Oxygen distribution on a multicrystalline silicon ingot grown from upgraded metallurgical silicon

Oxygen precipitation creates centers of recombination of carriers. Therefore, oxygen concentration and its chemical configuration must be controlled. In this study, the oxygen distribution on a multicrystalline silicon ingot produced by directional solidification of upgraded metallurgical silicon is investigated. The highest amount of oxygen was detected close to the bottom of the ingot. Most of the oxygen present was interstitial but there were approximately 5–10 ppma oxygen present as precipitates. FT-IR and TEM confirmed the presence of many oxygen precipitates, mainly segregated at grain boundaries and dislocations. Lifetime measurements by QSSPC were performed on as grown- and passivated wafers, and after P-gettering. A correlation between the lifetime values and the presence of oxygen precipitates has been found and it has been shown that the electrical properties could be improved if an appropriate annealing step would be applied. Oxygen content may dramatically reduce the solar cell performances and efficiencies (estimated reduction of 1–3% absolute values).