![]() While we could obtain transistor-like effects, the “alpha” of the structures were too low for useful power gain. The results were similar to those of Pearson. By adding a small amounts of N and P type impurities during crystal growth, Buehler produced NPN and PNP structures similar to those that worked so well with germanium. Buehler grew crystals by the Czocralski pulling technique that had been so successful with germanium. We started by repeating Pearson’s work but with silicon produced by Dupont which was significantly purer than that which was available to Pearson. I was joined by Ernie Buehler, a crystal grower par excellance, and Leo Valdes, an electron device engineer, who would characterize any devices that we might make. Initial efforts to make silicon transistorsĪfter a year of III-V study, I was invited by Shockley to lead a small group to study silicon thoroughly and determine if it could be a useful transistor material. However the energy gaps of the new materials I studied were similar to or below that of germanium. It turned out that the crystal and electronic structure of these Group III-IV semiconductors were very similar to those of germanium and silicon. I grew the first single crystals of these Group III-V semiconductors, studied in detail and published the electronic properties of InSb and GaSb. Welker at Siemens in Germany had discovered high values of the electron mobility in the Group III-V compound, polycrystalline indium antimonide (InSb). I had arrived at Bell Labs in 1952 and had initiated a program to search for other semiconducting materials that might have useful properties. In 1953, Bill Shockley decided that it was time to make a more serious attempt to produce useful silicon transistors. Although transistor-like effects were observed in these early structures, they were too weak to construct a device with positive power gain. Later, the presence of that thin oxide layer was found to be very useful in the manufacture and stability of silicon devices, especially integrated circuitry.ĭuring the first few years after the discovery of the transistor effect, efforts were made at Bell Labs by Gerald Pearson to construct a silicon transistor. That made it more difficult to make good electrical contacts. In addition, its chemical reactivity caused it to be coated with a very thin but impervious layer of silicon dioxide whenever it was exposed to the atmosphere. While silicon crystals could be grown by the same techniques as germanium crystals, it was much more difficult to purify. ![]() However, silicon is much more chemically reactive than germanium and also melts at a much higher temperature. Since the temperature dependence of the electrical properties of semiconductors is an exponential function of the energy gap, silicon transistors could operate at significantly higher temperatures and power than germanium. ![]() It was well known that silicon, which is found in the same column of the periodic table (Group IV) and has the same crystal structure as germanium, was also a semiconductor but had an energy gap of 1.1 ev. In addition, the surface of germanium was chemically active and required hermetic enclosures of metal, ceramic or glass for stable operation which significantly increases the cost of germanium devices. ![]() The band gap of germanium (the energy gap between electrons that are bound to the Ge atoms and those that are free to travel throughout the crystal and carry electrical current) was only 0.7 electron volts (ev) and that limited the use of germanium transistors to environments only somewhat above room temperature and, therefore, also to relatively low power applications. Unfortunately, there were two limiting factors in the use of germanium transistors. The discovery ignited a rush to develop practical transistors and incorporate them into electronic circuits. The “transistor effect” was discovered in germanium by Bardeen, Brattain and Shockley in December 1947. 5 Presenting our work and Texas Instruments.3 Initial efforts to make silicon transistors.
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