Acceleration of Crystallization Speed by Sn Addition to Ge–Sb–Te Phase-Change Recording Material

Abstract

We have demonstrated that a quaternary Ge–Sn–Sb–Te phase-change recording material obtained by adding Sn to Ge–Sb–Te has a higher crystallization speed than Ge–Sb–Te, and gives a larger erase ratio than Ge–Sb–Te when film thickness is decreased. Static evaluations have shown that a 6-nm-thick quaternary material was crystallized by laser irradiation of 50 ns. Measurements carried out under the conditions of a wavelength of 405 nm, a linear speed of 8.6 m/s and a mark length of 0.294 µm showed that the erase ratio of over 30 dB was obtained with the new composition for a 6-nm-thick layer. A carrier-to-noise ratio (CNR) exceeding 50 dB was also obtained. We think that these effects of Sn addition which give rise to complete crystallization are brought about by abundant nucleation in the amorphous phase even in thin layers. It was confirmed by X-ray diffraction analyses that the new Ge–Sn–Sb–Te material has a single-phase-NaCl-type structure, like the conventional compositions of Ge–Sb–Te.