INITIAL CRYSTALLIZATION STAGE OF AMORPHOUS-GERMANIUM FILMS

The incubation time for the crystallization of amorphous Ge (a-Ge) films was studied as a function of temperature between 150 and 500-degrees-C by means of both in situ transmission electron microscopy and Raman scattering spectroscopy. The temperature dependence of the incubation time for free-sustained a-Ge films follows an Arrhenius curve with an overall (nucleation+growth) crystallization process activation energy of 2.0 eV. In the case where the a-Ge films were on Si3N4 substrates, an earlier stage of the crystallization was observed (nucleation), having an activation energy of 1.3 eV. In addition, it was found that a thin metallic layer of Al or Au, deposited on the a-Ge films, induces a very fast crystallization in the mode of dendritic growth, as reflected by a low activation energy (0.9 eV) for the incubation time temperature dependence.