Effect of annealing temperature on the structural and optical properties of amorphous Sb2Te2Se thin films

Thin films of Sb2Te2Se were prepared by conventional thermal evaporation of the presynthesized material on Coming glass substrates. The chemical composition of the samples was determined by means of energy-dispersive X-ray spectrometry. X-ray diffraction studies on the as-deposited and annealed films revealed an amorphous-to-crystalline phase transition. The as-deposited and annealed films at T-a = 323 and 373 K are amorphous, while those annealed at T-a= 423 and 473 K are crystalline with a single-phase of a rhombohedral crystalline structure as that of the source material. The unit-cell lattice parameters were determined and compared with the reported data. The optical constants (n, k) of the investigated films were determined from the transmittance and reflectance data at normal incidence in the spectral range 400-2500 nm. The analysis of the absorption spectra revealed non-direct energy gaps, characterizing the amorphous films, while the crystalline films exhibited direct energy gaps. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.