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ACADEMIC
BACKGROUND
My background
is physics and materials science reinforced by computer
simulations and applied mathematics.
The major orientation of my R&D work has been on semiconductor
for photovoltaics and microelectronics, with emphasis on microscopic and nanoscale
electrical and optical characterization in connection with
structural analysis of defects and nano-features. I spent more than
a decade working on various applied photovoltaic projects, and another
decade on characterization, modeling and processing of ultra
high purity semiconductor materials for microelectronics and
photovoltaic materials.
Research HISTORY
I started my
research with fabrication and characterization of II-VI
solar cells, then
I focused
on silicon material
properties and photovoltaic devices. This occurred at IMEC,1
during my PhD preparation. Then
I cooperated with Helios Technology,2
Pragma,3 and more recently, while at NCSU,4 with NREL,5
BP Solar,6 and Astropower7 on
photovoltaics and many other microelectronics and silicon companies.
The major research themes that I have worked on are:
1-
Semiconductor device modeling and computer simulation (Nonlinear
modeling of current-voltage characteristic of solar cells, Impedance
Characteristics of solar cells, Quantum Efficiency, Light Beam
Induced Current, material optical parameters by ellipsometry,
differential contrast imaging, Confocal Microscopy of etched
polycrystalline silicon, light scattering modeling by Ray Tracing
technique,...
2- Modeling
and computer simulation of point defect clustering, defect
nucleation, continuum modeling of oxygen precipitation in silicon
wafers
3-
Modeling and computer simulation of early stage point defect
formation and clustering in silicon during crystal growth, starting from melting
point.
4-
MeV ion
implantation and impurity gettering with Micron Technology Inc.8
5- Improvement
of Aspen Rapid Thermal Processing tool used in advanced microelectronic device fabrication,
300mm technology, in a joint project with Mattson Technology Inc.9
The investigations were based on: (i) x-ray topography (XRT) and TEM for analyzing process
induced slips and dislocations in silicon wafers, and (ii) non
invasive microwave Photo-Conductance Decay (mPCD) for charge carrier lifetime mapping,
in combination with XRT for detection of ultra low contamination
levels. In furtherance of the analysis of these defects, I have used
FTIR, and DLTS for impurity assessment and Raman scattering
spectroscopy for local strain detection at wafer contact points.
Under the same
joint-project I have analyzed (i) the dynamics of RTP
silicides by mapping the sheet resistance and by modeling
the temperature distribution and time profiles, and (ii) RTP of ultra
shallow junctions using high precision spreading resistance depth profiling.
6-
Early work on Injection Level
Spectroscopy for identification of impurities (at ultra low level) in semiconductors.
This technique, which is an extension of mPCD, was
intended to map and identify process induced contamination.
Contaminant are introduced at ultra low levels (1E10 cm-3)
in the ultra high purity silicon wafers.
7-
Low level nitrogen doping of ultra
high purity CZ and FZ silicon. Nitrogen appeared to be extremely useful for
nanoscale defect engineering and for controlling mechanical and
electrical properties of silicon. Extensive nanoscale defect
characterization based on HRTEM,
Z-contrast and EELS. This
analysis is supported by multi-scale modeling. Additionnally, Near Field Optical
Imaging was conducted.
8-
Strained silicon on graded
ultra thin SiGe heterostructures for nanoscale electronics. This
interesting subject is a hot topic industry,
9-
Modeling defect nucleation and growth
in ultra high purity silicon, and
10-
High Performance Computing for
materials atomic engineering.
Current Research
Activity
The objective of my program is to fabricate and/or modify nano-materials
and create novel design suitable for nano-device fabrication,
particularly solar cells. The main thrust is towards the development
of new concepts for photovoltaic devices that do not necessarily
rely on conventional photon-hole pair conversion mechanism. This
research utilizes multi-scale and multi-phenomena
modeling of materials and uses features and nanoscale
properties of materials.
Materials of
interest for my research are: silicon for nanotechnology, ultra-thin SiGe films, and carbon materials
(including diamond and nanotubes intended for Photovoltaic
applications).
Suitable analytical techniques that I use are Synchrotron x-ray Probe,
Synchrotron High Resolution FTIR, Spectroscopic Ellipsometry, Raman
Scattering, Photoluminescence Spectroscopy, Near Field Optical Probe,
and HRTEM coupled with Z-contrast and EELS for measuring nanoscale properties
and modification of nanoscale features. Another research area of
interest is Nano-optoelectronic materials and devices such as CNT
based sensors, bio-physics of pertinent materials, nanoscale optical methods to analyze local conformal changes of
molecules.
TEACHING
Past and present taught courses include: general physics, microwaves, optoelectronic, photovoltaic
materials and devices, and defects in semiconductors. Presently, my teaching
program is
being reoriented toward nanoscience, nanotechnology,
and
photovoltaics..
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Energy Bands of a 16,16 CNT
