Deposition and characterization of Ge–Sb–Te layers for applications in optical data storage

Ge–Sb–Te films for optical data storage applications were deposited by magnetron sputtering of separate Ge, Sb, and Te targets on Si(1 1 1) wafers in a dc argon plasma. To investigate the influence of the chemical composition of the phase change material on its optical properties, films with lateral compositional gradients of up to 30 at.% were deposited. The composition and structure of the films were investigated by X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA) and X-ray diffraction (XRD) on plain Si wafers, whereas the phase change velocity of Ge–Sb–Te as a re-writable optical data storage medium was determined on Si/Al/SiO2/Ge–Sb–Te multilayers near to technical conditions. The phase change of Ge–Sb–Te films was induced and characterized with a static tester consisting of an optical microscope with an integrated high power laser diode. The change in reflectivity induced by the laser pulses was measured by a high sensitivity photodetector. Depending on the composition, the crystallization time was determined between 220 and 500 ns, while the amorphization time was between 20 and 120 ns.