  We report on an inelastic (Raman) light scattering study of the local
structure of amorphous GeTe films. A detailed analysis of the
temperature-reduced Raman spectra has shown that appreciable structural changes
occur as a function of temperature. These changes involve modifications of
atomic arrangements such as to facilitate the rapid amorphous-to-crystal
transformation, which is the major advantage of phase-change materials used in
optical data storage media. A particular structural model, supported by
polarization analysis, is proposed being compatible with the experimental data
as regards both the structure of a-GeTe and the crystallization transition. The
remarkable difference between the Raman spectrum of the crystal and the glass
can thus naturally be accounted for.
