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A comparison of the diffusion of copper, gallium and cadmium in cadmium telluride

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Abstract

The rates of diffusion of both Ga and Cu in CdTe have been measured over the temperature ranges 350–820 and 200–400°C respectively and the results are compared with the self-diffusion of Cd (350–920°C).

In the case of the Cd self-diffusion the Arrhenius graph showed two active diffusion mechanisms, one dominating above 500°C and the other below. It suggested that in the temperature range 500–800°C the main defect responsible for diffusion was Cdmath image, with a significant contribution at lower temperatures from the associated defect of the form (CdiVcd)x Below 500°C another mechanism predominated which was possibly due to residual impurities.

The results for the diffusions were in close agreement with those obtained by other workers. The Ga diffusions showed a complex behaviour which suggested that two mechanisms were active simultaneously, one independent of Cd partial pressure and the other decreasing with increasing Cd partial pressure.

It was concluded that CdTe would be suitable as a diffusion barrier to protect HgxCd1 − xTe devices from Ga contamination from GaAs substrates but would not be efficient at reducing Cu contamination from the substrate in the device.

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