240 BELL SYSTEM TECHNICAL JOURNAL 



in the Letters to the Editor columns of the Physical Review.^ Accom- 

 panying this letter were two further communications on related subjects.-' ' 

 Since these initial publications a number of talks describing the characteris- 

 tics of the device and the theory of its operation have been given by the 

 authors and by other members of the Bell Telephone Laboratories stafif.^ 

 Several articles have appeared in the technical literature.^ 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. G. Pfann, is shown in Fig. 2. 

 The transistor can be used for many functions now performed by vacuum 

 tubes. 



During the war, a large amount of research on the properties of germa- 

 nium and silicon was carried out by a number of university, government, 

 and industrial laboratories in connection with the development of point 

 contact rectifiers for radar. This work is summarized in the book of Torrey 

 and Whitmer.'' The properties of germanium as a semi-conductor and as 

 a rectifier have been investigated by a group working under the direction of 

 K. Lark-Horovitz at Purdue University. Work at the Bell Telephone 

 Laboratories^ was initiated by R. S. Ohl before the war in connection with 

 the development of silicon rectifiers for use as detectors at microwave 

 frequencies. Research and development on both germanium and silicon 

 rectifiers during and since the war has been done in large part by a group 

 under J. H. Scaff. The background of information obtained in these 

 various investigations has been invaluable. 



The general research program leading to the transistor was initiated and 

 directed by W. Shockley. Work on germanium and silicon was emphasized 

 because they are simpler to understand than most other semi-conductors. 

 One of the investigations undertaken was the study of the modulation of 

 conductance of a thin film of semi-conductor by an electric field applied by 

 an electrode insulated from the film.^ If, for example, the film is made one 

 plate of a parallel plate condenser, a charge is induced on the surface. If 

 the individual charges which make up the induced charge are mobile, the 

 conductance of the film will depend on the voltage applied to the condenser. 



