Solidification of highly undercooled Si and Si–Ge melts

We report growth velocity measurements of highly undercooled pure Si and Si–Ge melts (2.5 and 10.0 at.% Ge) processed by containerless electromagnetic levitation. The existence of two regimes of growth for pure Si can be confirmed: faceted growth at low undercoolings and dendritic growth at high undercoolings, separated by a transitional regime. The growth velocity-undercooling relation of pure Si can be reproduced using the Lipton-kurz-Trivedi–Boettinges-coriell-Trivedi dendrite growth model whereas the Si–Ge results show a break in the velocity-undercooling relation. The microstructure of the solidified Si–Ge samples changes from coarse elongated grains at low undercoolings to a fine grained structure at high undercoolings, which can be attributed to the change from faceted to dendritic growth.