Direct deposition of polycrystalline CdTe films on the Medipix readout chip and evaluation of layer quality and imaging results

Cadmium telluride (CdTe) is used as a photon absorber layer in medical X-ray imaging and radiation detection. Polycrystalline CdTe and a sequence of back contact materials have been directly deposited on the Medipix readout chip as well as on silicon substrates by physical vapor deposition. The whole structure is investigated with respect to the electrical properties of the film sequence. The growth takes place in a modified MBE system allowing CdTe growth rates up to 6 μm/h. Because this process allows evaporation of multiple source materials an entire detector can be assembled by depositing the CdTe absorber layer, followed by a back contact sequence consisting of Te, Sb₂Te₃ and Au/Pt. In order to study composition and quality of the deposited films, optical and scanning electron microscopy as well as X-ray diffraction measurements have been carried out. For electrical characterization resistivity and dark current were determined.