First-sharp diffraction peaks in amorphous GeTe and Ge2Sb2Te5 films prepared by vacuum-thermal deposition

We report on a presence of intermediate-range order in amorphous GeTe and Ge2Sb2Te5 phase change films prepared by simple vacuum-thermal deposition. We find that thermally deposited GeTe and Ge2Sb2Te5 films show significant first sharp diffraction peaks (FSDPs) in the X-ray diffraction pattern, although the intensities in GeTe and Ge2Sb2Te5 fabricated by sputtering technique have previously been reported to be very small due to their characteristic structures. This is in contrast to the case of strong network forming glasses like As-S(Se) and Ge-S(Se), in which FSDPs are clearly observed both in evaporated and sputtered films. The observed fabrication-dependent intermediate-range structures in the amorphous Ge-Sb-Te system help in exploring the physics of the metastable forms of amorphous semiconductors and the phase change mechanism