In Situ Optical Monitoring of New Pathways in the Metal-Induced Crystallization of Amorphous Ge

We use high-resolution optical microscopy to characterize in situ the processes at play during the Al-induced crystallization of amorphous Ge. In addition to the well-established aluminum-induced layer exchange (ALILE) process, we demonstrate the existence of another crystallization mechanism with different kinetics and spatial extension using in situ monitoring. Further, ex situ characterizations show that both processes are active in our samples. The ALILE process is found to create a single Ge layer and 111-oriented crystallites in our growth conditions, while the other crystallization process yields a double Ge layer with mixed 111 and 100 orientations in the bottom layer, while the top layer remains amorphous. This work underlines the importance of in situ monitoring for the understanding and modeling of metal-induced crystallization.