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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1957 



Table III — The Characteristics of Some High Voltage 

 Rectifiers Processed from Gold Diffused 

 and Zone Refined Silicon 



Silicon-Type 



Gold diffusion 

 p ~ 16,000 fl cm 



Floating zone refined 

 p ~ 6,000 n cm 



1 These units have an area '^ 10^' cm^. 



2 This is the reverse voltage at which these units pass the indicated current. 

 ^ This is the forward bias at which tlie units pass the indicated current. 



^ This is the lifetime measured at 30 milliamperes forward current by the pulse 

 injected technique. The lifetime did not seem very sensitive to small variations 

 in injected current. 



the floating zone apparatus.^^ This technique removes impurities from 

 molten siUcon by treatment Avith hydrogen containing water vapor. The 

 material obtained from this process has an impurity level in the range 

 of 10'' to 5 X 10'' acceptors/cm' (2,000 to 16,000 U cm P type). 



Table III gives the characteristics of some of the better diodes made 

 from such floating zone sihcon . The reverse currents are larger than that pre- 

 dicted by (2.10). The lifetime at high injection is in the order of 1 ^sec. 



N-type silicon with a resistivity range of 10 to 30 fi cm was diffused 

 with gold at 1,200° for sixteen hours. With this diffusion program the 

 gold is uniformly distributed in the material." The resistivity after gold 

 diffusion was in the range of 2,000 to 15,000 fi cm. The characteristics 

 of several devices processed from this material are given in Table III. 

 This technique has many attractive features; however, additional work 

 was not done because the lifetime in the diffused material was consist- 

 ently lower than that reciuired for conductivity modulation. 



One successful purification technique is horizontal zone refining of 

 sihcon in a quartz boat. With the number of passes used, the background 

 acceptor concentration is observed to be in the order of 5 X 10 to 10 

 (100-1,000 fi cm P type). Most of the devices reported in this paper are 

 fabricated from this material. 



Capacity data for devices fabricated from various types of high re- 

 sistivity silicon is shown in Fig. 11. The plot shows that the high resistivi- 



14 



