Changes were noted, in the photoluminescence spectra of thin-film samples, which were associated with the diffusion of Cu. The main effects of the latter appeared to be the quenching of a donor-acceptor transition that was associated with Cd vacancies, and an increase in the intensity of a lower energy band due to deep acceptor states. Changes in junction photoluminescence were consistent with the movement of Cu+ ions in electric fields near to CdS/CdTe junctions.

Photoluminescence Study of Cu Diffusion and Electromigration in CdTe D.Grecu, A.D.Compaan: Applied Physics Letters, 1999, 75[3], 361-3

Figure 13

Diffusivity of Cu in CdTe