Optical Properties of Ge₄₀Sb₁₀Te₅₀B_x (x = 0–2) Films

Abstract

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°C for 10 min. The structure study of crystallized films showed that lattice parameter of the fcc Ge40Sb10Te50 phase increases slightly with B doping. Crystallization temperature increases manifestly with minor B addition (10°C at 0.3 at.% B, and 25°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 Ge40Sb10Te50B x films due to crystallization is elucidated and found to be advantageous in obtaining high reflectivity contrast.

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“…The refractive index of the films decreases with increase in thickness with the wavelength in the visible region [26]. This may be due to the transformation of the film from the amorphous to crystalline state [27], which is in good agreement with the structural studies of these films.…”

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