Effect of Cooling Rate during Thermal Processes on the Electrical Properties of Cast Multi-Crystalline Silicon

Abstract

Photoluminescence PL imaging techniques and the minority carrier lifetime test system were employed to investigate the variation of the interstitial iron (Fe i ) concentration, the recombination activity of structural defects and the minority carrier lifetime of cast multicrystalline silicon (mc-Si) in response to the cooling rate after heating. The results showed that when the mc-Si wafers are heated to hightemperature (1000 °C) and then cooled to ambient temperature with different cooling rate, the Fe i concentration, the number of recombination active dislocations and grain boundaries increased as the cooling rate rises while the minority carrier lifetime decreased. If cast mc-Si is heated followed by faster cooling at 30 °C/s, the Fe i concentration increase by 223% and the electrical activity of grain boundaries, dislocations and intragrain increase signi cantly, that is to say, the whole wafer is heavily contaminated with metal impurities, and present extremely low minority carrier lifetime.

Multicrystalline, Highly Oriented Thick‐Film Silicon from Reduction of Soda‐Lime Glass

“…However, the solubility of iron in silicon at the temperature of the CSS process is six orders of magnitude lower than that of Al, [ 27 ] and it is much lower than the total Fe concentration of 3.9 × 10 14 cm −3 incorporated in cast mc‐Si as the dominant PV material. [ 30 ] Unfortunately, the SIMS of Al‐doped silicon is affected by a mass interference of the used marker ion ( 54 Fe + isotope) with sputtered Al 2 + molecules. Thus, calculated concentrations of 1.5 × 10 16 cm −3 of Fe in the depth range from 1.5 to 6.5 µm represent an upper estimate.…”