The fractal character of anneal-induced aggregation in bilayer films of the GeAu and GeAg systems

Abstract

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 Tc), and on the annealing conditions (the annealing temperature Ta and the annealing time ta). The value of the fractal dimension Df could serve as a parameter for describing the morphology of the aggregated region: Df ≈ 1.7−1.85 for the SA region; Df ≈ 2 for the EA region; Df ≈ 1.7−1.85 for the RDA region; Df ≈ 2 for 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.