Electronic Properties of Light- and Elevated Temperature-Induced Degradation in Float-Zone Silicon

Light- and elevated temperature-induced degradation (LeTID) causes long-term instabilities, especially in passivated emitter and rear cells, leading to severe performance loss of commercial modules. Despite the hundreds of LeTID reports available in the literature, there is little consensus regarding the underlying defects and defect formation mechanism responsible for this degradation and its exact electronic properties. Recently, it has been shown that a form of carrier-induced degradation similar to that of LeTID is also observed in some high-purity silicon crystals grown by the float-zone method. In this work, using deep level transient spectroscopy and lifetime spectroscopy, we study the role of nitrogen on the degradation. Intentional contaminated samples with different and known level of nitrogen have been specially grown and characterized for this study. We detect the appearance of a set of majority carrier traps in the degraded state of the samples with activation energies 0.1 (H85), 0.43 (H270A), 0.39 (H270B), and 0.46 eV (H200) with respect to the valence band, from which H270A appears to correlate with the degradation. The results show that the extent of degradation in the nitrogen-rich samples is at least double that of the nitrogen-lean samples.