Wax nostalgic about and learn from the history of early electronics. See articles
from Popular Electronics,
published October 1954 - April 1985. All copyrights are hereby acknowledged.
Hmmmm... I never really thought about the transistor as a crystal amplifier
(a la the 'crystal detector'), but in fact it was fabricated
from a crystal of germanium with two 'cat whisker' wires pressing on its surface. Before the
transistor was the simple rectifier made of a crystal of selenium or even carborundum with
a point contact. Those were used for turning AC into DC and for detecting radio wave modulation
envelopes. For a really good synopsis of the early development path of semiconductors, read
this story from a 1968 edition of Popular Electronics that commemorated the 20th anniversary
of Bardeen, Shockley, and Brattain announcing their transistor. Having been written much closer
to the days of discovery, the story has not been filtered through as many writers' points
of view, and contains some information I'll bet you have never read before. E.g., did you
know that semiconductor dopants were originally referred to as adulterants? Did you know that
Shockley's early research was on field effect devices and, if successful, would had made FETs
the first forms of transistors rather than bipolar junction types? Did you know that the name
'transistor' (trans-resistor) was coined after the vacuum tube's amplification action called
'transconductance?' Read on for more.
The Quest for the Crystal That Amplifies
We call it a transistor - but 20 years ago it was and ugly duckling.
by Daniel M. Costigan
The birth of the transistor was not something that happened overnight. It marked the culmination
of many years of dreaming and searching, not only by scientists, but by a couple of generations
of quixotic tinkerers as well, seeking to extract from a tiny chunk of the mineral galena
some magical energy that might eliminate the need for power-consuming vacuum tubes in radio
receivers. Some of these experimenters actually produced crystal sets that could operate loudspeakers-at
low volumes - perpetually and without need for external power.
Sir Oliver Lodge (1851-1940) made many important contributions to wireless
transmission and reception, which led to UHF transmission techniques.
These devotees of the galena mystique thrived for some thirty years on trial-and-error
and wishful thinking. During this time, they were joined by a handful of scientists who worked
unnoticed behind the scenes, taking a more methodical approach to essentially the same goal.
The scientists were mostly engineers, metallurgists, and physicists who had been recruited
by industry - some of them from university faculties - to help seek new ways to improve the
efficiency of electric power and communications devices.
Finally, in the late 1940's, the quest for the crystal that amplifies ended in triumph
for a trio of distinguished industrial scientists. The year 1968 marks the 20th anniversary
of what has since become recognized as one of the most momentous events in the annals of electrical
How The Quest Began.
The primordial spark to which this quest can be traced occurred around the turn of the
century when the need for a practical rectifying device arose almost simultaneously in two
budding young industries: electric power, and radio.
In electric power, the advocates of alternating current had won their battle against the
d.c. interests and had begun to distribute a.c. power on a wide scale. This meant that some
kind of practical converter, other than a motor-generator, would be needed to permit the operation
of d.c. apparatus - battery chargers, electroplating equipment, telephonic devices, etc. -
on commercial a.c. power.
The rectifying properties of selenium had been known for nearly a century, but it wasn't
until 1924 that semiconductor rectifiers became commercially available. By the early thirties,
copper-oxide rectifiers had come into wide use as converters. Selenium, which had at first
proved unsatisfactory for use in power conversion, was gradually improved and eventually surpassed
copper-oxide in popularity.
The names Mott and Schottky are two that stand out in connection with the early evolution
of rectifier theory. Working independently of one another - Sir Nevill Mott in England and
W. Schottky in Germany - both men concluded that rectification took place in a thin electrical
barrier that formed at the junction of a metal contact and a semiconductor. Schottky called
this surface barrier an "inversion region" within the thickness of which a change of conductivity
took place. The theory was to play a prominent role in the reasoning that later led to the
invention of the transistor.
Radio's need was for a practical rectifying detector of received signals, and it arose
with the advent of voice transmission. In its embryonic stage (1894 to about 1906), a radio
receiver had at its heart a "coherer," in which metal filings clung together on exposure to
electromagnetic disturbances, thereby varying the current in a local battery circuit. The
disturbances were set up by a spark transmitter being turned on and off with a telegraph key.
First used by England's Sir Oliver Lodge in 1894, the coherer* had been
steadily improved in design and had reached a fairly high level of refinement by 1900 when
Professor Reginald Fessenden of the University of Pittsburgh succeeded in transmitting voice
on a continuous wave.
Professor Reginald Aubrey Fessenden (1866-1932). a pioneer in wireless
communication, was the first man to voice-modulate a continuous-wave carrier.
Radio suddenly found itself faced with much the same situation that had created the need
for rectifiers in the electrical industry. The transmitted radio wave became a "carrier,"
its cargo a modulation envelope that was electrically self-cancelling until the alternating
current could be made to flow in one direction only. Radio detection thus became a matter
Fessenden's first detector was an electrolytic device of his own design. It was highly
sensitive, but also critical and unreliable.
