PROCESS AND APPARATUS FOR GROWING MERCURY CADMIUM TELLURIDE LAYER BY LIQUID PHASE EPITAXY FROM MERCURY-RICH MELT

摘要

A process and apparatus for growing a layer of mercury cadmium telluride (HgCdTe) on a substrate is used in the fabrication of infrared detectors. The growth of a layer of HgCdTe by liquid phase epitaxy from a melt comprising mercury, cadmium, and tellurium requires a relatively high temperature which causes the mercury to constantly vaporize from the melt, thereby constantly changing the composition of the melt and the HgCdTe layer grown from the melt. This problem is overcome by providing a mercury-rich melt and also by condensing mercury vapors escaping from the melt and returning the mercury to the melt. First, a crystal growth melt (36) comprising mercury, cadmium and tellurium is provided in a vertically-oriented crystal growth chamber (14). The melt (36) comprises 33.33 mole percent or more of mercury and is maintained at a predetermined temperature above the liquidus termperature thereof. A condensing means (such as 15) is provided atop the crystal growth chamber (14) in order to condense vapors of mercury which escape from the melt (36) and to return this condensed mercury to themelt, to thereby maintain the melt at a constant composition. The substrate (not shown) in the substrate holder (22) is contacted with this crystal growth melt (36) for a predetermined period of time while cooling the melt below its liquidus temperature at a predetermined rate sufficient to cause the crystal growth of the layer of HgCdTe on the substrate to a desired thickness. The layer of HgCdTe so formed is of uniform composition and of high purity and is formed at a relatively low growth temperature and relatively low system pressure.