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

Gordon Teal (left) and fellow chemist Morgan Sparks. Property of AT&T Archives. Reprinted with permission.

By David C. Brock

By 1952 it seemed certain that the advantages of the transistor—reduced size, enhanced performance, and increased reliability—spelled the demise of the vacuum tube as the central component in the electronics world. These virtues of the transistor were due to the unique use of materials in its formation. As William Shockley noted in that year’s Proceedings of the IRE: “Transistor electronics exists because of the controlled presence of imperfections in otherwise nearly perfect crystals.” An accomplished physicist at Bell Telephone Laboratories, Shockley had recently invented an important new breed of transistor that fundamentally relied on single crystals of germanium. The key actor in the development of these crystals was Gordon K. Teal, a chemist captivated by germanium and determined to conquer its “uselessness.”

Germanium is a semiconductor, with the same crystal structure as diamond and electrical properties somewhere between those of conductive metals and nonconductive insulators. It was discovered in 1886 by Clemens Winkler, who named the grayish-white, lustrous substance after his homeland, but Dmitri Mendeleev had predicted its existence between silicon and tin in the periodic table more than a dozen years earlier.

Teal fell under the spell of germanium while earning his Ph.D. in chemistry at Brown University during the 1920s. As he put it in 1976, germanium “was [then] a material studied only for its scientific interest; its complete uselessness fascinated and challenged me. My concentration on this shiny metallic-appearing material during my graduate school days resulted in a continuing personal sentimental attachment for germanium, which, to me, at least, was and is an exotic element.”

In 1930 Teal left his university studies to join Bell Labs, which in the 15 years preceding World War II was at the forefront of R&D in vacuum-tube electronics. After a brief stint in the chemical research department, Teal was redeployed to the electro-optical department, which was working hard on new television systems. Teal’s mandate was to form a variety of materials into novel structures for use in electronic television components.

Teal was not the only chemist in Bell Labs’ extended organization whose research focused on materials in advanced electronic systems. Around 1935 Russell Ohl and several coworkers at a branch facility in Holmdel, New Jersey, were involved in projects on radio systems utilizing wavelengths much shorter than those of mainstream systems. They encountered a stumbling block: vacuum tubes used for conventional radio did not perform well with the new wavelengths. Ohl’s solution was to resurrect an antiquated radio technology—the crystal rectifier, the temperamental receiving element used in early radio sets. Investigating a range of crystalline materials, Ohl unsurprisingly turned his attentions to the chemical element silicon, a common ingredient in many of the old crystal “point-contact” rectifiers—devices that rely on the contact between a metal wire and a crystal to convert alternating into direct current, thus allowing them to receive radio transmissions.

Silicon is similar in appearance to germanium, but whereas Teal found germanium “exotic,” silicon is arguably prosaic. It is the second most abundant element on earth, contributing over a quarter of the weight of the planet’s crust; oxygen, the most abundant, contributes just under half. Silicon rarely reveals itself in its elemental form, instead appearing in mixtures, of which quartz and silica (sand) are familiar examples.

At the end of the 1930s Ohl, convinced that using chemically pure silicon crystals in point-contact devices would cure the erratic performance of earlier rectifiers, was working on purifying silicon material—melting and cooling it to isolate impurities. In early 1940 he observed a new and puzzling behavior in one of his polycrystalline silicon samples: the electrical conductivity of the silicon piece changed when he shone light on it. The silicon sample was itself acting as a rectifier, and a photosensitive one at that. Ohl and his colleagues determined that this rectifying action was caused by the junction of two chemically distinct regions within the polycrystalline silicon sliver. On one side of the junction lay silicon with traces of boron, which was deficient in available electrons; it was soon dubbed “P-type” (for positive) silicon.

On the other side lay silicon with traces of phosphorus, or “N-type” (negative) silicon, which had a surfeit of electrons. Ohl had discovered the P-N junction. The Bell Labs leadership was enthralled. Ohl’s P-N junction opened up the possibility for new photosensitive devices and rectifying diodes in which the material was the device.

Ohl’s work had implications for Teal’s work on photosensitive materials for television and undoubtedly resonated with Teal’s attachment to silicon’s cousin on the periodic table, germanium. Teal now saw that germanium’s uselessness might be an illusion—if silicon could form a rectifier, so might germanium. He hurriedly created some films of purified germanium material (deposited pyrolytically from germanium hydride gas) and personally brought them to Ohl’s Holmdel crew. However, the branch laboratory continued to focus on silicon rather than Teal’s import.

When Bell Labs shifted its priorities to accommodate important new war-related R&D like radar, its commitment to television research was drastically reduced. Teal returned to the chemical research department. In early 1942 he began to improve his method for making polycrystalline germanium, yielding P- or N-type material to use in pointcontact rectifiers. But he soon went further and created a germanium rectifier itself. His system—a complex jungle of glass tubes, gas lines, flow meters, valves, heaters, and reaction vessels—relied on controlled mixing in a reaction chamber of germanium chloride gas and a chloride gas mixed, or “doped,” with the desired impurity (e.g., boron). The mixed gases decomposed as they passed over heated elements and deposited layers of a germanium-impurity alloy on a metal base at the bottom of the chamber. The surface of the alloy was then etched and a metal-wire point contact was applied, yielding the final germanium rectifier.

Teal’s system hardly made a splash at Bell Labs, which had set its course firmly on silicon rectifiers. Disappointed, he switched his focus, adapting his germanium approach to incorporate silicon. Soon he was producing silicon-germanium resistors, depositing film on ceramic substrates. These had highly desirable resistance and temperature characteristics, but Teal’s research still failed to make waves at Bell Labs.

Ironically, while Teal was out of work for an extended stretch (probably with chemical pneumonia linked to his inhalation of noxious substances in a laboratory mishap), the MIT Radiation Laboratory prevailed on Bell Labs to undertake a crash program for germanium rectifiers, and Bell gave that work to others. On his return, Teal was assigned to other, non-germanium research for radar components.

Immediately after the war, however, he returned to work on semiconductors, managing the materials aspect of a large-scale project that used a silicon compound to create a new electronic component known as a varistor, a variable resistance element for use as a static and crackle buster in telephone handsets. Elsewhere in Bell Labs a semiconductor research group was formed under William Shockley, whose mandate was to conduct fundamental studies on the electronic behavior of silicon and germanium—with an eye to possible new devices based on that behavior.