Investigation of Carrier Recombination at the SiO $_{2}$ /c-Si Interface by Photoluminescence Imaging Under Applied Bias

A new technique to analyze the surface recombination for passivated silicon substrates has been employed to study the SiO₂/c-Si interface under various band bending conditions. A photoluminescence imaging setup was used to measure the effective minority carrier lifetime of oxidized Si wafers while applying an external bias over the rear side passivation layer. This method was used to investigate both the effect of substrate doping polarity and postoxidation forming gas anneal (FGA) upon the surface passivation properties. The measured carrier lifetimes as a function of voltage were interpreted in the framework of the extended Shockley-Read-Hall theory. The calculated oxide charge density was found to decrease from ~7 × 10¹¹ cm ^-2 to ~4 × 10¹¹ cm^-2 after the FGA treatment for both p-type and n-type substrates, causing a reduction in the field effect passivation. On the contrary, an increased chemical passivation was observed after FGA, shown by a reduction of the effective surface recombination velocity parameters by a factor of 3.8-5.5. In total, a significant increase in the effective carrier lifetime was obtained for both substrate types. Furthermore, the carrier capture efficiency at the surface defects was found to be 2-2.5 times higher for electrons than for holes, regardless of doping polarity and FGA.