Chemical states and optical properties of thermally evaporated Ge–Te and Ge–Sb–Te amorphous thin films

Thin amorphous films of Ge22Sb22Te56 and Ge50Te50 have been prepared from their respective polycrystalline bulk on glass substrates by thermal evaporation technique. The amorphous nature of the films was checked with X-ray diffraction studies. Amorphous-to-crystalline transition of the films has been induced by thermal annealing and the structural phases have been identified by X-ray diffraction. The phase transformation temperature of the films was evaluated by temperature dependent sheet resistance measurement. The chemical structure of the amorphous films has been investigated using X-ray photoelectron spectroscopy and the role of Sb in phase change Ge22Sb22Te56 film is discussed. Survey and core level (Ge 3d, Te 3d, Te 4d, Sb 3p, Sb 3d, O 1s, C 1s) band spectra has been recorded and analyzed. For optical studies, the transmittance and the reflectance spectra were measured over the wavelength ranges 400–2500 nm using UV–vis–NIR spectroscopy. The optical band gap, refractive index and extinction coefficient are also presented for thermally evaporated amorphous thin films.