<title>Ge-Sb-Te system for rewritable optical data storage by a composition-spread approach</title>

Abstract

Because of its fast reversible phase change between a crystalline and an amorphous phase and a corresponding change in optical properties, Ge-Sb-Te alloys are well known as materials for phase change optical data storage [1]. Especially the stoichiometric Ge2Sb2Te5 of the GeTe-Sb2Te3 pseudobinary line is suited for this purpose and already commercially used [2]. Nevertheless, the physical principles of this technique are not yet completely understood. In the presented paper a composition-spread approach was used to deposit Ge-Sb-Te films with compositions around the ternary phase Ge2Sb2Te5. The deposition took place in a UHV sputtering chamber using three magnetron cathodes equipped with pure Ge-, Sb- and Te-targets, respectively, for film deposition. Films were deposited on Si-wafers as well as on Si-Al-5i02 stacks. The resulting composition-spread was analyzed by EPMA-mappings and GI-XRD with respect to composition and structure. The velocity of the phase change was determined using a static tester. The correlation between film constitution and kinetics of the phase change revealed that the change from the initialized crystalline phase to the amorphous phase could be achieved in about 20 ns for optimized compositions. Even slight deviations from this composition resulted in a strong decrease of the phase change velocity. Structural analysis proved the existence of two crystalline phases with cubic and hexagonal structure in the initialized films.