Determination of the grain boundary recombination velocity in polycrystalline silicon as a function of illumination from photoconductance measurements

The grain boundary recombination velocity of polycrystalline Si is separated from bulk effects and its value is determined with practically no assumption of numerical values for any parameter other than the minority carrier diffusion coefficient. The method used utilizes photoconductance measurements taken by the scanning laser spot technique. It is found that, for the illumination levels used, there is a transition from low level to high-level injection of minority carriers, and this transition is used to estimate the quasi-Fermi level separation. The recombination velocity S, ranging in value from 5000 to 17000 cm/sec, is thus presented both as a function of the illumination level as well as of the quasi-Fermi level separation ΔE_f. It is found that S increases monotonically with illumination and does not saturate, even at the high light concentrations used.