1398 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1956 



be used in designing an appropriate holder. Also, using this equivalent 

 circuit, one may calculate the bandwidth expected for the converter. 



Fig. 13 shows the point contact rectifiers under consideration and an 

 enlarged view of the point contact region. On the right of the figure are 

 shown equivalent circuits of the rectifier. Circuit I is the generally ac- 

 cepted circuit of a point contact rectifier. The true circuit for a rectifier 

 operating at millimeter wavelengths is probably more complicated than 

 that shown in the figure but, for an approximate analysis, the simplified 

 circuit has been found to yield useful results. In the folloAving para- 

 graphs, values are derived for the parameters of this equivalent circuit. 

 MKS units are used and values appropriate to the millimeter wave 

 wafer unit are used as examples. 



Spreading Resistance 



The spreading resistance, Rs , may be calculated if we know the re- 

 sistivity of the silicon used for the rectifier and the radius of the contact 

 area formed when the units are assembled. For DuPont high-purity 

 silicon, doped with 0.02 per cent boron by weight, W. Shockley* gives 

 the resistivity, p, as 0.90 X 10~ ohm meters. From numerous measure- 

 ments on millimeter wave contact areas, R. S. Ohl finds the contact 

 radius, n , to be about 1.25 X 10" meters. The spreading resistance, 



RECTIFIER 

 UNIT 



-SPRING 



ENLARGED 



POINT 

 CONTACT 



EQUIVALENT CIRCUITS 



BARRIER 



SL+0.02%B 

 RESISTIVITY p 



L = INDUCTANCE OF SPRING 

 C= CAPACITANCE OF BARRIER LAYER 

 R = RESISTANCE OF BARRIER LAYER 

 Rs= SPREADING RESISTANCE 



a>C, 



wC 



^(^^) 



R,= 



1 + (a)CR)' 



COL; 





R2=Rs+Ri + 



KM 



Rs + R, 



Fig. 13 — Point contact rectifier and equivalent circuits. 



* W. Shockley, Electrons and Holes in Semiconductors, New York: D. Van 

 Nostrand Co., Inc., 1950, p. 284. 



