472 BELL SYSTEM TECIIMCAL JOLRSAL 



absence of thermal equilibrium, different i)otentials depending on the niiture 

 of the contact are, in general, the rule rather than the exception. 



'Ilie bias developed on /\> or c will change its conductance. If we suppose 

 that (^c and ipi, are held constant, then the current flowing into c is obtained 

 by the same reasoning that led to (5.7) and is 



/e((^,., ip,) = InfM + coth ^ Ip(Uc) - csch j^ Ip„M. (5.13) 



For an infniitesimal change in s^, from the value which makes Ic{(Pc , ft) 

 vanish, the admittance to c is readily found from (4.18) and (4.19) to be 



l~) = l'ni){<Pc) + coth "-^ I'p^i^c) 



(^.14) 

 G^o + coth^GpoJg""^'" 



which shows that pronounced variations in admittance should be associated 

 with variations in hole density in X in Fig. 10. "^ 



6. p-n-p Transistors 



The structure shown in Fig. 10 is a transistor w'ith power gain provided 

 the distance w is not too great. As a first approximation, we shall neglect 

 the drop due to currents in the .A' region. If we use Po as the collector and call 

 the collector current, /, , positive when it Rows into Po from outside, we shall 

 have from (5.13) 



Ic - —csch -=— Ipoitpe) + coth ^ Iptt{(pc) + I„q{<Pc)- (6.1) 



The emitter current is similarly 



'2.7U ^11) 



If = coth y- Ipoi^t) — csch — Ipi\((Pc) + Ino(^e)- (6.2) 



■L'P -Lip 



If pn » II,, , then the /„n terms can be neglected. However, the base current 

 will not vanish but will be 



r lie 



csch — 

 L. J-p 



2 sinh" w/Lp 



/fc = —Ii — Ic — \ csch — — coth — 



sinh 2w/Lf 



Upo(v?t) + Ipc(<p,)] 



(6.3) 



[/;,n(v^) + Ip,M]. 



'^ The variations in adiniltance discussed in connection with metal point contacts in 

 an accompanying j^ajicr in this issue (W. Shoclcley, G. L. Pearson and J. R. Haynes, Bell 

 Sys. Tech. JL, July, 1949), arise from this cause; however, the nature of the contact is 

 not as simple as here. 



