STUDIES ON THE DIFFUSION OF ZINC IN CADMIUM TELLURIDE AT 800-DEGREES-C

The diffusion of zinc into bulk grown cadmium telluride has been studi ed at 800-degrees-C as a function of anneal time and mass of the diffu sion source. The diffusions were carried out in evacuated silica ampou les and the diffusion profiles were measured using a radiotracer secti oning technique, although some measurements were obtained using scanni ng electron microscopy with an EDAX attachment. When the mass of zinc placed in the ampoule exceeded 2 mg, a ternary compound of Zn Cd1-xTe, with x = 0.8, was formed on the surface of the slice early on in the diffusion and the diffusion profiles consisted of two components. Two values of the diffusivity were obtained, D(slow) --> 2 X 10(-11) cm2 s -1 and D(fast) --> 2 X 10(-10) cm2 S-1, for anneal times exceeding 6 h and a mass of zinc of 8 mg placed in the ampoule. This contrasted wit h the results when the mass of zinc was less than 2 mg when no effecti ve surface layer of the ternary compound was formed and diffusion prof iles consisting of a single component were obtained. It is proposed th at two diffusion mechanisms are operating, one due to zinc atoms diffu sing from the vapour into the ZnxCd1-xTe layer and the second an inter diffusion between the ternary compound in the surface of the slice and the CdTe in the bulk.