Effect of aluminum on the solidification kinetics and morphology of gallium

Abstract

The growth rate of (111) face of gallium containing 20, 100 and 1000 ppm aluminum was measured as a function of the interface supercooling and the distance solidified. The experiments were carried out for growth of gallium single crystals contained in gas capillary tubes. It is shown that, similar to the previous results of the dislocation-free growth of high purity gallium, solidification of gallium from the melt occurs by the two-dimensional nucleation mechanism. By comparing the growth rate of the alloys with that of high purity gallium, as a function of supercooling, it is concluded that addition of aluminum increases the two-dimensional nucleation rate, but at the same time decreases the spreading velocity of the steps. The former effect is dominant at small solute concentrations, while the latter becomes important as solute concentration increases. At higher supercoolings, the effect of the solute on the spreading velocity seems to diminish. The growth rate at a constant temperature decreases as a function of distance solidified, which is attributed to the effect of the solute buildup at the interface. The partition coefficient during the faceted growth is estimated to be in the range of 0.001–0.1. As the buildup increases, the faceted interface momentarily breaks down and entraps pockets of the solute-rich liquid. The frequency of the breakdown increases with increasing solute concentration and supercooling, while the size of the liquid pockets decreases with increasing supercooling.