Beginning in 1952 Bell Labs chemist Calvin Fuller demonstrated how impurities could be introduced into germanium and then silicon by exposing them to high-temperature gases containing desired dopants. By adjusting the time and temperature of exposure, he could precisely control the amount of impurities introduced and their penetration depth to accuracies of better than one micrometer — far better than achievable with grown-junction techniques.
Working with engineer Daryl Chapin and physicist Gerald Pearson in early 1954, Fuller diffused a layer of boron atoms into wafers of n-type silicon, forming large-area p-n junctions just beneath the surface. By shining light on these junctions, they generated a strong electric current via the photovoltaic effect discovered by Ohl in 1940, (1940 Milestone) getting energy conversion efficiencies up to 6 percent. Bell Labs announced this solar cell, dubbed the "Solar Battery," on 26 April 1954. By the late 1950s, solar cells were powering rural telephone systems and space satellites.
Later that year Charles Lee used diffusion to make transistors with base layers only a micrometer thick; they could operate at frequencies up to 170 MHz - ten times higher than earlier devices. And in March 1955, employing silicon wafers into which Fuller had diffused two different impurities to form a three-layer n-p-n sandwich, chemist Morris Tanenbaum and his technician D. E. Thomas fabricated silicon diffused-base transistors. In January 1956 Bell Labs held a third symposium on transistor technology (1952 Milestone) specifically devoted to these and other diffusion techniques.
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Chapin, D. M., Fuller, C. S. and Pearson, G. L. "A New Silicon p-n Junction Photocell for Converting Solar Radiation into Electrical Power," Journal of Applied Physics Vol. 25 (May 1954) pp. 676–77.
Tanenbaum, M. and Thomas, D. E. "Diffused Emitter and Base Silicon Transistors." Bell System Technical Journal, Vol. 35 (January 1956) pp. 1–22.
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Hornbeck, J. "The Transistor," in F. M. Smits, ed., A History of Science and Engineering in the Bell System: Electronics Technology (1925–75) (AT&T Bell Laboratories, 1985) pp. 1–100.
Lojek, B. "History of semiconductors diffusion engineering," 10th IEEE International Conference of Advanced Thermal Processing of Semiconductors (September 25-27, 2002) pp. 209-241