Local structure of amorphous Ag5In5Sb60Te30 and In3SbTe2 phase change materials revealed by X-ray photoelectron and Raman spectroscopic studies

Abstract

Reversible switching between highly resistive (binary “0”) amorphous phase and low resistive (binary “1”) crystalline phase of chalcogenide-based Phase Change Materials is accredited for the development of next generation high-speed, non-volatile, data storage applications. The doped Sb-Te based materials have shown enhanced electrical/optical properties, compared to Ge-Sb-Te family for high-speed memory devices. We report here the local atomic structure of as-deposited amorphous Ag5In5Sb60Te30 (AIST) and In3SbTe2 (IST) phase change materials using X-ray photoelectron and Raman spectroscopic studies. Although AIST and IST materials show identical crystallization behavior, they differ distinctly in their crystallization temperatures. Our experimental results demonstrate that the local environment of In remains identical in the amorphous phase of both AIST and IST material, irrespective of its atomic fraction. In bonds with Sb (∼44%) and Te (∼56%), thereby forming the primary matrix in IST with a very few Sb-Te bonds. Sb2Te constructs the base matrix for AIST (∼63%) along with few Sb-Sb bonds. Furthermore, an interesting assimilation of the role of small-scale dopants such as Ag and In in AIST, reveals rare bonds between themselves, while showing selective substitution in the vicinity of Sb and Te. This results in increased electronegativity difference, and consequently, the bond strength is recognized as the factor rendering stability in amorphous AIST.