Comment on “Direct measurement of minority carriers diffusion length using Kelvin probe force microscopy” †Appl. Phys. Lett. 75, 2435 „1999…‡

摘要

A scanning Kelvin probe microscopy based method forndetermining minority carrier diffusion length was presentednin Ref. 1. The authors claim that diffusion length measurednby this method is independent of surface recombinationnvelocity.n1nWe point out that this claim is applicable only inncase of low surface recombination velocity and the effect ofnsurface recombination has to be taken into account in apply-ning this method to high surface recombination velocity cases.nIf surface recombination velocity is low, minority carrier dif-nfusion toward the surface is negligible compared to diffusionntoward the p–n junction in the Fig. 1 of Ref. 1 such thatndiffusion toward the surface has negligible effect on minorityncarrier density at the edge of surface space charge region andnthe surface potential profile shown in the Fig. 3 of Ref. 1 isna reliable representation of minority carrier density gradientnresulting from diffusion toward the p–n junction in the bulk.nminority carrier diffusion toward the surface can be compa-nrable to diffusion toward the p–n junction. Therefore minor-nity carrier distribution near the meeting point of a p–n junc-ntion and a high recombination velocity surface is governednby a two-dimensional diffusion equation. Numerical simula-ntions of two-dimensional diffusion equations near a p–nnjunction under illumination have shown significant role ofnsurface recombination on minority carrier distribution whichndeviates considerably from the distribution obtained from thensolution of a one-dimensional diffusion equation.n2nHence fornhigh surface recombination velocity cases the minority car-nrier distribution given by the Eq. u00024u0003 in Ref. 1 should benreplaced by the solution of a two-dimensional diffusionnequation subject to an independently determined surface re-ncombination velocity as one of the boundary conditions.