphous silicon (a-Si:H) and polycrystalline cadmium telluride
(pc-CdTe) have met with considerable success over the past few years.
These thin film PV devices are deposited by chemical and physical vapor
deposition methods on low cost substrates. Optimized devices have become
increasingly complex, and in the case of a-Si:H technology include as
many as a dozen major layers and several minor layers, as well, designed
to capture a broad range of the solar spectrum. In addition,
post-deposition processing may be required, and in the case of pc-CdTe
this includes a critical anneal under CdCl2 vapor. For a Si:H-based PV,
in-situ real time polarization spectroscopies including spectroscopic
ellipsometry (SE) have played a key role in establishing principles that
guide the fabrication of the optimized devices that are being used
widely in research and production.
In this seminar, an overview will be provided of the useful information
that can be extracted from such polarization spectroscopies.
Multichannel optical instrumentation will be described that measure
polarization state changes occuring upon light reflection from materials
and devices. The focus is on instruments that can extract
characteristics including complex dielectric functions at high speed
over a wide spectral range for in-situ real time applications. One
application example to be described is the study of complex
optical anisotropy spectra for the surfaces of cubic crystalline
semiconductors that provide a fingerprint of the surfaces. A second
example involves device development in which the evolution of
nanocrystallites in amorphous silicon thin films is controlled for the
optimization of solar cells. In a final example, losses due to plasmon
resonances in Ag/ZnO reflector structures are analyzed to
identify approaches for efficiency enhancement in a second pass through
PV devices.

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We always welcome everyone interested!