DIFFUSED p-n JUNCTION SILICON EECTIFIERS 



CG9 



I 

 O 



< 



UJ 



u 

 z 

 < 



HI 



tr 



100 

 50 



20 



10 



1.0 



0.5 



0.2 



O.t 



0.05 



0.02 



0.01 



0.001 



0.01 0.1 1.0 



CURRENT, Idci'N amperes 



10 



Fig. 5 — Small signal resistance versus dc forward current. 



The departure of the high current data from the exponential charac- 

 teristic is due to the contact resistance. Another interesting measure- 

 ment of the forward characteristic is given in Fig. 5 where the small 

 signal ac resistance is plotted as a function of the forward dc current 

 for a typical rectifier element. The departure from the simple rectifier 

 theory^ where iV = 1 is not surprising inasmuch as p-n junctions made 

 by various methods and of different materials almost always have A^ > 1. 

 Several calculations have been carried out using different assumptions 

 and all indicate that the forward characteristic is independent of the 

 type and resistivity of the middle region as long as the diffusion length 

 for minority carriers is the order of or larger than the thickness of the 

 region. 



3.4 In order to go to higher reverse breakdown voltages (>500 volts) 

 it is necessary to use still higher resistivity starting material. It might 

 be expected that intrinsic silicon will be used for the highest reverse 

 breakdown voltages when it becomes available. How^ever, in this case 



" Shockley, W., B.S.T.J., 28, p. 435, 1949. 



