Light-induced Recovery of Effective Carrier Lifetime in Boron-doped Czochralski Silicon at Room Temperature

AbstractWe report on the enhancements of effective carrier lifetime by light-induced “recovery” instead of “degradation” in oxygen-rich boron-doped Czochralski-grown silicon (Cz-Si) wafers at room temperature. The highest measured lifetime of τ=550μs was obtained under light illumination at room temperature. We found that the increasing rate of the lifetimes depends on the firing condition and the illumination intensity. These dependencies are very similar to those of permanent recovery caused by hydrogenation of B-O defects or so called regeneration induced by illumination at higher temperatures. Therefore, it can be presumed that the significant increase of minority carrier lifetime is caused by hydrogenation of recombination active defects. However, the defect-inactive state is not stable and the lifetime was found to decrease slowly after the illuminated recovery step. The thermal activation energy of this defect reactivation reaction was obtained to be 0.36eV from the Arrhenius plot, which is much smaller than that of the thermal dissociation of the hydrogenated B-O complex of 1.25eV. This result indicates that the measured defect transitions are markedly different from those of B-O related defects. Possible mechanisms to control defect deactivation are discussed based on a given fractional concentration of charged hydrogen. By combining this deactivation process and a regeneration process, a very high lifetime value could be achieved in Cz-Si for solar cells