Separate determination of the photoelectric parameters of n+-p(n)-p+ silicon structure base region by noncontact method based on measurements of quantum efficiency relationships at two wavelengths

A noncontact method for determination of recombination parameters of p(n) layer local regions in n+–p(n)–p+ silicon structures is considered. The method is based on local illumination of the investigated structure with two differently absorbed light beams. The two beams simultaneously illuminate initially one side of a local range of the structure and then the other side. The intensities оf the light beams are modulated at one frequency so the alternating photovoltage becomes zero. In this case short circuit current mode 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 carrier lifetime for the illuminated p(n) local region and the carrier surface recombination rate using the measured intensity ratios. The calculations were performed at low injection for one dimensional case. The nomograms were calculated at 1064 and 808 nm wavelengths for various thicknesses of the n+–p(n)–p+ structures and various modulation frequencies. We found that the nomograms depend little if any on the modulation frequency if the nonequilibrium carrier lifetime is less than the modulation period. We also established that the nomograms of thin structures undergo essential shifts and changes in pattern if the diffusion time of the nonquilibrium carriers from the rear side of the structure to its face side becomes shorter than the nonequilibrium carrier lifetime. In this case the nomograms can only be used for determining the surface recombination rate of the nonquilibrium carriers at the rear side of the structure