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New transistor laser could lead to faster signal processing - incorporating quantum wells...

New transistor laser could lead to faster signal processing - incorporating quantum wells... - Physics Forum

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Old 11-17-2004, 06:53 PM
Ken Kubos
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Default New transistor laser could lead to faster signal processing - incorporating quantum wells...



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New transistor laser could lead to faster signal processing
November 15, 2004


Researchers at the University of Illinois at Urbana-Champaign have
demonstrated the laser operation of a heterojunction bipolar light-emitting
transistor. The scientists describe the fabrication and operation of their
transistor laser in the Nov. 15 issue of the journal Applied Physics
Letters.

Image: The transistor laser light beam with a infrared wavelength labeled
"hv" at the top is captured by CCD camera. The contact probes (dark shadow)
on the Emitter, Base and Collector. (Courtesy Milton Feng/Nick Holonyak)

"By incorporating quantum wells into the active region of a light-emitting
transistor, we have enhanced the electrical and optical properties, making
possible stimulated emission and transistor laser operation," said Nick
Holonyak Jr., a John Bardeen Professor of Electrical and Computer
Engineering and Physics at Illinois.

The same principle making possible the transistor - negative and positive
charge annihilation in the active region (the source of one of the
transistor's three currents) - has been extended and employed to make a
transistor laser, he said. Holonyak invented the first practical
light-emitting diode and the first semiconductor laser to operate in the
visible spectrum.

Unlike a light-emitting diode, which sends out broadband, incoherent light,
the transistor laser emits a narrow, coherent beam. Modulated at transistor
speeds, the laser beam could be sent through an optical fiber as a
high-speed signal.

"This is a true, three-terminal laser, with an electrical input, electrical
output and an optical output, not to mention a coherent optical output,"
said Milton Feng, the Holonyak Professor of Electrical and Computer
Engineering at Illinois. "It is a device that operates simultaneously as a
laser and as a transistor." Feng is credited with creating the world's
fastest bipolar transistor, a device that operates at a frequency of 509
gigahertz.

At laser threshold - where the light changes from spontaneous emission to
stimulated emission - the transistor gain decreases sharply, but still
supports three-port operation, Feng said. "The electrical signal goes down,
but the optical signal goes up."

Earlier this year, Feng and Holonyak reported their discovery of a
three-port, light-emitting transistor. Building upon that work, the
researchers fabricated the transistor laser in the university's Micro and
Nanotechnology Laboratory. Unlike traditional transistors, which are built
from silicon and germanium, the transistor laser is made from indium gallium
phosphide, gallium arsenide and indium gallium arsenide, but can employ
other materials in this family (the so-called III-V compounds).

"This work is still very much in its infancy," Holonyak said. "There is much
more to be learned, including how to separate and optimize the transistor
laser output between electrical signals and light signals."

Down the road, ultra-fast transistor lasers could extend the modulation
bandwidth of a semiconductor light source from 20 gigahertz to more than 100
gigahertz. Used as optoelectronic interconnects, transistor lasers could
facilitate faster signal processing, higher speed devices and large-capacity
seamless communications, as well as a new generation of higher performance
electrical and optical integrated circuits.

Co-authors of the paper with Feng and Holonyak are postdoctoral research
associate Gabriel Walter and graduate research assistant Richard Chan. The
Defense Advanced Research Projects Agency funded the work.

Source: University of Illinois at Urbana-Champaign
--
Ken

"Buddhism elucidates why we are sentient."



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