THEORY OF THE SWEPT INTRINSIC STRUCTURE 



1255 



line at E/Ei = I/aEiA and thereafter remains under it approaching it 

 from below. For positive A the curvature, which is upward near the ori- 

 gin, changes to downward at about x/2Li = -y/A. 



The carrier concentrations n and p can be found from the E versus x 

 curves with the aid of Poisson's equation p — n = 1/a dE/dx and the 

 definition s = (w + p)/2ni with s = I/aE. These relations and (3.4) 

 give 



p — n _ X 

 p + n L 



1 



1 + 



IE,' ' 



(3.7) 



From (3.4) and (3.7) we may distinguish the following two regions 

 on the cubic: 



(1) When E^/Ei is smaller than I/aEi (which as we have seen is 

 usually smaller than unity), the E versus x curve is concave upward, the 

 hole and electron concentrations are almost equal (charge neutrality) 

 and the particle flow is by diffusion. 



(2) When E^/E-^ is greater than I/aEi , in general there is space 

 charge and the particle flow, like the charge flow, is by drift. The curve 

 is concave downward for positive A. 



Figure 6, which we will discuss in Section IV, shows the field and car- 

 rier distributions for L = 2Li and A = 0.665 plotted on a logarithmic 



0.4 0.8 1.2 1.6 2.0 2.4 2 8 3 2 



X/2Ll 



Fig. 4 — Field Distributions for L = GL,- . 



