Their discovery, detailed this week in the advance online issue of the journal
Nature Photonics, follows the team's demonstration last summer of an integrated
circuit-an assembly of transistors that is the building block for all
electronic devices-capable of working at 1.5 degrees Kelvin above absolute
zero. That temperature, equivalent to minus 457 degrees Fahrenheit, is not only
less than the average temperature of deep space, but achievable only in special
research laboratories.
Now the scientists report that they have succeeded in building an integrated
circuit that operates at 125 degrees Kelvin, a temperature that while still
a chilly minus 234 degrees Fahrenheit, can be easily attained commercially with
liquid nitrogen, a substance that costs about as much per liter as gasoline.
"Our goal is to create efficient devices based on excitons that are operational
at room temperature and can replace electronic devices where a high interconnection
speed is important," said Leonid Butov, a professor of physics at UCSD,
who headed the research team. "We're still in an early stage of development.
Our team has only recently demonstrated the proof of principle for a transistor
based on excitons and research is in progress."
Excitons are pairs of negatively charged electrons and positively charged "holes"
that can be created by light in a semiconductor such as gallium arsenide. When
the electron and hole recombine, the exciton decays and releases its energy
as a flash of light.
The fact that excitons can be converted into light makes excitonic devices
faster and more efficient than conventional electronic devices with optical
interfaces, which use electrons for computation and must then convert them to
light for use in communications devices.
"Our transistors process signals using excitons, which like electrons
can be controlled with electrical voltages, but unlike electrons transform into
photons at the output of the circuit," Butov said. "This direct coupling
of excitons to photons allows us to link computation and communication."
Other members of the team involved in the discovery were physicists Gabriele
Grosso, Joe Graves, Aaron Hammack and Alex High at UC San Diego, and materials
scientists Micah Hanson and Arthur Gossard at UC Santa Barbara.
Their research was supported by the Army Research Office, the Department of
Energy and the National Science Foundation.
Posted September 27th, 2009
