GeAs (germanium and arsenic)
was the semiconductor substrate material of choice long before the III-V series
like GaN and GaAs came along. GeAs would be considered a III-IV semiconductor since
Ge is in group IV of the periodic
table (Ga is group III, As is group V). It is actually know simply as germanium.
1954, when this advertisement from Bell Telephone Laboratories appeared in Radio &
Television News magazine, was the same year that Texas Instruments (TI) introduced
the world's first commercially available
silicon (Si) transistor. The GeAs boule photo in the ad was printed
"life size," which makes it around 2" in diameter. Compare that to 12" diameter
wafers standard today for Si. Gallium nitride (GaN), a more exotic high frequency,
high temperature semiconductor compound, just recently grew (literally) beyond a
2" diameter boule size where it had been stuck for a decade. Individual device sizes
have decreased while wafer sizes have increased, so the number of devices per wafer
is way up and the cost per device is way down.
Bell Telephone Laboratories Ad
Germanium crystal grown at Bell Telephone
Laboratories (life size). It is sliced into hundreds of minute pieces to make Transistors.
Transistor action depends on the flow of positive current-carriers as well as electrons,
which are negative. Arsenic - a few parts per 100,000,000 - added to germanium produces
prescribed excess of electrons. With gallium added, positive carriers predominate.
Latest junction type Transistor uses both kinds of germanium in the form of a sandwich.
They Grew it for Transistors
Heart of a Transistor - Bell Telephone Laboratories' new pea-size amplifier -
is a tiny piece of germanium. If Transistors are to do their many jobs well, this
germanium must be of virtually perfect crystalline structure and uniform chemical
composition. But it doesn't come that way in nature.
So - Bell scientists devised a new way to grow the kind of crystals they need,
from a melt made of the natural product. By adding tiny amounts of special alloying
substances to the melt, they produce germanium that is precisely tailored for specific
uses in the telephone system.
This original technique is another example of the way Bell Laboratories makes
basic discoveries - in this case the Transistor itself - and then follows up with
practical ways to make them work for better telephone service.
Section of natural germanium, left, shows varying crystal structure. At right
is sectioned single crystal grown at Bell Laboratories.
Improving Telephone Service for America Provides Careers for Creative Men in
Scientific and Technical Fields
Bell Telephone Laboratories
Posted July 6, 2015