Sammendrag
In this work, the effect of the concurrent presence of B and P on bulk material properties of directionally solidified compensated Solar Grade Silicon (SoG-Si) ingots has been investigated. Two ingots have been directionally solidified in a silica crucible from 100% compensated SoG-Si feedstock produced by Elkem Solar. The initial B and P content prior to the directional solidification experiment was 1260 ppba and 762 ppba, respectively. Two reference ingots have been solidified in a silica crucible from 100% EG-Si feedstock, with 332 ppba of boron. The four ingots have been cast under similar process parameters. The resistivity measurements by Four Point Probe (FPP) are in good agreement with the net dopant content, i.e. NA-ND for p-type material, measured by Glow Discharge Mass Spectrometer (GDMS). Bulk lifetime measurements show a decrease in the values compared to the EG reference. Lifetime distributions show the highest values of 13 and 19 µs at approximately half ingot height, compared to 30 and 44 µs in the reference ingots. This decrease can be due to the concurrent effect of compensation and of other impurities present in the ingot. However, the content of several transition metals measured by GDMS at half ingot height was not significantly higher than that of the reference ingots. Oxygen content as measured by Fourier Transformed Infra-Red (FTIR) spectroscopy show no significant difference compared to the references.