After William Shockley’s theories about p-n junctions had been validated by tests (1948 Milestone), fabricating a working junction transistor still presented formidable challenges. The main problem was lack of sufficiently pure, uniform semiconductor materials. Bell Labs chemist Gordon Teal argued that large, single crystals of germanium and silicon would be required, but few - including Shockley - were listening.
With little support from management, Teal built the needed crystal-growing equipment himself, with help from mechanical engineer John Little and technician Ernest Buehler. Based on techniques developed in 1917 by the Polish chemist Jan Czochralski, he suspended a small "seed" crystal of germanium in a crucible of molten germanium and slowly withdrew it, forming a long, narrow, single crystal. Shockley later called this achievement "the most important scientific development in the semiconductor field in the early days."
Employing this technique, Bell Labs chemist Morgan Sparks fabricated p-n junctions by dropping tiny pellets of impurities into the molten germanium during the crystal-growing process. In April 1950, he and Teal began adding two successive pellets into the melt, the first with a p-type impurity and the second n-type, forming n-p-n structures with a thin inner, or base, layer. A year later, such “grown-junction transistors” surpassed the best point-contact transistors in performance. Bell Labs announced this advance on July 4, 1951 in a press conference featuring Shockley.
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