The first practical crystal detectors appeared in 1906. The one invented by G. W. Pickard
used silicon and featured a "catwhisker" (fine wire) contacting arrangement similar to that
suggested by a German experimenter named Braun some 30 years earlier. Another type, invented
by H. H. Dunwoody, an executive of the De Forest Wireless Company, used a small chunk of carborundum
clamped between two electrodes.
Vacuum Tubes and Diodes.
The crystal detector reigned supreme until the early twenties when the vacuum tube began
to make inroads. Silicon had proved to be the most stable crystal, but galena (lead sulphide)
was the most sensitive and therefore the most popular.
As in everything, however, it takes power to beget power; thus, there were the inevitable
"A" and "B" supplies wherever vacuum tubes were used. What's more, some of the power had to
be wasted in heating the tube filament - an unfortunate requisite that was to impose serious
restrictions on the tube's useful life and on the design of the tube-using equipment.
Crystal detectors needed no external power supply; they were simple and compact, and there
was no heat problem. But they couldn't amplify - at least not until a group of scientists
at a major industrial research laboratory had undertaken an intensive investigation into the
mysteries of solid-state semiconductors.
In 1934, the Bell Telephone Laboratories began to develop fixed semiconductor diodes for
use in microwave experiments. The earlier ones were silicon and germanium point-contact devices
resembling the "fixed" detectors that had been used in some crystal broadcast receivers. ("Point-contact"
is a sophisticated term for the old familiar catwhisker.) The more advanced junction diodes
were developed during and immediately following World War II.
A New Turn.
Walter H. Brattain had come to Bell Labs shortly after having received his Ph.D from the
University of Minnesota. His involvement during the thirties in the study of electrical conductivity
in semiconducting materials eventually brought him in contact with William Shockley, a brilliant
young Ph.D who joined the staff in 1936 and soon began to form some ideas of his own on the
potentials of semiconductors.
In that same year (1936), Dr. Mervyn Kelly was appointed Director of Research at Bell Labs,
and one of his first acts was to assemble a team of physicists to formally explore the behavior
of electrons in solids. Brattain and Shockley were among those selected.
Since the late thirties, Shockley had been entertaining the notion that a semiconductor
ought somehow to be able to amplify an electric current. His attempts to achieve "valve action"
in a copper-oxide device were interrupted by World War II. Immediately following the war,
he constructed a special device based on a scheme he had worked out on paper. But, as is so
often the case, what appeared workable on paper did not work in actuality.
Ironically, the device that had failed was the forerunner of the field-effect transistor
(FET), which was to re-emerge many years later to be heralded as one of the more important
advances in solid-state technology. Had Shockley's experiment been successful - if more had
been known about the characteristics of semiconductor materials - the development of solid-state
devices might have taken a completely different course.
It was about the time of Shockley's "field-effect" experiment that the Bell Labs team was
enhanced by the addition of a new member. He was John Bardeen, a 37-year-old theoretical physicist
and former university professor whom Shockley had personally recruited. During the preceding
decade, Bardeen had done extensive work in the field of electroconductivity in solids. The
fact that Shockley's experiment had not yielded the expected result interested Bardeen and
set him working on a theory to explain why.
Taking his cue from Mott and Schottky, Bardeen theorized that surplus electrons gathered
at the surface of a semiconductor and became immobilized so that, in effect, they acted as
a sort of barrier to externally applied currents. To test his "surface states" theory, he
and Brattain performed a series of interesting experiments.
At first they used a liquid electrolytic as a current-carrying medium between one side
of a power source and the surface of a piece of semiconducting silicon. They found that by
passing a current through the electrolyte, the surface charge on the silicon could be altered.
William Shockley, John Bardeen, and Walter H. Brattain, co-discoverers
of the transistor, received the 1956 Nobel Physics Award for their invention.
This led Brattain to suggest a slightly modified approach. Germanium was substituted for
silicon, and a thin layer of gold for the electrolyte as the special contacting interface.
Two currents were made to flow in opposite directions through the germanium, one between the
gold contact and a solid connection at the base of the material, and the other between the
base connection and a cat-whisker contacting the surface - near the gold contact. As had by
now been anticipated, varying the one current produced corresponding variations, but of greater
magnitude, in the other. Amplification had been achieved!
The technical explanation for the phenomenon was highly complex and dealt with such things
as atomic valences, "holes," "donors," and "defect conductivity." Stated simply, what had
happened was that the tiniest plus charge at one of the two contact points on the semiconductor
surface had drawn off enough of the material's surplus electrons to create "holes," which,
in turn, were attracted to the adjacent negative point and therefore functioned as vehicles
by which the lesser current could influence the greater one. In essence, then, the semiconductor
had become a variable resistance, enabling control of current flow in one circuit by varying
the current in another.
By the close of 1947, experiments had proved the new device capable of amplifying audio
frequency signals. Bardeen and Brattain quietly announced their discovery via a letter to
the editor of "The Physical Review," published in the July 15, 1948, issue.
The First Transistors.
