Modulating the field-effect passivation at the SiO2/c-Si interface: Analysis and verification of the photoluminescence imaging under applied bias method

Abstract

In this paper, we study the surface passivation properties of thermally oxidized silicon wafers with controlled surface band bending, using a recently developed characterization technique combining calibrated photoluminescence imaging with the application of an external voltage over the rear side passivation layer. Various aspects of the technique and possible errors in the determination of the effective surface recombination velocity are discussed, including lateral carrier diffusion, leakage currents, and optical effects related to the presence of metal electrodes on the investigated samples. In order to quantitatively describe the recombination activity at the SiO2/c-Si interface and the effect of fixed charges in the oxide layer, the measured effective carrier lifetime vs. voltage curves have been analyzed in the framework of an extended Shockley-Read Hall recombination model. Furthermore, the results have been compared with corresponding results from microwave detected photoconductance decay measurements after depositing corona charges. We find an excellent agreement between the two techniques and between complementary measurements of the oxide charge density. Photoluminescence imaging under applied bias gives fast and repeatable measurements and allows for simultaneous data collection from multiple areas on the sample, and has thus been proven to be powerful tool for quantitative characterization of surface passivation layers.