Hydrogen-related defects measured by infrared spectroscopy in multicrystalline silicon wafers throughout an illuminated annealing process

Abstract

Hydrogen (H) is thought to be strongly involved in the light and elevated temperature-induced degradation observed predominantly in p-type silicon wafers, but the nature of the defect or defects involved in this process is currently unknown. We have used infrared (IR) spectroscopy to detect the vibrational signatures due to the H-B, H-Ga, and H2*(C) defects in thin, hydrogenated, p-type multicrystalline silicon wafers after increasing the optical path length by preparation and polishing the edges of a stack of wafers. The concentrations of the H-B and H-Ga acceptor complexes are reduced to 80% of their starting values after low intensity (5 mW/cm2) illumination at room temperature for 96 h. Subsequent high intensity illumination (70 mW/cm2) at 150 °C for 7-8 h further decreases the concentrations of these defects; to ∼40% (H-B) and ∼50% (H-Ga) of their starting values. Our results show that, with careful sample preparation, IR spectroscopy can be used in conjunction with other techniques, e.g., quasisteady-state photoconductance, to investigate the involvement of different H-related point defects on degradation in solar-grade silicon wafers.