Improved phosphorous gettering of multicrystalline silicon

The gettering during an emitter diffusion in multicrystalline silicon is improved by adding a low-temperature tail to the standard diffusion. The tail keeps the emitter sheet resistance within the usable range for solar cells. An increase in minority carrier lifetime by a factor ten is obtained. Decrease in recombination activity of grain boundaries and decrease in interstitial iron concentration are mainly responsible for this improved lifetime. The proposed mechanisms for this improvement are: reduction of size of precipitates because of the longer duration, possibly assisted by beneficial changes in thermodynamics and kinetics of the gettering because of the low temperature. (c) 2005 Elsevier B.V. All rights reserved.