CONDUCTIVITY-MODULATED SILICON' RECTIFIER 



985 



1012 



lO'S 2 5 ,Q,4 2 5 ,Q,5 2 5 ,q,6 



Nj IN ATOMS PER CUBIC CENTIMETER 



10'7 



Fig. 5 — Breakdown voltage versus impurity concentration for silicon step 

 junctions. 



S.2 Experiment 



Fig. 5 is a plot of breakdo\\'ii voltage versus impurity concentration 

 for silicon step junctions. The plot above 300 volts is extrapolated from 

 the data of Miller^" and Wilson.' 



Capacity data, discussed in Section V, indicates that many devices 

 show body breakdown. A few rectifiers break down at voltages as high 

 as 2,000 volts. In many high voltage devices the breakdo^^^l voltage is not 

 limited by geometry but by surface problems. 



IV FORWARD CURRENT-VOLTAGE CHARACTERISTIC 



4-1 Theory 



It will be shown in this section that the forward current- volt age char- 

 acteristic as well as the reverse characteristic can be completel\' explained 

 by considering both a space-charge region generated current and a diffu- 

 sion current. The diffusion current component must also take into con- 

 sideration the effect of high injection levels of minority carriers. 



According to the Shockley-Read- theoiy, the rate of recombination, 

 U, of holes and electrons in a semiconductor is given by: 



U = -G = 



pn 



71 i 



Tpo{n + rii) 4- Tno(p + Pi) 



(4-1) 



