p-u JUNCTIOXS I.\ SEMI CONDUCTORS 



463 



in germanium. Hence if the transition region is 6 X 10^ cm thick, the 



diffusion capacity Cp will dominate the capacitative term m the admittance. 



Although Ap simulates a conductance and capacitance in parallel at low 



frequencies, its liigh-frequency behav or is quite different. In Fig. 7 the 



10-' 



102 



103 



lOS- 



CcTr 



Fig. 7 — Real, G, and imaginary. 5, components of admittance for hole flow into n-region. 



(a) 10^.1 p /Gpo = 10'(1 + /Wp^''- corresponding to uniform w-region. 



(b) ICF X Formula of Apiicndi.x III, corresponding to layer of high recombination 

 rate in front of n-region. This causes G to exceed 5 at higher frequencies than for (a). 



(c) 10 X Equation (4.33), corresponding to a retarding field in the w-region, with 



U = Lp/VTo. 



(d) Equation (4.33) with Lr = Lp/lO. 



behavior of (1 + io^Tpf'^ = Ap/Gpo , is shown. For high frequencies Gp and 

 Sp are equal: 



Gp = Sp = \/tp/2 Gpo V CO — 



bcTi vo 



(1 + bY<TnV2D 



(4.30) 



Thus for high frequencies the admittance is independent of Tp and is deter- 

 mined by the diffusion of holes in and out of the «-region. The three straight 

 asymptotes have a common intersection at the point G^o , ojt = 2 on Fig. 7, 

 a fact which is useful in estimating the value of r from such data. 



For large w, Sp varies as J'^ as shown in (4.30) whereas ^'riscjCr. Hence 



