EXCESS SEMICONDUCTOR HOLE TKANSrORT 



AU 



similarly for 7 = 31.6/. Since tiic true curve of v against ^ must lie between 

 the dotted curve and the full curve in each case, it can be concluded that 

 for times and current ratios of this order the difTusionless theory of Section 4 

 gives a useful appro.ximation to the transient when 7 >, 100/. At the other 

 end, it seems likely that for / < 10/ the theory of Section 4 has no quantita- 

 tive utility at all in the transient region. 



When diiTusion effects are sufficiently great, account must also be taken 

 of the fact that the boundary conditions at the injection electrode {x = 0) 



0.09 



0.07 



0.03 



0.02 



0.01 



0.8 



4 = 



Eoy"h7" 



Fig. 10 — Approximate magnitudes of the rounding of the front by diffusion for various 

 values of y/y, for the case < = T,jjja = 2/13, ideal volume recombination. Ordinate is 

 proportional to hole density, abscissa to distance from injection electrode. 



take a different form from those in the absence of diffusion. In the absence 

 of diffusion and with the assumption that only holes are injected at x = 0, 

 the current just to the right of x = must consist of a contribution je from 

 holes and a contribution ja from electrons, while the current just to the left 

 of .V = is purely electronic and of magnitude ja . This implies, as we have 

 seen in Section 2, that the hole density be discontinuous, with the value «/.i 

 given by (12) just to the right of x = 0, and the value zero just to the left. 

 But if diffusion is allowed, the hole density must be continuous. For the 



