Photoinduced Crystallization of Sb2Se3 and Ge2Sb2Te5 Chalcogenide Films

The photoinduced crystallization of thin amorphous films based on the binary compound Sb2Se3 and the ternary compound Ge2Sb2Te5 under continuous-wave laser irradiation is studied. The optical parameters of amorphous and crystalline films are analyzed by optical and atomic force microscopies, ellipsometry, spectrophotometry, and Raman spectroscopy. The crystallization temperatures, optical band gaps, Urbach-tail lengths, the activation energies of electrical conductivity, as well as the spectral dependences of the refractive indices and the extinction coefficients, are determined. The crystallized regions of Sb2Se3 are characterized by the more pronounced inhomogeneity of reflectivity (grain size) compared to crystalline regions of Ge2Sb2Te5 produced with the same laser-beam parameters. An analysis of the topography of crystallized films shows qualitative differences in the crystallite sizes. The distinctions may be related to differences in the mechanism of photoinduced crystallization. The Sb2Se3 compound has a higher optical band gap in comparison with Ge2Sb2Te5 and lower absorbance in the visible and near-infrared region, which can reduce the optical losses in the elements of silicon integrated optics based on the phase-change materials, as well as extend the range of possible application of phase-change materials for optical elements and nanophotonics devices.