Calibration factors for lifetime measurements on Si ingots with a localized PCD method [solar cell fabrication]

The relationship between measured effective lifetime /spl tau//sub e/ and bulk lifetime /spl tau//sub b/ of minority carriers in silicon ingots by a localized photoconductance decay method has been determined with a full 3-dimensional and transient finite-element analysis. For an excitation light with a spot size of 3 mm /spl times/1 mm and an absorption coefficient of 100 cm/sup -1/, the ratio of /spl tau//sub e/ to /spl tau//sub b/ ranges from 0.95 at /spl tau//sub b/=1 /spl mu/s and a surface recombination velocity S=10/sup 2/ cm/s to 0.573 at /spl tau//sub b/=100 /spl mu/s and S=10/sup 8/ cm/s. This effect originates from both surface recombination and carrier diffusion from a localized light excitation.