Impact of Gettering and Hydrogenation on Sub-Band-Gap Luminescence from Ring Defects in Czochralski-Grown Silicon

Ring defects often occur in n-type Czochralski-grown silicon wafers during intermediate- to high-temperature annealing and become more recombination-active with increasing anneal durations. Such defects can significantly reduce the efficiency of solar cells. In this work, low-temperature photo-luminescence (PL) spectra were measured from such ring defects, which emit a broad defect-related luminescence (DRL) peak centered at 0.9 eV. Quantitative comparisons of the DRL peak area between samples are generally not possible when using a constant laser power due to the significantly different carrier lifetimes, resulting in a different injection level and peak intensity. We show that this complication may be circumvented by varying the excitation laser power to achieve a constant band-band PL intensity from each sample, resulting in the same average injection level. The broad DRL peaks were then deconvoluted into three individual component peaks centered at 0.88, 0.93, and 1 eV. The impact of hydrogenation and phosphorus diffusion gettering steps was investigated on the individual components of the DRL peaks. Both hydrogenation and phosphorus diffusion gettering steps suppressed the broad DRL peak. However, the individual deconvoluted peaks were suppressed to different degrees. We observed that when the component peak from the deeper energy level (0.88 eV) is dominant, the ring defects can be completely passivated by hydrogenation. However, when the component peaks from the shallower energy levels (0.93 and 1 eV) dominate the DRL peak, hydrogenation is less effective for the passivation of ring defects.

Automated summary

Ring defects in n-type silicon wafers grown by the Czochralski method can significantly affect solar cell efficiency, emitting broad defect-related luminescence peak. This study shows that manipulating excitation laser power can achieve consistent injection levels for quantitative comparisons. Additionally, the effects of hydrogenation and phosphorus diffusion gettering on individual deconvoluted peaks of the DRL spectrum were investigated.