Elastic properties and lattice thermal conductivity of amorphous Ge2Sb2Te5 and GeTe thin films

Abstract

This study reports on the elastic properties and the lattice thermal conductivity of amorphous Ge2Sb2Te5 and GeTe thin films using surface Brillouin scattering. It is demonstrated that this method allows for the determination of the isotropic elastic constants from the measured surface acoustic phonon frequencies. We found elastic constants of C11=48.7/43.6 and C44=14.3/9.4GPa for GeTe and Ge2Sb2Te5, respectively. These results suggest acoustic hardening in GeTe compared to Ge2Sb2Te5 films, and this was supported by the derived, shear, and Young's moduli. The measured longitudinal and transverse velocities were used to determine the lower limit of the lattice thermal conductivity. In general, both chalcogenides alloys exhibit low lattice thermal conductivities of κmin<0.50Wm−1K−1. This could be beneficial for thermal management in phase-change memory devices and for thermoelectric application.