Reordering Diffusion Processes in Amorphous Thin Films

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Abstract
Germanium and Mg3Sb2 were vapor codeposited on a low‐temperature substrate. The resulting films were amorphous. Subsequent heating to temperatures above room temperature resulted in an ultrafine‐grained structure. Conductance measurements, used to follow the annealing process, indicated two distinct annealing modes. At low temperatures, the conductance decreased on annealing. Somewhat above room temperature, a sudden, almost discontinuous, increase in conductance occurred over a very narrow transition temperature interval. Annealing above this temperature resulted in a gradual increase in conductance. Electron microscope studies indicate that the annealing behavior above the transition temperature interval is associated with extensive grain growth, though below it no structure is observable at all. A study of the annealing behavior below the transition temperature interval by means of conduction measurements indicates an activation energy, for what must be a structural change, of about 0.1 eV. An ordinary diffusion process requires an activation energy an order of magnitude higher. A new mechanism is suggested to account for these observations.