p-n JU.\CTIO.\.S l.\ .SKMlLUM)rcmRS 



465 



//) 'flic Effect oj a Rcgitvi of Iliiih Rule of Gntcralioii 



Thore is cvideiux tl\at iniporlCclions, such as surfaces and cracks, add 

 materially to ihe rale of ^a'neration and recombination of holes and elec- 

 trons. If there is a localized region of high recombination rate in the transi- 

 tion region, there will be a pronounced modification of the admittance char- 

 acteristics. In Fig. 8(a) such a layer is represented at .v = 0. In Fig. 8(b) 

 the customary plot of ^p and v?,, versus .v is shown. If we neglect the efTect 

 of the series resistance terms denoted by Rx in Section 3, the change h<p will 



TRANSITION 

 REGION 



DISTANCE THROUGH SAMPLE, X 



Fig. 8 — The eiYect of a localized layer of high recombination rale on the junction 



characteristic. 



(a) Location of layer of high recombination rate. 



(b) Quasi Fermi levels. 



(c) Distribution of hole current showing rapid change at layer of high recombination 

 rate. 



occur in the /^-region for ^„ and in tlie //-region for <p ,, . The hole current flow- 

 ing into the //-region will thus be the same as before and will be given by 

 equation (4.11) or (4.18) and denoted by l^uM. Similarly, the electron 

 current will be /„o(M- I'l the layer we shall suppose that there is a rate of 

 generation of hole electron pairs equal to ga per unit area of the layer and a 

 rate of recombination proportional to /-„;//> per unit area. We sui)pose, further- 

 more, that the layer is so thin that // and p are uniform throughout the layer. 

 The net rate of generation is thus 



.?'< 



r.np = ^Jl - e"^'"-^'"'"'''] 



(4.34) 



