BUFFALO, N.Y. -- Can conventional semiconductors learn new
Igor Zutic is betting that they can.
Zutic, a University at Buffalo theoretical physicist and the
recipient of a prestigious National Science Foundation CAREER
Award, is finding ways to introduce spintronic properties and a
phenomenon called spin injection into silicon.
"For information processing and advanced logic operations, it
would be particularly desirable to integrate seamlessly magnetic
materials with silicon," said Zutic, Ph.D., assistant professor of
physics in the UB College of Arts and Sciences. "Rather than
displace all that we've learned about silicon through the decades,
my work tries to build on it."
Zutic's proposal for spin injection and detection in silicon was
published in July in Physical Review Letters with collaborators
Jaroslav Fabian of the University of Regensburg and Steven Erwin at
the Naval Research Laboratory.
Now, the October issue of Nature Materials is publishing Zutic's
"News & Views" article on related experimental efforts to grow
junctions of ferromagnetic metals and silicon.
Modern information technology uses the charge of electrons to
process information and the spin of electrons to store data.
While charge-based electronics is centered around semiconductor
silicon chips, magnetic data storage (as in computer hard drives)
relies on magnetic metals. The two spin directions, "up" or "down,"
provide a way to encode ones and zeroes for storing data, Zutic
Research efforts that attempt to combine these two technologies,
called spin electronics or spintronics, promise low power/high
speed computers, which could be turned on instantly and require no
In addition to being abundant and inexpensive, Zutic explained,
silicon also has very favorable spin properties, which could enable
improved performance in proposed spin transistors.
But in contrast to extensive studies with several conventional
semiconductors, such as gallium arsenide and indium arsenide, which
can be made magnetic by adding magnetic impurities or by growing
them next to standard ferromagnets, no such advances have yet been
realized with silicon.
Currently, even basic spintronic elements, such as reliable spin
injection -- ensuring that electrons injected into silicon maintain
their spin -- and spin detection have yet to be demonstrated in
The difficulty is that silicon has an indirect band gap, Zutic
said, which means that silicon cannot emit light efficiently.
"Circularly polarized light is the smoking gun that confirms the
presence of injected spin," he said. "That means, unfortunately,
that neat tricks of injecting or detecting spin optically, often
used at UB, are not directly applicable to silicon."
Zutic published an extensive discussion of these challenges in a
paper in Reviews of Modern Physics in 2004 that since has received
more than 500 citations.
It may now be possible to overcome this hurdle, he said, with a
phenomenon he has named the spin-voltaic effect, a spin analog of
the photovoltaic effect used in solar cells to convert light into
"In the spin-voltaic effect, an injected spin produces an
electrical signal due to its proximity with a magnetic region," he
said, "a signal that could be measurable even in an indirect band
gap material like silicon. Reversing the direction of injected spin
could lead to switching the direction of electrical current, which
can flow even if no electrical voltage has been applied.
"The spin-voltaic effect also can play an important role in
providing dynamically tunable current amplification in a novel
class of spin transistors, a building block for future spin-logic
applications," he said.
Recent work by Zutic's collaborators at the Tokyo Institute of
Technology has demonstrated for the first time the spin-voltaic
effect in direct band-gap semiconductors.
During a visit to Japan in August, Zutic continued his
collaboration with this group on efforts to detect this effect in
silicon. Scientists at the University of Tohoku in Sendai in Japan
are planning to conduct similar experiments.
Zutic's CAREER Award has been supporting his work since his
first year at UB. Such awards support the early career-development
activities of teacher-scholars "who are most likely to become the
academic leaders of the 21st century," according to the NSF.
The U.S. Office of Naval Research also funds his work.
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