The diffusion of copper in cadmium telluride

Abstract

The diffusion and solubility of Cu in CdTe single crystal material has been measured in the temperature range 200–400°C using a radiotracer sectioning technique. The diffusivity in this temperature range is given by the Arrhenius relationship: D = 6.65 x10 -5 (cm 2 s -1) exp[-0.57 eV/ kT] and the corresponding surface Cu concentration in the diffused CdTe slices is given by the Arrhenius relationship C 0 = 1.56 x10 23 (cm -3) exp[-0.55 eV/ kT]. The addition of Cd or Te to the capsule did not result in profiles that were significantly different to those given by the above expressions and diffusion probably occurred via a defect of the form (Cu iCd v)'. The major portion of the activation energy for the diffusion was taken up in the formation of the defect rather than in its migration through the lattice. A much faster diffusion mechanism (≈100 times faster), which did not show any consistent behaviour with temperature, was also observed in the diffusion profiles. Because of this, CdTe will not act as an effective barrier, in the fabrication of Hg xCd 1− x Te (MCT) infra-red detectors, to prevent Cu diffusing from the substrate through the CdTe buffer layer into the epitaxially grown MCT layer.