MAPPING OF THE LOCAL MINORITY-CARRIER DIFFUSION LENGTH IN SILICON-WAFERS

A new instrument based on the light beam induced current (LBIC) technique for the determination of the local minority carrier diffusion length L in silicon samples is presented. The evaluation of L is done by measuring the spectral variation of the normalized photocurrent as collected by a diode structure under local excitation by a light spot for wavelength lambda in the near infrared range. Mappings of L(x,y) are obtained by scanning the sample under the spot in x-y direction. White light bias applied during the measurement gives informations about saturation effects at recombination centers. Applications of this technique are given for multicrystalline wafers treated by phosphorus diffusion for a differing time, and for silicon bicrystals prior and after heat treatments. The evolution of L(x,y) in the grains and at extended defects is discussed in relation to the sample processing.