Direct measurement of surface recombination

The direct measurement of surface recombination is not a straightforward task since both theoretical and experimental assumptions must be made. In an early, but extensive discussion, Memming [137] used the following theoretical assumptions to relate surface recombination to directly measurable currents. 

At the surface, the change in carrier concentrations on illumination or other perturbation, Sns and Sps are not equal in fact, we assume 

Inserting the values of natr, pstr, dns and Sps and remembering that 

These equations predict that the effective surface recombination rate, st, decreases as fin0 increases e.g. as the light intensity increases, st should decrease, which corresponds to the Gerischer case (a)- (c) transition, above. 

To verify this relationship, Memming constructed the ingenious cell shown schematically in Fig. 62. If an excess of minority carriers exists at x = W, then a short-circuit current is flows at the p-n junction whose magnitude is given by. 

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