P-T-X Phase Equilibrium in the Zn-Te System

Abstract

Subject classification: 64.60.-i; 64.70.Hz; S8.13 P-T-X data are the thermodynamic basis for modeling the crystal growth of materials with controlled stoichiometry. In this paper results of the first direct experimental measurement of the total vapor pressure are reported for three-phase equilibria SLV (solid-liquid-vapor) and VLS (vaporliquid-solid) in Zn-Te, and the P-T projection of the P-T-X phase diagram is constructed. Geometrical analysis of the phase equilibrium showed that three congruent processes are observed in the Zn-Te system: congruent melting (S = L), sublimation (S = V), and vaporization (L = V). All three congruent curves are tangent to SLV. Consequently, all three congruent points are on the Teside of the maximum melting point of ZnTe. The vapor pressure scanning method was applied to determine the maximum non-stoichiometry as a function of the temperature. The solidus volume of ZnTe was shown to be on the Te-side of the stoichiometric plane.A crucial issue for high-quality single crystal growth of non-stoichiometric materials, such as II-VI semiconductors, is the temperature and pressure dependence of the crystal composition. This information is contained in the P-T-X (pressure-temperaturecomposition) phase diagram. For the Zn-Te system, the T-X projection of the P-T-X diagram was constructed by Steininger et al.[1] from DTA data. The P-T projection of this diagram was studied by Shiozawa et al. [2] by visual observation of the melting points of (ZnTe + Te) and (ZnTe + Zn) samples in sealed quartz tubes placed in a twotemperature furnace. Subsequently, Brebrick [3, 4] measured optical absorption of the vapors over Zn-and Te-saturated ZnTe, and Jordan and Zupp [5] calculated the vapor pressure along the liquidus curve in the Zn-Te system and evaluated the solidus of ZnTe.In this paper, the first direct vapor pressure measurements are reported for the Zn-Te system. The P-T projection was constructed and the maximum Zn non-stoichiometry in ZnTe was determined by the vapor pressure scanning method.The total vapor pressure in the Zn-Te system was measured with a quartz Bourdon gauge in the temperature range T 1100 C and pressure up to 760 mm Hg. Precision of the (P, T) measurements was AE0.5 C and AE0.1 mm Hg. The experimental procedure was similar to that described earlier [6,7]. Two-phase (ZnTe + Zn) and (ZnTe + Te) samples were prepared via direct high-temperature high-vacuum synthesis from extra pure elements weighed out to the nearest 5 Â 10 --5 g. The total impurity content in both 1 ) Corresponding

Vapour pressure investigation of CdZnTe

“…Preparation of the samples and vapour pressure measurement procedure was described in detail elsewhere [1][2][3][4]. Special attention was paid to ensure equilibrium conditions for the experiment.…”

“…Detailed study of the P-T-X phase diagram for Cd-Te system and vapour pressure scanning of non-stoichiometry in CdTe has been reported in [1,2]. Results of the vapour pressure measurement and estimates of solubility of the components in ZnTe were presented in [3,4]. Recently [5,6] thermodynamic properties of ZnTe were updated by experimental measurement of low-and high-temperature heat capacity.…”

p–T–x–y phase diagram of the Cd–Zn–Te system

“…Regarding CZT boundary compositions that correspond to CdTe and ZnTe compounds the concepts of the p-T-x phase space and congruent transformations in binary systems Cd-Te and Zn-Te [6][7][8][9] were invoked. However, a description of phase states involving Cd 1−x Zn x Te cannot be reduced to one coordinate of the composition, i.e.…”

“…The phase diagram of the condensed states in the Cd-Zn-Te system [4,5] and p-T-x diagrams of boundary Cd-Zn [7,11], Cd-Te [6][7][8], and Zn-Te [6,7,9] binary systems made it possible to construct a model p-T-x-y phase diagram for the Cd-Zn-Te system. The ternary Cd-Zn-Te system has only one nonvariant peritectic state, VLS C S Z S CZT ; in the p-T projection it is represented by point P CZT .…”

“…2a. On the sides of the T-x-y prism, the T-x projections of the p-T-x phase diagram for the Cd-Zn [7,11], Cd-Te [6][7][8], and Zn-Te [6,7,9] systems are plotted. The regions of homogeneity for the CdTe-and ZnTe-based crystal phases are enlarged.…”