The grown-junction transistor was the first type of bipolar junction transistor made. It was invented by William Shockley at Bell Labs on June 23, 1948 (patent filed June 26, 1948), six months after the first bipolar point-contact transistor. The first germanium prototypes were made in 1949. Bell Labs announced Shockley’s grown-junction transistor on July 4, 1951.
An NPN grown-junction transistor is made of a single crystal of semiconductor material which has two PN junctions grown into it. During the growth process, a seed crystal is slowly pulled from a bath of molten semiconductor, which then grows into a rod-shaped crystal (boule). The molten semiconductor is doped N-type at the start. At a predetermined moment in the growth process a small pellet of a P-type dopant is added, almost immediately followed by a somewhat larger pellet of an N-type dopant. These dopants dissolve in the molten semiconductor changing the type of semiconductor subsequently grown. The resulting crystal has a thin layer of P-type material sandwiched between sections of N-type material. This P-type layer may be as little as a thousandth of an inch thick. The crystal is sliced, leaving the thin P-type layer in the center of the slice, then cut into bars. Each bar is made into a transistor by soldering its N-type ends to supporting and conducting leads, then welding a very fine gold lead to the central P-type layer, and finally encasing in a hermetically sealed can. A similar process, using the opposite dopants, makes a PNP grown-junction transistor.