P–T–X phase equilibrium and vapor pressure scanning of non-stoichiometry in the Cd–Zn–Te system

Technical applications of artificial crystals strongly depend on tailoring the defect structure. In compound semiconductors, native defect concentration is closely related to non-stoichiometry. Vapor pressure scanning (VPS) is a direct high precision method of in situ investigation of the composition of non-stoichiometric crystals at high temperatures. It is based on experimental measurements of the vapor pressure, from which three-dimensional P–T–X (pressure–temperature–composition) range of existence of the crystalline phase is outlined. In this communication VPS data on non-stoichiometry in the Cd–Zn–Te system are presented. Geometrical analysis of the phase equilibrium is performed, and composition of the crystal, melt and vapor is determined in the technologically most important melting region. It will be shown how to apply experimental P–T–X phase equilibrium data for preparation of the material with pre-determined composition, either stoichiometric or with a certain deviation from stoichiometry. Different technologies are analyzed: vapor-phase growth, vertical, horizontal and high-pressure Bridgman. VPS has proved to be a powerful analytical tool. For CdZnTe the accuracy of the VPS determination of non-stoichiometry was shown to be as high as 10⁻⁴ at.% for temperatures up to the melting point.