Physical Principles Involved in Transistor Action

HE transistor, a semi-conductor triode which in its present form uses a small block of germanium as the basic element, has been described briefly * This paper appears also in the Physical Review, April 15, 1949. 239 240 BELL SYSTEM TECHNICAL ' . J O U R N A L in the Letters to the Editor columns of the Physical Review.1 Accompanying this letter were two further communications on related subjects. 2 - 3 Since these initial publications a number of talks describing the characteristics of the device and the theory of its operation have been given by the authors and by other members of the Bell Telephone Laboratories staff.4 Several articles have appeared in the technical literature. 6 We plan to give here an outline of the history of the development, to give some further data on the characteristics and to discuss the physical principles involved. Included is a review of the nature of electrical conduction in germanium and of the theory of the germanium point-contact rectifier. A schematic diagram of one form of transistor is shown in Fig. 1. Two point contacts, similar to those used in point-contact rectifiers, are placed in close proximity (-- .005-.025 cm) on the upper surface of a small block of germanium. One of these, biased in the forward direction, is called the emitter. The second, biased in the reverse direction, is called the collector. A large area low resistance contact on the lower surface, called the base electrode, is the third element of the triode. A physical embodiment of the device, as designed in large part by W.