Sec. 5-1] 



RA DIA TION TRA XSD UCERS 



273 







/00 



200 

 300 

 400 



700 



1,000 



1,500 



2,000 



10 20 



Temperature, °C 



30 



40 



Fig. (5-1)35. Temperature effect on a photogalvanic cell. Ordinate, 

 variation of current output in percentage of the output at 20°C; 

 parameter load resistance {Weston Instruments, Division of Day- 

 strom, Inc.; by permission). 



(r^y 



-P-N junction 



-Plostic 



Light 



Germanium wafer 

 0.003" thick 



Fir;. (5-1)36. Germanium 

 photodiode, cross section 

 [from J . X . Shive, Bell Labs. 

 Record, 28, 337 (1050); by 

 permission]. 



Plastic block 



Fig. (5-1)37. PN junction 



photodiode [from J. N. 

 Shive, Proc. IRE, 40, 1 4 1 1 1. 



(1952); by permission]. 



from that of a photogalvanic cell to that of a photodiode. Photo- 

 diodes have in general a much smaller area; therefore, their capaci- 

 tance is smaller and their frequency response is higher. The con- 

 struction of two types of germanium photodiodes is shown schemati- 

 cally in Figs. (5-1)36 and (5-1)37. The sensitive area is usually of 



