Structure of the optical phase change memory alloy, Ag–V–In–Sb–Te, determined by optical spectroscopy and electron diffraction

Abstract

The structure of the optical phase change memory alloy, silver–vanadium–indium–antimony–tellurium (AVIST), has been investigated by the methods of optical reflectivity change, Raman spectroscopy, and electron diffraction. In order to identify each phase, Sb, AgSb, AgSbTe, and AgInTe films were also studied. The Raman spectrum of an AVIST thin film annealed at 523 K for 1 h in Ar gas, shows two main broad peaks around 116 and 150 cm−1. These peaks appear to be related to Sb vibration modes in the AVIST alloy, but their relative intensities are reversed for the AVIST films in comparison with those for a Sb film. Furthermore, in AVIST, the peak at 116 cm−1 shifts to lower wave number when the vanadium content is increased from 0.4 to 4.7 at %. The electron diffraction pattern of AVIST alloy indicates that the AgSbTe2 crystalline phase dominates rather than Sb. A model of the structure of AVIST consistent with these observations is proposed.