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October 18, 2006

A 'Spin-Voltaic' Effect May Enable Silicon Spintronics

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 silicon. The difficulty is that silicon has an indirect band gap, Zutic said, which means that silicon cannot emit light efficiently.

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 electric energy.

"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.

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