THE FRACTAL CHARACTER OF ANNEAL-INDUCED AGGREGATION IN BILAYER FILMS OF THE GE-AU AND GE-AG SYSTEMS

The fractal character of anneal-induced aggregation in three kinds of bilayer films of the Ge-Au and Ge-Ag systems has been studied in this paper: amorphous germanium (a-Ge)/polycrystalline metal (p-metal), heated deposited a-Ge/p-metal, and (a-Ge + p-metal)/p-metal bilayer films. By means of transmission electron microscopy observation, component analysis of X-ray energy-dispersive spectroscopy and the measurement of fractal dimension for the aggregation regions it has been found that the morphology of the anneal-induced aggregation is divided into different types: the snowflake-like aggregation (SA) region, the equiaxial-like aggregation (EA) region and the randomly distributed aggregation (RDA) region. If the annealing temperature is high enough (exceeds the eutectic temperature of the metal-Ge system), interface co-melting and recrystallization (MR) occur in the annealed film. This depends on the metallic properties, those of the a-Ge film (especially on the a-Ge crystallization temperature T(c)), and on the annealing conditions (the annealing temperature T(a) and the annealing time t(a)). The value of the fractal dimension D(f) could serve as a parameter for describing the morphology of the aggregated region: D(f) almost-equal-to 1.7 - 1.85 for the SA region; D(f) almost-equal-to 2 for the EA region; D(f) almost-equal-to 1.7 - 1.85 for the RDA region; D(f) almost-equal-to 2 for the the MR region. The results are discussed in terms of the equilibrium diagrams of the Au-Ge and Ag Ge systems and the relationship between properties of the semiconductor germanium and metals gold and silver.