NEGATIVE RESISTANCE IX HEMI('()NDTT(T< )1{ DIODES 



819 



L = x{s) = {JK/f,p/Xe' - /? - 1), 

 jS = as. 

 From these it is found that 



This leads to 



Ingis) = (1 - e-^. 



D(t) = (J/tJLpi) [/ + e"' (at - 

 = (J//XP/) Di^, at). 



- 1)] 



(4.27) 



(4.29) 



(4.30) 



For t = this reduces correctly to L/K. 



Figure 4.4 shows the resulting shape of the D curves with /3 as a 

 parameter. Large values of (3 correspond to cases in which the hole 

 charge density is small compared to p/ and to relatively long relaxation 

 constants. For them the desired convex upward shape results. 



Figure 4.5(a) and 4.5(b) show the real and imaginary parts of the 

 impedance expressed in terms of Z{^, 6) : 



Jo 



'D(t) dt 



= {KJ/^.Vf)Z{^, d), 



= coT. 



(4.31) 



(4.32) 



0.8 

 Q 0.6 



s 



Q 0.4 



0.2 4 6 0.8 10 



at//3 

 Fig. 4.4 — Impulsive impedance lor various values of /3 in p-n-p structure. 



