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BELL SYSTEM TECHNICAL JOURNAL 



that by changes in processing routines the direct-current characteristics 

 shown in Fig. 10 may be modified in a predictable manner, particularly 

 with respect to absolute values of forward current at a particular voltage. 



Modern Rectifier Processes 



When the development of the type 1N21 unit was undertaken, the scien- 

 tific and engineering information at hand was insufficient to permit inten- 

 tional alteration or improvement in electrical properties of the rectifier. 

 In these early units, the control of the radio frequency impedance, power 

 handling ability and signal-to-noise ratio left much to be desired. Within 

 a short time, some improvements in performance were realized by process 

 improvements such as the elimination of burrs and irregularities from the 

 point contact to reduce noise. Substantial improvements were not obtained, 



I0-' 



however, until certain improved materials, processes, and techniques were 

 developed. 



In the engineering development of improved cr>'stal rectifier materials 

 and jjrocesses, basic data have been acquired which make it possible to 

 alter the properties of the rectifier in a predictable manner so that tlie units 

 may now be engineered to the specific electrical requirements desired by 

 the circuit designer in much the same manner as are modern electron tubes. 

 This has led not only to improvements in performance but also to a diver- 

 sification in types and applications. 



The simplified equivalent circuit for the point contact rectifier, shown 

 in Fig. 11, provides a basis for consideration of the various process features. 

 In Fig. 11, Cb represents the electrical capacitance at the boundary between 

 the point contact and the semi-conductor, Rn the non-linear resistance at 

 this boundary, and /^s is the spreading resistance of the semi-conductor 



