p-n JUNCTIONS IN SEMICONDUCTORS 



437 



Even for distributions of impurities as simple as those shown in part (b) 

 there are two distinctly diflferent types of behavior of the electrostatic po- 

 tential in the transition region, each of which may be either rectifying or 

 nonrectifying. The requirement that the junction be rectifying can be stated 

 in terms of the current distribution, certain cases of which are shown in (c). 

 The total current, from left to right, is /, the hole and electron currents being 



Xb 



DISTANCE THROUGH SAMPLE, X *- 



Fig. 1 — The p-n junction. 



(a) Schematic view of specimen, showing non-rectifying end contacts and convention 

 for polarities of current and voltage. 



(b) Distribution of donors and acceptors. 



(c) Three possible current distributions. 



Ip and /„ , with I = Ip-\- In- Well away from the junction in the p-type 

 material, substantially all of the current is carried by holes and Ip = I; 

 similarly, deep in the «-type material In = I and I p = 0. In general in a 

 nonrectifying junction, the hole current does not penetrate the ;z-type ma- 

 terial appreciably whereas in the rectifying junction it does. Under some 

 conditions the major flow across the junction will consist of holes; such 



