Fundamentals of the CdTe and CdZnTe crystal growth

Robert Triboulet 

CNRS, Laboratoire de Physique des Solides et de Cristallogenese, 1 Place Aristide Briand, Meudon F 92195, France

Abstract

The characteristics of the Cd and Te atoms make the Cd-Te chemical bond of iono-covalent nature with a pretty high ionicity of 0.55 that conditions most of the properties of CdTe and even its growth. As a result of this iono-covalent bond, a sharp liquidus compared to III-Vs, a wide homogeneity range (some 1018 cm-3), a retrograde solidus shape, a low thermal conductivity and pre-transition phenomena are as many severe obstacles having a strong influence on the melt growth of CdTe and making it difficult to obtain large crystals of high quality. That is why just about all the techniques of growth of semiconductor materials have been applied to CdTe!
It has also to be pointed out that CdTe is now replaced, for most and perhaps all the applications it gives rise to, by CZT which possesses very specific properties beside CdTe. At macroscopic scale, the CdTe lattice is strengthened by the incorporation of Zn but at microscopic scale, the very strong repulsive mixing enthalpy in the solid leads to a miscibility gap for temperatures below 428C, as theoretically predicted and experimentally verified both in thin films and bulk crystals. Furthermore, the presence of Zn leads to segregation during Bridgman growth of the alloy which strongly affects the crystal growth, adds a difficulty to the control of stoichiometry during the growth process and leads to the appearance of severe strains in the crystals, at the origin of macro-defects like grain boundaries. Different ways have been used to overcome this segregation: the simultaneous control of both Cd and Zn vapor pressures during the growth process, the use of a replenishing melt and crucible or the use of THM with particular composite source material geometry.
After discussing all these aspects, the most recent achievements in the growth of CdTe and CZT will be presented and discussed.

 

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Presentation: invited oral at NATO Advanced Research Workshop, by Robert Triboulet
See On-line Journal of NATO Advanced Research Workshop

Submitted: 2004-08-10 22:08
Revised:   2009-06-08 12:55