Thermal conductivity of amorphous vs crystalline Ge and GeTe films

Abstract

Thermal conductivity of amorphous and crystalline Ge and GeTe films has been measured. Both amorphous and crystalline Ge and GeTe films show no thickness dependence for thicknesses >2000 Å. Except for crystalline GeTe films, all other films exhibit no significant electronic contribution. The thermal conductivity of both amorphous Ge and GeTe films increases monotonically with increasing temperature in contrast to the 1/T-dependence of the crystalline films. The observed increase of the thermal conductivity with temperature for amorphous films can be understood primarily in terms of the increase of the specific heat with temperature. The phonon mean free path values calculated from the thermal conductivity data suggest size of the scattering regions (and hence the extent of the short range order) to be ~3 Å in amorphous GeTe, and ~5 Å in amorphous Ge Films.