N-type multicrystalline silicon: A stable, high lifetime material

An investigation of n-type multicrystalline silicon grown by directional solidification has produced several important findings: i) demonstration of effective phosphorus gettering; ii) achievement of minority carrier lifetimes above one millisecond; iii) verification of good stability under illumination. The lifetimes after gettering show a strong dependence on doping: 1.6ms for 2.3cm, 500s for 0.9cm and 100s for 0.36cm, respectively. Lifetime mapping by infrared carrier density imaging has revealed a large surface variability of this parameter, which is detrimental for large area devices. A minor degradation of the lifetime after light exposure has been observed for the highest lifetime regions, while other wafers and regions remained essentially stable.