Crystallisation of amorphous germanium thin films

By combining cross-sectional transmission and scanning electron microscopy with Raman scattering we have investigated the mechanism of nanocrystal formation in ultrathin amorphous Si02/Ge/Si02 trilayers grown by e-beam evaporation as a function of annealing temperature and a-Ge layer thickness. We observe that with decreasing a-Ge thickness the amorphous-to-crystalline (a-to-c) transition occurs at considerably higher temperatures, even avoiding crystallisation for very thin films below 2 nm thickness. Furthermore, we demonstrate that the formation of Ge nano-crystals by annealing at around 900 °C takes place driven by a liquid-mediated mechanism. As indicated by the observed microstructure, the metallic liquid film dewets from the surface forming droplets that upon cooling and under the influence of the Si02 capping layer, solidify into barrel-type nanocrystals. Copyright © 2009 American Scientific Publishers All rights reserved.