Uphill-Diffusion von Silber in Cadmiumtellurid mit gezielt veränderter Oberfläche

The topic of this thesis is the uphill-diffusion (diffusion from low to high concentration) of Ag in CdTe. Prerequisite for uphill-diffusion is a Te-rich CdTe crystal which, starting from the surface, is gradually transformed into a Cd-rich CdTe crystal. This thesis focuses on the influence of manipulated surfaces of the crystal (i.e. evaporated metal layers or different surface etching procedures). An evaporated Cu layer causes uphill-diffusion of Ag in CdTe. If a structured Cu-layer is used, the structure of the layer can still be observed up to some 100 µm deep within the crystal. The radiotracer method with mechanical polishing was used to determine the con- centration-depth profiles and the lateral distribution of the Ag was observed using auto- radiography. An alternative model to explain uphill-diffusion with evaporated metal layers describes uphill-diffusion as a result of in-diffusing metal atoms displacing the Ag-atoms. To verify this model a radioactive labeled Au-layer and implanted radioactive Ag-atoms were used in an experiment in order to observe both tracers simultaneously. The result doesn’t favor this alternative model. Uphill-diffusion is also observed if the crystal surfaces before implantation are treated by an oxidizing etching process. This is explained by the preferential formation of Te-oxides during the etching process. Therefore a Cd-layer is developed between the oxide layer and the crystal leading to uphill-diffusion. Finally, diffusion parameters for the transition elements Ni and Co were found which result in uphill-diffusion profiles in CdTe. Up to now, this was only observed for the group I elements Ag, Cu and Au.