TY - JOUR
T1 - Germanium supersaturation during the crystallization of amorphous Te-Ge-Sn thin films
AU - Libera, M.
AU - Chen, M.
AU - Rubin, K.
PY - 1991/12
Y1 - 1991/12
N2 - 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 [a-Ge and Te50 (GexSni x)50] and one three-phase field (a-Ge, /?-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 Si02/75 nm Te363Ge47.4Sn16.3/150 nm Si02 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.
AB - 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 [a-Ge and Te50 (GexSni x)50] and one three-phase field (a-Ge, /?-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 Si02/75 nm Te363Ge47.4Sn16.3/150 nm Si02 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.
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U2 - 10.1557/JMR.1991.2666
DO - 10.1557/JMR.1991.2666
M3 - Article
AN - SCOPUS:21544435811
SN - 0884-2914
VL - 6
SP - 2666
EP - 2676
JO - Journal of Materials Research
JF - Journal of Materials Research
IS - 12
ER -