Structural Changes in Doped Ge2Sb2Te5 Thin Films Studied by Raman Spectroscopy

In this study, we investigated Ge2Sb2Te5 (GST225) amorphous thin films doped with Bi, Sn and In, using Raman scattering spectroscopy, to obtain information about structural changes after doping. Such impurities as Bi and Sn were chosen due to their isomorphism with one of the main components; indium is an active dopant for phase change materials. Two main, most intensive bands appeared at 125 and 153 cm−1 in the spectrum of undoped amorphous GST225 thin film. Additional small bands in the range of 80 cm−1 and near 300 cm−1, which disappeared in Raman spectra of crystalline GST225 thin films, were also observed. The obtained peak parameters were found to correlate with the dopant type and concentration. The concentration dependencies are not monotonic, and this fact indicates different incorporation mechanisms for different dopant levels.