Effect of nitrogen doping on microdefects and minority charge carrier lifetime of high-purity, dislocation-free and multicrystalline silicon

Abstract

We studied the effects of Si growth in atmospheres containing N 2 on minority charge carrier lifetime τ using a high-purity, induction-heated, float-zone (FZ) crystal growth method. Ingots were grown with purge gases that ranged from pure argon (99.9995%) to pure N 2 (99.999%). τ was measured as a function of position along the ingots using the ASTM F28–75 photoconductive decay (PCD) method. We found that Ga-doped, multi-crystalline silicon ingot growth in a partial or total nitrogen ambient has a negligible effect on minority charge carrier lifetime and no significant grain boundary passivation effect. Values of 40 μms < τ < 100 μs were typical regardless of ambient. For dislocation-free (DF) growth, the degradation of τ is minimal and τ values above 1000 μs are obtained if the amount of N 2 in the purge gas is below the level at which nitride compounds form in the melt and disrupt DF growth.