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Atom-thin silicon
films for supercomputers
From the Science &
Technology Desk
Published 1/15/2002
5:09 PM
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TORONTO, Jan. 15 (UPI) --
Atomically thin layers of crystalline silicon called "quantum
wells" may help lead to hand-held supercomputers and a light-speed fast
Internet in future, scientists in Toronto say.
"This promises to
help take silicon to new applications beyond its current limitations, pushing
existing transistor technology to new possibilities for
microelectronics," said lead researcher Zhenghong Lu at the University
of Toronto.
A quantum well is made of
sandwiched layers of electrically insulating material and semiconductive
films, each only a few nanometers -- billionths of a meter -- thick. The
electrons packed together in the atomically thin semiconductor layers remain
confined by the insulating nanofilms, forcing the electrons to increase each
other's energy levels and emit bright light.
Quantum wells can
therefore prove invaluable in light-based electronics. Scientists predict
these simple devices will prove key components of many futuristic inventions,
such as microchips and computer networks that use lasers and optical fibers
to transmit data instead of electrical pulses and metal wires.
Growing the ultrathin
silicon-based quantum wells has proven very difficult. Quantum wells need
their semiconductive layers to be atomically wide -- only 3 nanometers or
less, a width more than 30,000 times thinner than a human hair.
Instead of growing thin
layers up from scratch, the scientists instead tried whittling thicker layers
down. The researchers grew crystalline, semiconductive layers of pure silicon
roughly 50 nanometers thick on 200 nanometer-wide wafers of silicon dioxide,
the same insulating material comprising sand. They then exposed the silicon
crystal film to ultraviolet light and ozone, which oxidizes the uppermost
2-atom-thick layer. The oxidized silicon was then stripped off by dipping it
in hydrofluoric acid.
By repeating this
process, they whittled the crystalline silicon down to a half-nanometer, only
2 or 3 atoms wide. What makes the silicon-based quantum wells especially
invaluable is the quality of light they emit.
"They emit infrared
light at wavelengths of 1.5 microns -- the wavelengths used in
telecommunications," Lu said in an interview with United Press
International. "No other quantum well system can do that."
Since the quantum wells
are so thin, scientists also hope they can exploit the quantum properties
matter displays on the atomic level to develop ultrafast transistors.
"When talking about
nanoelectronics, you can in theory get really fast, ultrafast computers --
handheld supercomputers," Lu said.
While it might take
anywhere from two to 10 years before practical benefits from the silicon
quantum wells became available, "this is a very good first step,"
said solid state physicist David Miller of Stanford University in California,
a leading expert in photonics.
Lu and his colleagues are
currently working on expanding their quantum well.
"We've just
demonstrated one quantum well so far -- stacking of multiple quantum wells,
which many devices may require, really will be the next challenge," Lu
said.
The researchers reported
their results in Applied Physics Letters.
(Reported by Charles Choi
in New York.)
Copyright
© 2001-2003 United Press International
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