Ge clustering effects in Ge doped CdTe: electrical and structural properties

High resistivity CdTe can be achieved by introducing impurities that create deep levels which, in turn, control the electronic transport properties of the material via a compensation process. We have characterized the effects of thermal annealing of high resistivity CdTe:Ge under either Te- or Cd-rich atmosphere to understand how modifications in the structure of Ge-related defective states and their electrical activity affect the material transport properties. We have investigated the transport properties with current-voltage analyses, the electrically active deep traps by photoinduced current transient spectroscopy and the local environment of Ge atoms by x-ray absorption spectroscopy. By correlating the modifications observed, we determined the occurrence of Ge clustering effects and associated them to the formation of electrically active deep donor traps, one located at EC-0.31 eV and the other one at midgap, with an activation energy of 0.82 eV.