Effect of Impurity Doping on Density Anomalies in Molten Silicon

The density of molten silicon doped with 0.1 at% boron or 0.1 at% gallium was measured over a temperature range from the melting point to 1650° C by using an improved Archimedean method with modified dipping procedure to study the influence of impurity doping on density anomaly. Density anomaly with the thermal volume expansion coefficient of about 8.0×10-4 K-1 has been observed from 1420° C to 1435° C for the pure molten silicon, together with the drasric decrease in density, regarded as the stage prior to solidification, from the melring temperature to 1420° C. This anomaly was also observed in 0.1 at% boron-doped silicon melt, but completely suppressed in 0.1 at% gallium-doped melt. No change was observed, however, in the thermal volume expansion coefficient, which remained about 0.6×10-4 K-1, regardless of the addition of such impurities over 1435° C. Concentration dependence of density anomalies was also investigated using the molten silicon doped with 0.1-1.0 at% gallium, showing no sign of the anomalous temperature coefficient.