Rapid solidification processes of semiconductors from highly undercooled melts

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 by means of two photodiodes and the appearance of the solid–liquid interface was observed by high-speed video camera. The result was compared with the predicted value based on the dendrite growth theory. The growth behaviors of Si and Ge were found to be classified into three categories of lateral, continuous, and successive nucleation at low, moderate, and high undercooling values, respectively in the measured range of undercooling. The transition temperatures for the classifications are 85 and 170 K for Ge. The microstructures of samples solidified from undercooled liquid were investigated and grain refinement showing the successive nucleation is observed.