The Bell System Technical Journal 



Tr)/. XXVIff Jiilw I<^40 \o. 3 



Editorial Note regarding Semiconductors 



ALL but one of the i)apers that comprise this issue discuss practical ap- 

 >- lications of semiconductors and touch upon their properties as em- 

 ployed in rectifying devices, detectors, and in a new amplifying unit — the 

 so-called transistor. These semiconductor papers all relate to one another 

 and present, as a whole, a current but well developed account of the be- 

 havior and uses of these very promising additions to today's vast array of 

 electrical applicances. 



Because semiconductors are relative newcomers, few engineers have as yet 

 had occasion to become familiar with their characteristics and the reasons 

 for their somewhat unexpected performance. Accordingly, it seems appro- 

 priate to preface the present group of papers with a brief introductory note 

 devoted to the nature of the physical phenomena encountered. 



The semiconductors of interest in the communications art are electronic 

 rather than ionic conductors, and include copper oxide, various other oxides, 

 selenium, germanium and silicon. Being electronic conductors, the constitu- 

 ent atoms remain in fixed positions. They may lose or gain electrons during 

 the conduction process but the structure of the conductor as a whole and its 

 chemical composition are not affected. 



Basic to the theory of these semiconductors is the idea that electrons can 

 carry current in two distinguishable and distinctly different ways : one being 

 called "excess conduction," "conduction by excess electrons," or simply 

 "conduction by electrons;" and the other being called "deficit conduction" 

 or "conduction by holes." The possibility that these two processes may be 

 simultaneously and separably active in a semiconductor affords a basis for 

 explaining transistor action. 



We shall confine our attention to the behavior of electrons within the sili- 

 con and germanium type of crystal lattice, and especially as it is modified 

 by minute amounts of suitably chosen ini])urities.' 



' There has been very marked development in the understanding of semiconductors 

 since 1940. This understanding is an outgrowth of the research and development program 

 on crystal rectifiers undertaken in connection with the radar program during the war and 

 continued in several laboratories thereafter. Some of the wartime work was carried out in 

 the Radiation Laboratory of M.I.T., which ojjerated under the supervision of the Xational 

 Defense Research Committee. The Radiation Lal)oratories Series volume "Crystal Recti- 

 fiers" by H. C. Torrey and C. A. Uhilmer reports this program and mentions in particular 

 as chief contrit)utors to cr>-stal research and development in England: the General Electric 



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