The name transistor, by which the device was to become known, was suggested by another
Bell Labs physicist, John R. Pierce. Pierce observed that, where a vacuum tube amplified by
transconductance - the effect of the grid voltage on plate current - the new device did its
amplifying by what might more aptly be termed "trans-resistance." The name may also be thought
of as suggesting the transfer of signals through a varistor, a varistor being a semiconductor
diode whose electrical resistance decreases substantially with a moderate increase in applied
voltage. (Varistors are often used as buffers to protect delicate components from voltage
The first transistors produced in quantity in the laboratory contained a tiny chunk of
slightly impure germanium on which two "catwhiskers" converged, contacting the surface at
points less than a hair's breadth apart.
William Shockley, meanwhile, continued to pursue his own ideas on how best to make a semiconductor
amplify. His quest led to the invention, later in 1948, of the junction transistor in which
transistor action was achieved by the sandwiching together of p-type (electron deficiency)
and n-type (electron surplus) semiconductors. Shockley's design, although at first more difficult
to fabricate, proved more predictable in its properties and less fragile than its "point contact"
predecessor, and was therefore soon to supersede it. The junction transistor was introduced
early in 1951.
A major obstacle to mass production was the requirement that semiconductor materials contain
carefully controlled degrees of impurities to insure the proper electrical imbalance. This
meant starting with a nearly pure substance and then adding adulterants (such as arsenic or
gallium) by a carefully controlled doping process. The introduction of zone refining in 1955
was the first big breakthrough in high volume production of the basic materials.
In recognition of the magnitude of the revolution they had kindled, the transistor's trio
of inventors - Shockley, Brattain, and Bardeen - were awarded the 1956 Nobel Prize in Physics.
But, during the middle fifties, the widely acclaimed little device still suffered a number
of serious shortcomings. For one thing, it was critically temperature-sensitive and therefore
unable to handle power beyond a fraction of a watt. What's more, it was noisy and unstable,
had ridiculously low input impedance, and was a sluggish device whose switching speed and
frequency response left much to be desired.
These shortcomings, however, were gradually overcome as new manufacturing processes were
introduced and semiconductor materials with improved electrical characteristics were developed.
By the late fifties, the reliability of the device had already begun to exceed that of vacuum
The year 1957 was the best ever for the sale of vacuum tubes. Unit for unit, they were
still outselling transistors by thirteen to one. But the gap was rapidly narrowing, with the
turning point due in the early sixties. (In 1959, 77.5 million germanium transistors were
sold for a total of 151.8 million dollars, at an average price of $1.96 per unit. By 1966,
the picture was considerably changed: 368.7 million units were sold for a total of 164.5 million
dollars, an average price of 45 cents each!)
Further Improvements. New developments followed in rapid succession, and with them came
a whole new electronics vocabulary: p-type, n-type, bipolar, diffused junction, epitaxial
growth. The grown junction gave way to the alloy junction, which, along with the introduction
of the diffusion process, resulted in improved frequency response and switching speeds. It
was now feasible to use transistors in computers - a marriage which, in turn, was to enhance
the evolution of still faster and more reliable semiconductor devices.
The diffusion process also broke the transistor's power-handling and temperature barriers
by facilitating the use of silicon in place of germanium. Mesa, planar, and epitaxial devices
emerged as some of the more prominent offshoots of the diffusion technique.
The field-effect transistor, which had continued to lie dormant in the laboratories, seemed
to hold the key to some of the improvements still needed - higher input impedance, for example,
and lower levels of noise and distortion. Of all semiconductor devices, it came closest to
a vacuum tube in characteristics. But the electrical surface properties of the semiconductor
material used in its fabrication were critical, and it was not until recently that FET's finally
became competitive with other semiconductors.
Similarly, the unijunction transistor, with its single p-n junction, was originally developed
in the early fifties, but is just now beginning to emerge as one of the less expensive, more
stable, and temperature-resistant devices.
The late fifties saw the introduction of miniature circuit modules, silicon-controlled
rectifiers (SCR's), and Esaki's remarkable tunnel diode, with which amplification was possible
without the traditional "third element." SCR's shrunk the gap between tube and semiconductor
capabilities by providing a highly efficient solid-state replacement for thryatrons and mercury-arc
rectifier tubes in power control equipment.
What Does The Future Hold?
The pace of development of new transistor types has been absolutely staggering. The list
now numbers in the thousands, and it continues to grow as the mighty midget celebrates its
Apart from its having reshaped an entire industry and opened many new doors, perhaps the
most fascinating offshoot of the whole solid-state technology to date has been the subordinate
art of micro-electronics. Already in the making are integrated circuits so minute that an
entire amplifier could hide behind a single transistor.
Solid-state technology has been growing and changing at such a dizzying pace that it is
difficult to predict what lies ahead even in the next year or so. Perhaps at this very moment,
somewhere in the world, a small but persistent group of experimenters is exploring a radically
new concept that may someday render the present technology obsolete.
*For more details, see article entitled "The 'Coherer'
" which appeared in the May, 1961, issue of Popular Electronics.
Newsreel from 1956, showing William Shockley, Walter Brattain and John
Bardeen receiving the Nobel Prize for the transistor.
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