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% gall ium was measured over a temperature range from the melting point to 16 50 degrees C by using an improved Archimedean method with modified dip ping procedure to study the influence of impurity doping on density an omaly. Density anomaly with the thermal volume expansion coefficient o f about 8.0 x 10(-4) K-1 has been observed from 1420 degrees C to 1435 degrees C for the pure molten silicon, together with the drasric decr ease in density, regarded as the stage prior to solidification, from t he melring temperature to 1420 degrees C. This anomaly was also observ ed 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 the rmal volume expansion coefficient, which remained about 0.6 x 10(-4) K -1, regardless of the addition of such impurities over 1435 degrees C. Concentration dependence of density anomalies was also investigated u sing the molten silicon doped with 0.1-1.0 at% gallium, showing no sig n of the anomalous temperature coefficient.