DESIGN THEORY OF JUNCTION TRANSISTORS 1305 



of the derivation of these terms follows. The terms are given in the 

 summary. 



For electrons in the emitter: 



at a; = 0, 



Sit X = — 00 



rie = Ueo + Ueie'"' = u^e'"''"' 



in which, again, Ve = Veo + Feie*"' and first-order expansions are used. 

 X = — <x , Tie = Up , is chosen as a boundary condition in order to elimi- 

 nate effects of the emitter contact. Solution of the continuity equation 

 results in: 



noe(t,x) =np+ (noe - n^) e'"- + noie"'"^^""'"' (14) 



in which the r is s = (1 + icxirY'^ now implies electron lifetime in the 

 emitter body. Electron diffusion current at the emitter is computed by 

 means of the equation corresponding to equation (11), giving 



he = ^" ((n.o - Up) + neie'"' (15) 



■Lin 



The ac admittance associated with the last term appears in the sum- 

 mary, Section 1.4. 



The ac electron current from the collector is not a diffusion current, 

 but rather a drift current resulting from the hole current flowing in the 

 collector body. Since the ac electron current is directly proportional to 

 the ac hole current in the collector, the result is an effective multiplica- 

 tion of the output and forward transfer admittances associated with 

 hole current in the collector body.* 



For electrons in the collector the boundary conditions are: 



at 2/ = 0, 



n = n^e''''''^ = (16a) 



at ?/ = 00 , 



n = Up (16b) 



The condition n = at the edge of the barrier region results from Ve 



* Space-charge layer widening effects are neglected since they are usually very 

 small and are difficult to analyze. 



