Useless No More: Gordon K. Teal, Germanium, and Single-Crystal Transistors

In December 1947 Walter Brattain and John Bardeen of Shockley’s group opened up a new era in electronics with their invention of the first working solid-state amplifier using germanium: the point-contact transistor, formed by two closely spaced point contacts atop a piece of a germanium-tin alloy. Shockley, Brattain, and Bardeen won the Nobel Prize for physics in 1956 for this work.

Germanium was certainly no longer useless. It was the material—the alloy of germanium and tin—that allowed the point-contact transistor to exhibit remarkable levels of power and voltage gain. Teal dashed off a number of memoranda to his Bell Labs superiors, now proposing production of single, near-perfect crystals of highly purified germanium. He reasoned that these crystals would give researchers a medium in which the fundamental operation of the transistor could be determined, basic knowledge that would lead to improved devices. Teal’s superiors were aware that imperfections in crystal structure and the presence of chemical impurities were both factors that determined the electrical behavior of semiconductor materials, but they rejected his proposed single-crystal material as needlessly expensive. They felt that if a relatively uniform crystal sample was required, it could be removed from a larger mass of readily available high-purity polycrystalline germanium.

Teal still hoped to initiate a single-crystal program, and his opportunity arrived in fall 1948, when he learned that John Little, a coworker and mechanical engineer, had been assigned to devise a way to cut germanium into uniform slices so as to reduce waste in manufacture. Teal told Little that he could create a rod of germanium with a small, relatively uniform diameter by fashioning it as a single crystal of pure germanium. Teal worked with Little to design and build a new machine, a crystal puller, a device that used seed crystals to draw pure crystals from a molten pool of material. To maintain crystal perfection, Teal and Little had to control a number of variables: the temperature of the melt, the cooling rate of the pulled crystal, and the rate at which the crystal was pulled by the seed crystal. To meet these requirements, their crystal puller employed a melt of ultrapure germanium in a graphite crucible, heated using radio-frequency induction coils. The movement of the seed crystal was governed by an adjustable precision motor. The temperature of the interface between the pulled crystal and the liquid melt was controlled by jets of hydrogen, which also determined the diameter of the pulled crystal. To preserve the chemical consistency of the single crystal, most of the apparatus operated under a bell jar filled with a continually refreshed atmosphere that counterbalanced the inevitable impurities in the original germanium melt.

Impressed by Teal’s success, Jack Morton, head of Bell Labs’ transistor development, allowed him to continue the work in its own right. However, Teal retained his full-time job on the varistor program and had access to his crystal-forming facilities only at night. Pulling germanium single crystals from 4:30 p.m. to 2:00 a.m., he labored through the first half of 1949 to produce the material and spread it around Bell Labs.

In the latter half of 1949 Teal gave batches of his new material to Morgan Sparks, a fellow chemist and a member of Shockley’s group, who in turn gave some of it to a physicist in the group, J. R. “Dick” Haynes. Haynes had earlier collaborated with Shockley on a “crucial experiment” in measuring the electrical properties of germanium samples, work intended to settle definitively what was the basis for transistor action. While Bardeen and Brattain emphasized phenomena at the surface of the germanium as primary to the workings of the transistor, Shockley was convinced that a phenomenon called “minority carrier injection”—involving the bulk of the germanium, not just the surface—was central. Haynes and Shockley’s experiments, which measured “minority carrier lifetimes” in relatively uniform pieces of crystal from a polycrystalline mass of germanium, demonstrated the reality of minority carrier injection and quickly convinced Bardeen and Brattain.

When Sparks gave Haynes samples of Teal’s new single-crystal germanium in 1949, Haynes acted without delay to repeat his crucial experiment using the new material. The result was bracing. Teal’s material showed minority carrier lifetimes 10 times greater than those in the most uniform material harvested from polycrystalline ingots; it thus promised much improved devices and a clearer understanding of transistor action. Shockley was converted to single-crystal material, and the entire research side of Bell Labs quickly followed suit.

Over the next five years Teal’s methods for making single-crystal germanium—and later single-crystal silicon—served as the foundation for an extraordinary flurry of transistor “firsts” at Bell Labs. Teal collaborated with Sparks in using the crystal-pulling method to create the first of a new breed of transistors, the junction transistor, which had been proposed by Shockley. In 1955 another Bell Labs chemist, Morris Tannenbaum, using silicon made by Teal’s method, made the first double-diffused silicon transistor, a device central to the development of the semiconductor industry for a decade.

Teal left Bell Labs in 1952 for Texas Instruments, where he was instrumental in bringing to the market the first silicon transistor based on crystal-growing expertise. In the year of Teal’s departure for his native Texas, Shockley unequivocally connected the successes of Bell Labs in the new electronics to the object of Teal’s passions: “For the last few years, practically all advances at Bell Telephone Laboratories in transistor electronics and transistor physics have been based on the availability of single-crystal material.” Germanium was useless no more.

For Further Reading

Fite, Robert C. “Germanium, a Secondary Metal of Primary Importance.” Scientific Monthly 78 (1954), 15–18.

Goldstein, Andrew. “Finding the Right Material: Gordon Teal as Inventor and Manager.” In Sparks of Genius: Portraits of Electrical Engineering Excellence, ed. Frederick Nebeker (New York: IEEE Press, 1994), pp. 97–99.

Lécuyer, Christophe; David C. Brock. “The Materiality of Microelectronics.” In manuscript.

Riordan, Michael; Lillian Hoddeson. Crystal Fire: The Birth of the Information Age. New York: W.W. Norton, 1997.

Teal, Gordon K. “Single Crystals of Germanium and Silicon—Basic to the Transistor and Integrated Circuit.” IEEE Transactions on Electron Devices ED-23.7 (July 1976), 621–639.