DC FIELD IN A "sWEPT INTRINSIC" SEMICONDUCTOR 689 



The minority carrier concentration at the interfaces depends too, on 

 the neighboring extrinsic material, but is also U dependent: 



^ « e-'e-^", (57) 



^ « e-'e-'". (58) 



At the point of minimum field intensity, ^ = and 



J = |«e-e- (59) 



The extremely low carrier concentrations given by (57)-(59) are not 

 really meaningful, of course, because the analysis has neglected the 

 carrier concentrations due to thermally generated hole-electron pairs 

 and to saturation currents injected through the biased junctions. While 

 these latter concentrations are neghgible compared to (55) and (56), 

 they are undoubtedly large compared to (57) and (58). Therefore, al- 

 though they can be neglected in determining the electric field intensity 

 distribution, they are of principal importance in determining the small 

 residue carrier concentrations in the "swept" region. A computation of 

 these concentrations can be made by regarding the fields determined 

 in the present analysis as impressed and studying the resulting motion 

 of the generated and injected carriers. 



Appendix I 



EVALUATION OF INTEGRATION CONSTANTS A, B, AND C. 



In this section the conditions described in (7)-(12) will be used to 

 evaluate the integration constants J., B, and C in terms of the pre- 

 scribed parameters L, U, and A. 



First a partial integration of the differential equations for the extrinsic 

 regions will be performed to obtain from (7)-(10) relations between 

 JS and n at ^ = and J§ and p aty = L. Division of (25a) by (27) gives 

 (for the n-region ^ < 0) 



dn ' n 



= 1-?-^. (00) 



Addition of n times (26) to p times (27) yields 



^ ipn) = 0, 

 dy 



