Optical properties of Ge40Sb10Te50Bx (x=0-2) films

Phase-change optical recording media of the base composition Ge40Sb10Te50 with or without boron doping (0.3-1.1 at.%) were prepared by rf sputtering on Si(100) substrate at a film thickness 100 nm. Crystalline state was obtained by subsequent annealing at 300 degrees C for 10 min. The structure study of crystallized films showed that lattice parameter of the fee Ge40Sb10Te50 phase increases slightly with B doping. Crystallization temperature increases manifestly with minor B addition (10 degrees C at 0.3 at.% B, and 25 degrees C at 1.1 at.% B). The reflectivity contrast between the crystalline and amorphous states of the undoped Ge40Sb10Te50 film ranges from 29% at the wavelength 350 nm to 38% at 800 nm. With an optimal 0.3 at.% B doping, the reflectivity contrast exceeds 40% throughout the whole visible wavelength range. The distinct changes in refractive index and extinction coefficient of the Ge40Sb10Te50Bx films due to crystallization is elucidated and found to be advantageous in obtaining high reflectivity contrast.