AVS 47th International Symposium
    Thin Films Tuesday Sessions
       Session TF-TuP

Paper TF-TuP36
Mechanism of the Isothermic Amorphous-to-Crystalline Phase Transition in Ge:Sb:Te Ternary Alloys

Tuesday, October 3, 2000, 5:30 pm, Room Exhibit Hall C & D

Session: Poster Session
Presenter: Yu.V. Vorobiev, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
Authors: J. González-Hernández, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
E.F. Prokhorov, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
Yu.V. Vorobiev, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
E. Morales-Sánchez, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
A. Mendoza-Galván, Centro de Investigacion y de Estudios Avanzados del IPN, Mexico
S.A. Kostylev, Energy Conversion Devices, Inc.
Y.I. Gorobets, Kiev Politechnic Institute, Ukraine
V.N. Zakharchenko, Kiev Politechnic Institute, Ukraine
R.V. Zakharchenko, Kiev Politechnic Institute, Ukraine
Correspondent: Click to Email
The kinetics of the isothermic amorphous-to-crystalline (fcc) phase transition at different temperatures has been investigated in alloys with the composition close to Ge@sub 2@Sb@sub 2@Te@sub 5@ which are the most frequently used for erasible optical memory devices. For monitoring the transformation, the electrical resistivity and capacitance measurements were employed as well as the ellipsometry, optical transmission and electron microscopy data. The procedure to determine the transformed volume fraction on the basis of the optical transmission and electrical conductivity data is analyzed. It is shown that the assumption widely accepted about the proportionality between the variation of transmittance or the conductivity and the transformed volume fraction, is seldom correct in the optical case, but never correct in the electrical one; the use of the corresponding procedure could give an error in determination of the crystalline volume fraction of about an order of magnitude. The correct procedure for this case is developed. The transformation kinetics observed agrees with the Johnson-Mehl-Avrami formalism, and gives an average Avrami exponent around 2 and the overall activation energy of about 4.5 eV; the latter value exceeds the previous estimations. The transformation process has the two well-defined stages corresponding to the bulk and surface nucleation of the crystalline phase, the sequence of the stages depends on temperature. It was also found that the ultimate degree of transformation in isothermic experiments is less than 1 and depends upon the transition temperature; the analytical description of this dependence is given. It is shown that this dependence influences the value of the phase transition activation energy determined from the experiment.