6533b829fe1ef96bd128ac8c

RESEARCH PRODUCT

Structure of amorphousGe8Sb2Te11:GeTe-Sb2Te3alloys and optical storage

subject

description

The amorphous structure of ${\text{Ge}}_{8}{\text{Sb}}_{2}{\text{Te}}_{11}$, an alloy used in the Blu-ray Disc, the de facto successor to digital versatile disk (DVD) optical storage, has been characterized by large-scale (630 atoms, 0.4 ns) density-functional/molecular-dynamics simulations using the new PBEsol approximation for the exchange-correlation energy functional. The geometry and electronic structure agree well with available x-ray diffraction data and photoelectron measurements. The total coordination numbers are Ge: 4.0, Sb: 3.7, and Te: 2.9, and the Ge-Ge partial coordination number is 0.7. Most atoms (particularly Sb) prefer octahedral coordination but 42% of Ge atoms are ``tetrahedral.'' Structural details, including ring statistics, local coordination, and cavities (12% of total volume), are strikingly similar to those of ${\text{Ge}}_{2}{\text{Sb}}_{2}{\text{Te}}_{5}$, which is used in DVD--random access memory. The presence of less than 10% Sb atoms leads to significant changes from GeTe.