Performance of Ge-Sb-Bi-Te-B recording media for phase-change optical disks

We investigated the physical properties of GeSbBiTeB materials and examined the feasibility for phase change recording. The studied compositions were Ge4Sb0.5Bi0.5Te5 and Ge2Sb1.5Bi0.5Te5 with B doping. The coexistence of Bi and B atoms into both Ge4SbTe5 and Ge2Sb2Te5 lattice maintains single fcc s tructure without phase separation. The Bi substitution shows benefits in de creasing crystallization temperature and activation energy, however the ref lectivity is slightly reduced.) With small amount addition ofboron about 1 at.%, the reflectivity can be increased.(2)) Conventional 4-layer structure of digital versatile disk-random access memory (DVD-RAM) 2.6 GB format was used to prepare the disks for dynamic characterization and overwrite cycla bility evaluations. The disk with Ge4Sb0.5Bi0.5Te5(B) recording layer shows large noise fluctuation and low overwrite erase ratio, suggesting that the crystallization speed is still insufficient. While the disk with Ge2Sb1.5B i0.5Te5(B) recording layer shows lower writing and erasing powers, stable n oise level and high overwrite erase ratio, indicating the capability for DV D-RAM applications. The effect of B doping was verified to enhance the sign al amplitude and modulation.