Morphological evolution and structural study of annealed amorphous-Ge films: Interplay between crystallization and dewetting

In this work, the dewetting process of an amorphous-Ge-based thin film (a-Ge) upon annealing has been studied, highlighting the morphological and structural properties of the dewetted islands. By a combination of in-situ reflection high-energy electron diffraction (RHEED) during low and high-temperature annealing and by electron back scatter diffraction (EBSD), the initial crystallization dynamics of the Ge film has been clarified, and the structural characterization of the dewetted islands has been disclosed by high-resolution transmission electron microscopy (HR-TEM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Chemical composition has been assessed by electron energy loss spectroscopy (EELS). Different initial a-Ge film thickness (range: 10 nm-200 nm) and annealing treatments, i.e. annealing temperature in the range between 600 degrees C-820 degrees C, and annealing time in a 5-120 min range, have been investigated to control the dewetting process. Finally, we extended the solid state dewetting process up to 20 cm wafers showing the possibility to tune particles size varying the initial a-Ge thickness of the deposited film, highlighting the scalability of the process. Beyond fundamental understanding of the a-Ge dewetting process, these results are relevant for the fabrication of large-scale hard masters for nanoimprinting lithography and novel photonic platforms fabricated via a scalable, lithography-free, CMOS-compatible process.