The diffusion of Au and its effects on the structural, electrical and optical properties of CdTe films fabricated by using the close-spaced sublimation technique were investigated. The diffusion of Au was studied at 400 to 550C by using energy dispersive X-ray fluorescence analysis. The Au-doped and un-doped CdTe films were characterized by using X-ray diffraction, electrical and optical absorption measurements. The temperature dependence of the diffusion coefficient of Au in CdTe films (figure 5) could be described by:

D (cm2/s) = 4.4 x 10-7exp[-0.54(eV)/kT]

The mechanism of Au diffusion in polycrystalline CdTe films was attributed to the fast migration of Au along grain boundaries, with simultaneous penetration into grains and settling on Cd vacancies. It was proposed that the weak influence of Au diffusion upon the X-ray diffraction patterns of CdTe films could be explained by the dispersal of Au atoms preferentially on Cd vacancies due to the proximity of the covalent radii of Au and Cd. The Au atoms, placed on Cd vacancies (AuCd) during fast cooling from diffusion temperature to room temperature, exhibited an acceptor behaviour; with an energy level of about Ev+0.2eV.

Influence of Au Diffusion on Structural, Electrical and Optical Characteristics of CdTe Thin Films. T.D.Dzhafarov, M.Caliskan: Journal of Physics D, 2007, 40[13], 4003-9

Figure 6

Diffusivity of Au in CdTe