Semiconductor materials of Group II-VI elements and especially those containing mercury, cadmium and tellurium are particularly useful as photodetectors for infrared applications. A variety of methods are known for the deposit of crystals of the above elements on substrates and these include: liquid phase epitaxy, elemental vapor phase transport, encapsulated closed-space diffusion, molecular beam epitaxy, and metalorganic chemical vapor deposition (MOCVD), also known as organo-metallic vapor phase epitaxy (OMVPE). The latter method is a most convenient and practical method for producing high quality epitaxial films. However, it has not been very successful in the case of mercury, cadmium, tellurium compounds due to the high temperature required for the decomposition of dialkyltellurium compounds. An important detrimental consequence of high temperature growth of epitaxial tellurides, such as for example HgCdTe, is the diffusion of high vapor pressure metals such as mercury and cadmium at crystal interfaces resulting in poor product quality. Additional detrimental effects are increased consumption of high purity mercury and generation of toxic mercury waste. In one attempt to minimize this problem, Jackson, U.S. Pat. No. 4,439,267, directs a mixed stream of diethyltellurium and dimethylcadmium to impinge on a CdTe substrate which is placed on a graphite susceptor which also contains a pool of mercury placed in a specially constructed cavity. The susceptor is heated differentially to allow decomposition of the metal alkyls and vaporization of mercury, respectively, to occur at two different temperatures, such as for example 400.degree. C. and 200.degree. C. This process, however, is quite complex and difficult to control. Another approach is that disclosed by Hoke et al., U.S. Pat. No. 4,568,397, in which the mercury is vaporized in an externally heated warm zone and transported to the substrate in a vaporized state, the apparatus requiring a source of heating, e.g., a battery of infrared lamps to maintain the mercury vapor at a temperature above 240.degree. C. to prevent condensation prior to reaching the substrate, the reaction ultimately being carried out at about 400.degree. C., a temperature which is required by the difficulty of decomposing the Group VI metalorganic employed, diethyltellurium. In a recent approach, diisopropyltellurium was used instead of diethyltellurium and epitaxial films of CdTe and HgCdTe were grown at the somewhat lower temperature of 350.degree. C. as described by Hoke et al., Appl. Phys. Lett. 46 (4) 396 (1985). However, even at this temperature cadmium/mercury interdiffusion is still a problem especially in the production of HgTe,CdTe superlattices, which are composed of thin, sub-micron, e.g., 40 to 250 Angstroms, alternating layers of HgTe and CdTe. Superlattices of this type which have semiconductor properties superior to HgCdTe epitaxial films cannot easily be made by vapor phase epitaxy and still lower temperatures are needed to prevent metal interdiffusion between layers. The present invention provides an improved method for the vapor phase epitaxial growth of tellurium-containing films and superlattices in that the temperature of reaction is lowered substantially below the levels previously thought to be operative, e.g, 306.degree.-405.degree. C. for CdTe, as described by Schmidt, J. Vac. Sci. Technol. A 3 (1), Jan./Feb. 1985, while still, at temperatures as low as 250.degree. C., providing high growth rates, e.g., of the order of 5 microns/hr., instead of 0.4 microns/hr.
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