Fractal formalism in crystallized-Ge via Al induced crystallization under ion irradiation

The fractal characterization of polycrystalline-Ge formed via Al induced crystallization under ion irradiation is presented. The polycrystalline (p-) Al (50 nm)/amorphous (a-) Ge (50 nm) is irradiated using 1000 keV Xe⁺ ions with fluences of 7 × 10¹⁴ ions/cm², 3 × 10¹⁵ ions/cm² and 1 × 10¹⁶ ions/cm² followed by post-thermal annealing at 200 °C. The pristine (i.e., as-prepared) sample is also thermally annealed for comparison purposes. The X-ray diffraction measurement confirms the crystallization of Ge after thermal annealing in both pristine and ion irradiated samples whereas only ion irradiation does not show any crystallization of Ge. The optical micrograph and field emission scanning electron microscopy (FE-SEM) images show dotted like structures on the surface of the film which are found to increase with increasing ion fluence. The Rutherford backscattering spectrometry and energy dispersive X-ray spectroscopy confirm the layer exchange phenomena at the interface in the p-Al/a-Ge bilayer system with Ge crystallization. The fractal analyses have been carried out on FE-SEM images which confirms the Ge fractals formation due to crystallization of Ge followed by layer exchange. The fractal dimension and hurst exponent are calculated and found that the surface roughness decreases with increasing ion fluence up to the fluence of 3 × 10¹⁵ ions/cm² and then increases at higher fluence.