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

Phase-change optical recording media of the base composition Ge40Sb10Te50 w ith or without boron doping (0.3-1.1 at.%) were prepared by rf sputtering o n Si(100) substrate at a film thickness 100 nm. Crystalline state was obtai ned by subsequent annealing at 300 degrees C for 10 min. The structure stud y of crystallized films showed that lattice parameter of the fee Ge40Sb10Te 50 phase increases slightly with B doping. Crystallization temperature incr eases 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 t he wavelength 350 nm to 38% at 800 nm. With an optimal 0.3 at.% B doping, t he reflectivity contrast exceeds 40% throughout the whole visible wavelengt h range. The distinct changes in refractive index and extinction coefficien t of the Ge40Sb10Te50Bx films due to crystallization is elucidated and foun d to be advantageous in obtaining high reflectivity contrast.