SEPARATE DETERMINATION OF THE PHOTOELECTRIC PARAMETERS OF THE BASE REGION OF N+−P(N)−P+ SILICON STRUCTURE BY NONCONTACT METHOD BASED ON QUANTUM EFfi CIENCY RELATION MEASUREMENTS AT TWO WAVELENGTHS

A noncontact method for the determination of recombination parameters of p(n) layer local ranges of silicon n+−p(n)−p+ structures is considered. The method is based on local illumination of the investigated structure by two different absorbed light beams. Initially both beams illuminate simultaneously one side of the local range of this structure and then another side. The intensities оf the light beams are modulated at one frequency so the alternative photo−voltage becomes equal to zero. In this case the short current regime is established for its alternating component. As a consequence the nonilluminated parts of the structure do not shunt its illuminated part. The ratios of the light beam intensities are measured under these conditions. In this work we calculated nomograms for separate determination of the nonequilibrium charge carrier lifetime of the illuminated p(n) local space and its surface recombination velocity using the measured intensity ratios. The calculations were performed at low injection level for one dimensional case. The nomograms were calculated at wave lengths of 1064 and 808 nm for various thicknesses of the n+−p(n)−p+ structures and various modulation frequencies. It was found that the nomograms almost do not depend on the modulation frequency if the live time of the nonequilibrium charge carriers is less than the modulation period. Furthermore, we observed that the nomograms shift substantially and change their shape for thin structures if the diffusion time of nonquilibrium charge carriers from the rear side of the structure to its face side becomes less than their lifetime. In this case the nomograms may be only used for the determination of the surface recombination velocity of the nonquilibrium charge carriers at the rear side of the structure.

silicon, nonequilibrium charge carriers, lifetime, surface recombination rate, solar cells

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