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Semiconductor injection laser
In 1962, Robert Hall created a
revolutionary type of laser that is still used in many of the electronic appliances
and communications systems that we use every day.
Robert N. Hall was born in New
Haven, Connecticut in 1919. After earning a BS in Physics from the California
Institute of Technology, he took a position with General
Electric at their Research and Development Center in Schenectady, New
York. There he contributed to the World War II effort by designing systems that
used continuous wave magnetrons to jam enemy radar. After the war, Hall returned
to CalTech to earn a PHD in Nuclear Physics (1948). He then returned to GE's
R&D Center, where he spent the rest of his professional career.
Hall's first major contribution
was to develop a technique for the purification of germanium, a metalloid element
then used to make transistors. A "chance observation" of the properties of pure,
crystalline germanium led him to discover alloyed p-n junctions and to create
the "p-i-n" diode. Hall's diode rectifier — basically, a semiconductor used
as a "rectifier," or AC to DC power converter — led him in turn to invent
a large area PIN rectifier which pioneered the technology that would later lead
to solid state "thyristors," which are still used as rectifiers today (with
silicon replacing germanium) in electric locomotives, high-voltage DC electrical
transmission and other fields.
In 1962, Hall became the envy of
his peers when he built the first semiconductor injection laser (patented in
1967 - # 2,994,018). He had recently attended a talk on highly emitting diodes,
and he realized that a semiconductor junction could support a simpler, more
direct type of laser. Hall's device, based on a specially designed p-n junction
semiconductor, allowed for highly efficient generation of coherent light from
a very compact source: the semiconductor crystal was only a 1/3 mm cube. The
electrons were injected directly by electric current into the junction, rather
than by an external, high-intensity light source.
Today, semiconductor lasers based
on Hall's original design are used in all CD and CD-ROM units, all laser printers,
some TV remote controls, and most fiberoptic communications systems.
By the end of the 1960s, Hall had
made a number of major advances in solid-state physics. In the 1970s, the energy
crisis inspired him to turn his attention to photovoltaics and solar cells.
Hall returned to work on germanium, which he was eventually credited with singlehandedly
making "the cleanest material on earth," and as such suitable for use in electron-hole
droplet experiments and in high quality energy spectrometers for nuclear particle
detectors.
Robert N. Hall retired from GE
in 1987, with 43 US patents to his credit. Over the past thirty-five years,
he has won a number of prestigious awards for his career of invention, including
induction into the National Inventors Hall
of Fame (1994). Since retiring, Hall has devoted himself to a number
of educational and community activities, including physics demonstrations for
Schenectady students, tutoring the learning disabled, and repairing tape recorders
for the Library of Congress Talking Books
Program.
Read our profile of Gordon Gould, inventor of "the" laser (1957)
Read our profile of Charles Hard Townes, inventor of the maser (1953)
[Dec. 1999]
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