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Research
In
our laboratory, we use molecular beam epitaxy (MBE) to enable the
growth of
extremely precise, low defect materials with unique properties. An
integrated, three-chamber MBE
deposition system has been established and linked together with a UHV
backbone transfer system. In the Group IV chamber, we grow Si and Ge
epitaxial films, SiGe compounds, and strained heterostructures.
The III-V chamber has recently been upgraded with new hardware
and includes the capability of growing any combination of high-quality
In, Ga, As, P, Al, and N compounds as well as in-situ H-cleaning and C,
Be, and Si doping. The II-VI chamber can produce a number of films
including CdTe, ZnS, and Be and Se compounds. Each chamber is
fully controlled by computer and operates at a base pressure in the 10-11
mbar range. In-situ analytical tools allow us to assess growth
quality in real-time and are coupled with the university's extensive
ex-situ characterization facilities. These MBE capabilities allow
us to study
materials that are important for a number of applications such as:
- Photovoltaics: We
are studying the nucleation and growth of very low defect
multi-junction solar cells. These junctions are grown using MBE to make
numerous III-V (GaAs, InGaP, etc) semiconductor materials with various
lattice structures and energy band gaps in an effort to improve the
efficiency of these types
of solar cells. Using growth techniques, such as metamorphic buffer
layers, our goal is to improve the efficiency of PV to a level that
would allow widespread terrestrial use. We also study other
unique solar cell structures (and LEDs) using quantum dots which allow
for the absorption of photons from a broader energy range. Thin
film II-VI materials such as CdTe are
also being investigated.
- Li-ion
Batteries: We
are investigating numerous aspects of Li-ion batteries for enhanced
energy storage. This includes solid electrolytes (LLTO), advanced
cathode materials (LiNiMnO2), next-generation anode
materials (Si nanotubes), and the associated solid-electrolyte
interphase (SEI). Using chemical synthesis methods and epitaxial
growth techniques, novel structures are formed that allow us to control
the Li+ reaction pathways in these materials. The
insight gained of the chemical bonding and transport in these materials
and interfaces are directly applied to full-cell batteries fabricated
in our lab for correlation to charge storage capabilities.
- III-V
Nanoelectronics: Using
our growth capabilities, we are developing and investigating a wide
range of III-V (as well as Ge and Si) semiconductor materials and
heterostructures for use in
low-power CMOS technologies. Collaborating
with many of the other research groups in MSEN and building on the
department’s reputation in this field, we are developing a
detailed understanding of these III-V systems to enable electronics to
maintain high-performance yet consume less energy.
We
have established collaborations
with other researchers in Materials Science, Physics, Electrical
Engineering,
and Chemistry. We work closely with
researchers at NIST and from other universities (for example NC State,
Purdue,
Dublin City University, and University College Cork), and we maintain
ongoing
projects and collaborations with U.S. Industries (Texas Instruments,
SRC, SEMATECH). Our goal is to develop a
fundamental
understanding of the issues associated with energy harvesting,
reduction, and
storage to significantly advance the scientific community, while
greatly contributing
to technological advances and environmental responsibility.
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