Hg-Cd-Te ternary

A significant portion of the thermodynamic data for this system consists of the partial pressures of Hg, Cd, and Te2 PHg, PCd, and P2, respectively, and quantities derived from these. The equations used to represent the vapor pressures of the elements are 

At high pressure Hg(g) is nonideal. Using the equation of state given by Sugawara and Sato (1962), the chemical potential or fugacity / are given by 

The Gibbs energy of formation of CdTe(s) according to the reaction 

In the absence of heat capacity data the enthalpy of formation at the 1092°C melting point is taken as — 30,024 cal/mol and the entropy of formation as —10.346 cal/mol °K. Recent partial pressure measurements by Su et al. (1981) establish the enthalpy of fusion of HgTe(s) as 8727 cal/mol and give 

The enthalpy and entropy of formation at the melting point are calculated from Eq. (127) using standard thermodynamic formulas. 

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Hg Cd Te is an example of a ternary detector, in which the value of x controls the cutoff wavelength. Photoconductive detectors are generally simpler to couple to low noise amplifiers photodiodes generally have lower power consumption because these have no external bias, and better high frequency performance (15,16). 

In the notation used here, congruently melting, narrow-homogeneity-range compounds form in the A-C and B-C binaries of the A-B-C system. These are, of course, the Ga-Sb and In-Sb binaries for the Ga-In-Sb system and the Hg-Te and Cd-Te binaries for the Hg-Cd-Te system. For these binaries it is desired to apply the auxiliary conditions of Eqs. (16) and (17) as well as fit other experimental data before fitting the liquidus lines and then the ternary data. For this purpose it is necessary to carry the development of the model somewhat further. At the same time some insight into the behavior of the model can be attained. We show this development specifically for the A-C or... 

The calculated liquidus isotherms for the Hg-Cd-Te system in Fig. 28 show that the liquidus temperature is not always a maximum in the HgTe-CdTe pseudobinary section. Figure 38 shows the liquidus surface between this pseudobinary and the Hg-Cd axis in more detail for comparison with ten experimental ternary liquidus points obtained by Szofran and Lehoczky... 

Figure 12. The four ternary phase equilibrium diagrams (a) Hg-Te-0, (b) Cd-Te-0, (c) Hg-Cd-0, (d) Hg-Cd-Te. Tie lines connect pairs of mutually stable phases. (With permission of American Institute of Physics.)...

In MBE, ultra-high vacuum chambers are outfitted with a number of evaporation cells. Each cell has a shutter to control the molecular flux. The molecular beam can be pulsed within 0.1 sec and the growth rate can be controlled within a few A sec f During the growth, the substrate temperature is maintained at ca. 500-700 °C. Atomic species most commonly used include Al, In, Sb, Be, Ge, Se, Te, Cd, Hg, Zn, Mn, Pb, and Si. The most common quantum well electrodes produced by MBE are the III-V semiconductors binary and ternary compounds. Some II-VI quantum well structures have also been prepared. 

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