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THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1956 



CURRENT IN AMPERES 



Fig. 10 — Rectifier characteristics at 25°C. 



It is quite interesting to compare these units with germanium and 

 selenium rectifiers that are commercially available. To make the com- 

 parison as realistic as one can, we have chosen to compare the smallest 

 silicon vuiit with a commercially available germanium unit and a six 

 element selenium rectifier stack rated at 100 milliamperes. The com- 

 parative size of these units can be seen in Fig. 9. Curves of the forward 

 and reverse characteristics at 25°C are given in Fig. 10. Similar curves 

 taken at 80°C are given in Fig. 11 and at 125°C in Fig. 12. It can be 

 seen that the forward characteristic is best for the germanium device 

 at all temperatures and that the reverse currents are least for the silicon 

 rectifier. The selenium rectifier is a poor third in the forward direction. 

 However, if one has to operate the device at 125°C, only the silicon de- 

 vice will be satisfactory in both the forward and reverse directions. 



5.3 Capacitance measurements of all the silicon units have been made 

 at different reverse voltages and temperatures. The temperature depend- 

 ence is negligible. However, as expected in semiconductor rectifiers, 

 the capacitance varies inversely with the voltage according to the rela- 

 tion VC^ = constant where 2 < N < 3. Measurements are given in 

 Fig. 13 for a group of medium size units. The other units made from 

 the same resistivity mat(n'ial have capacitances that vary dii'cctly as 

 their areas. 



