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/sub 2/ on minority charge carrier lifetime /spl tau/ using a high-purity, induction-heated, float-zone (FZ) crystal growth method. Ingots were grown in ambients that ranged from pure argon (99.9995%) to pure N/sub 2/ (99.999%). /spl tau/ was measured as a function of position along the ingots using the ASTM F28-75 photoconductive decay (PCD) method. We found that Ga-doped, multicrystalline 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 /spl mu/s</spl tau/<100 /spl mu/s were typical regardless of ambient. For dislocation-free (DF) growth, the degradation of /spl tau/ is minimal and /spl tau/ values above 1000 /spl mu/s are obtained if the amount of N/sub 2/ in the purge gas is below the level at which nitride compounds form in the melt and disrupt DF growth.