Controllable Nitrogen Doping in Multicrystalline Silicon by Casting Under Low Cost Ambient Nitrogen

We have utilized cheaper ambient nitrogen for casting multicrystalline silicon ingots. Ambient nitrogen serves as the N doping source, it causes Si₃N₄ inclusions and related cracks when the doping amount is too high, while N doping can be effectively controlled by tuning the pressure of ambient nitrogen. The maximum value of the N concentration is measured up to 9.4 × 10¹⁵/cm³ by SIMS. The increase of nitrogen concentrations can reduce wafer breakage rate by significantly improving the fracture strength of wafers. The influence of N-O complexes in N-doped MC-Si on electric properties is also discussed. Solar cell efficiencies of N-doped wafers are almost comparable to those from ingots grown under ambient argon.