Influence of undercooling on solid/liquid interface morphology in semiconductors

Highly pure Si and Ge were undercooled by an electromagnetic levitator combined with a laser heating unit. Their crystal growth velocities were measured as a function of undercooling and the appearance of the solid/liquid interface was observed by means of a high-speed camera. The result was compared with the predicted value based on the dendrite growth theory. The growth behavior of Si was found to be classified into three categories of lateral growth, isolated dendrite growth and closer dendrite growth at low, moderate and high undercooling values, respectively. The first transition in the classification was caused by a change in the growth mechanism from stepwise growth in a single plane to that in multiple planes. The second transition was observed as a flattening of the macroscopic appearance of the interface. The transition undercoolings for the classifications were 100 and 210 K for Si, and 85 and 170 K for Ge.