Dielectric relaxation processes in stoichiometric Ge:Sb:Te amorphous films

The aim of this work is to investigate the relaxation processes of amorphous thin films by dielectric spectroscopy in films with stoichiometric compositions Ge1Sb4Te7, Ge1Sb2Te4 and Ge2Sb2Te5. Experimental results fit well to an empiric Havriliak-Negami model. Two relaxation processes have been observed in all materials: an alpha relaxation in the low frequency range (0.1-10 kHz) and a secondary beta relaxation in the high frequency range (100 kHz-10 MHz). The temperature dependence of the relaxation time for the alpha relaxations is described by the Vogel-Fulcher-Tammann relation with Vogel temperature increasing from 280 K for Ge1Sb4Te7 to 291 K for Ge2Sb2Te5. The secondary beta or Johari-Goldstein relaxation observed in the high frequency range has an Arrhenius-type dependence and approximately the same activation energy 0.422 +/- 0.009 eV for all studied Ge:Sb:Te films. A plausible explanation for relaxation processes observed in Ge:Sb:Te films can be related to cooperative and local rearrangements of molecules or clusters of GeTe and/or Sb2Te3. (C) 2010 Elsevier B.V. All rights reserved.