Structural transformations of silver photodoped Ge-Sb-Te thin films

Photodoping of Ag in Ge22Sb22Te56 films has been done by illuminating the thermally evaporated Ag: Ge-Sb-Te bilayer (similar to 40 nm:250 nm) with 500 W halogen lamp. Disappearance of Ag (111) peak in x-ray scan from the bilayer after 20 min. illumination at room temperature confirms the photodoping of Ag in the chalcogenide film. The effects of Ag-photodoping on the optical properties of the Ge22Sb22Te56 film have been examined by transmission and reflection data. The structural phases have been evaluated by x-ray diffraction patterns of thermally annealed films and sheet resistance variation with temperature measurements. It is found that amorphous to crystalline transformation temperature increases and optical gap decreases in Ag-photodoped films. The x-ray diffraction (XRD) has been studied for the films annealed at two different temperatures. Peaks of FCC phases appear in Ge22Sb22Te56 film annealed at 160 degrees C but Ag-photodoped Ge22Sb22Te56 film remains amorphous. The peaks of Ag5Te3 phases are identified for Ag-photodoped Ge22Sb22Te56 film annealed at 250 degrees C.