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Germanium supersaturation during the crystallization of amorphous Te–Ge–Sn thin films

Published online by Cambridge University Press:  31 January 2011

M. Libera ,
M. Chen  and
K. Rubin
M. Libera
Affiliation:
IBM Research Division, Almaden Research Center, San Jose, California 95120–6099
M. Chen
Affiliation:
IBM Research Division, Almaden Research Center, San Jose, California 95120–6099
K. Rubin
Affiliation:
IBM Research Division, Almaden Research Center, San Jose, California 95120–6099
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Abstract

The structure and phase relations of Te–Ge–Sn thin films are examined with application to erasable optical storage media. Free energy data from the literature predict that the region of the Te–Ge–Sn phase diagram between Ge, Sn, and the TeGe–TeSn pseudobinary consists of one two-phase field [α–Ge and Te50 (GexSn1−x)50] and one three-phase field (α–Ge, β–Sn, and TeSn). Electron diffraction from five different Te–Ge–Sn films annealed at 623 K experimentally confirms this prediction. One composition from the two-phase field is deposited as a tri-layer film with the structure 150 nm SiO2/75 nm Te36.3Ge47.4Sn16.3/150 nm SiO2 on a grooved disk substrate, and the microstructure resulting from low-power (12 mW) CW and higher-power (∽50 mW) pulsed laser exposure is studied by transmission electron microscopy and electron diffraction. Of particular significance is that laser-induced crystallization produces a single-phase structure consisting of the Te–Ge–Sn compound phase which is supersaturated with respect to the excess Ge. This supersaturation leads to a disordering of the equilibrium NaCl-type structure of this phase. Crystallization of a micron-sized amorphous spot on a ∼200 ns time scale occurs by a diffusionless process. The fast erase times required by a phase-change optical recording application can thus be achieved in off-stoichiometric compound compositions by way of a nonequilibrium crystallization process.

Type
Articles
Information
Journal of Materials Research , Volume 6 , Issue 12 , December 1991 , pp. 2666 - 2676
Copyright
Copyright © Materials Research Society 1991

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