Quasi-steady-state photoconductance bulk lifetime measurements on silicon ingots with deeper photogeneration

Abstract

Quasi-steady-state photoconductance measurements on silicon ingots and blocks with different photo-generation profiles are simulated in this work. The results show that deeper generation profiles, achieved by using a long-pass optical filter with a longer cut-off wavelength, can reduce the impact of the high surface recombination velocity of the ingot surface. This results in higher measured effective lifetimes and reduces the reliance on transfer functions to convert the measured lifetimes into bulk lifetimes. However, there exists a trade-off between generating carriers further from the surface to reduce surface recombination and ensuring that the generated carriers are within the sensitivity range of the photoconductance sensing coil. The simulations are compared with experimental results measured on a monocrystalline silicon block using both quasi-steady-state and transient photoconductance decay, as the transient method is relatively less prone to the impact of surface recombination, and provides a lower bound on the bulk lifetime. The results confirm an increased accuracy in bulk lifetimes extracted from quasi-steady-state measurements when measured using deeper photo-generation profiles.