The nucleation and growth of Cd1-xZnxTe crystals in a multi-zone vertical Bridgman growth furnace have been observed and measured using in situ eddy current sensor techniques. A two-coil eddy current sensor measured coil impedance changes for multifrequency which were then interpreted using an electromagnetic finite element analysis. The sensor was used to characterize the initial melting of a charge and the subsequent nucleation of solid during solidification. Fully remelted in situ compounded charges were exposed to significant melt superheating and were found to undergo large melt undercoolings (of up to 20 degrees C), spontaneous crystal nucleation and rapid solidification (velocities approaching 60 mm/h which was more than 10 times the furnace translation rate). Post-growth metallography revealed that about 20 mm of polycrystalline solid was formed in this way before recalescence arrested the solidification interface. In partially remelted charges neither undercooling nor unstable growth were observed. These results indicate that eddy current sensors can be used to monitor critical aspects of the vertical Bridgman crystal growth of semiconducting materials and may simplify the implementation of seeded crystal growth concepts in this, and other, semiconductor crystal growth processes.