Laser ultrasonic sensing of the melting and solidification of cadmium telluride

A noninvasive laser ultrasonic method has been used to investigate the melt ing and solidification of a (Cd,Zn)Te alloy during vertical Bridgman growth . A single zone vertical Bridgman furnace was integrated with a laser ultra sonic system and used to monitor the time-of-flight of ultrasonic pulses th at propagate across an ampoule during the melting and solidification of Cd0 .96Zn0.04Te. The measurement approach is based upon the difference in the e lastic stiffness of the solid and liquid phases of Cd0.96Zn0.04Te (Queheill alt et al., J. Appl. Phys. 83 (1998) 4124) and its significant dependence u pon temperature. This results in a reduction of the longitudinal wave ultra sonic velocity as the temperature was increased (from ambient temperature) followed by a similar to 45% decrease upon melting. The laser ultrasonic se nsor provided a robust in-situ method for monitoring the melting and solidi fication of Cd0.96Zn0.04Te. The data indicated that the melting was slow an d that solidification was accompanied by a 10-15 degreesC undercooling. (C) 2001 Elsevier Science B.V. All rights reserved.