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Oral History – Robert Hall
(Continued)
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A chance observation while
measuring one of the aforementioned ingots led me to the concept of a PIN
rectifier and to the alloying method of producing PIN power devices. I proved these ideas out of converting
tens of KW of AC into DC in my lab, using water-cooled Ge diodes. The same principal was applied by others
using Si instead of Ge, and these are used today to power locomotives and
in HVDC power transmission terminals.
I made measurements of these PIN rectifiers over a wide range of
temperature and current to figure out how they worked. However, I was
unable to account for their characteristics using the accepted model for
electron-hole recombination as described by Shockley; there was a factor of
2 missing in the exponential.
Finally, I figured out that a two-step transition through a deep
level recombination center near the middle of the forbidden gap would
explain everything, including observations on minority carrier lifetimes
that I and others were measuring at the time. I reported this and the idea was picked up by Shockley and
Read at BTL who produced a much more extensive analysis of recombination. This mechanism is now known as “Shockley-Read-Hall”
(SRH) recombination (or sometimes HSR recombination, depending on who you
are talking with). Anyhow, it is fashionable to cite this reference when
reporting anything dealing with recombination, so it has had a lot of
mileage.
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Oral History – Robert Hall (Continued)
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In 1962 I heard a report of
intense and highly efficient infrared emission from GaAs junctions and
realized that these results suggested that a semiconductor laser might be
possible. I came up with a
structure that we could build and I thought might work and rounded up a
group with the necessary talents to tackle the job. We succeeded in demonstrating the first
semiconductor laser, which included Fabry-Perot mirrors. Simultaneously, IBM reported stimulated
emission with pronounced spectral narrowing, which was very close, and
resulted in laser patents for both organizations. The German courts only allow one inventor. I was invited to testify there, with the
result that we (GE) were awarded the invention. That was all very excited, with the results documented
elsewhere.
IN 1977, I began an
investigation of silicon photovoltaic technology. I was the principal Investigator in a JPL (DOE) sponsored
development program in Sheet Silicon Growth in 1976-1977 and was the inventor
of the “Polka-Dot Solar Cell”.
Following this, I resumed studies of hydrogen-related defect
complexes in germanium, working out the kinetics of hydrogen pairing with
silicon and oxygen, and of hydrogen molecule formation following a quench
from an elevated temperature.
More recently, I undertook a study of precipitate defects which form
during processing of silicon integrated circuits. Since retiring from GE in 1987, I have been engaged as a
consultant in several areas of semiconductor technology.
Go
To Hall Oral History, Page 3
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