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

We use high-resolution optical microscopy to characterize <i>in situ</i> 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 <i>in situ</i> monitoring. Further, <i>ex situ</i> 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 <i>in situ</i> monitoring for the understanding and modeling of metal-induced crystallization.