Crystal growth and growth rates of CdS by sublimation and chemical transport

Abstract

A comparative study of the sublimation and chemical transport of the same compound is reported for the first time. Conditions for nucleation control and growth of large single crystals of CdS in a closed system are investigated both in the case of sublimation and iodine transport. Using the vertical pulling method with iodine transport, controlled nucleation takes place only at iodine concentration lower than 0.2–0.3 mg/cm 3 and critical undercooling. However, if sublimation is used, control of nucleation and growth of conically shaped large single crystals is easily achieved with the same growth method. Conditions are also described for the growth of large single crystals (22 x 10 x 7 mm) on the charge, at undercritical undercooling ( ΔT > 15 °C) so that no nucleation takes place on the quartz walls. High-indexed faces appear in the habit of these crystals. In the presence of iodine the growth rate is diminished, the habit of the crystals is under certain conditions changed and also the critical undercooling is increased. This behaviour is explained as the result of adsorption and a complicated surface reaction.