Atom-thin silicon films for supercomputers

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.)

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