Morphological instabilities during explosive crystallization of germanium films

Explosive crystallization, a self-sustaining transformation of an amorphous phase to a crystalline phase mediated by a thin liquid layer, exhibits three distinct kinetic and morphological regimes in germanium. Dynamics of these growth processes and the resulting morphologies have been examined in detail. Steady-state crystallization velocities were measured as a function of heat loss into the substrate. Dark field optical microscopy, tapping mode atomic force microscopy, transmission electron microscopy, and x-ray diffraction were used to examine the crystallized films. Analyses of the experimental results provide evidence for two distinct processes governing explosive crystallization in limits of high substrate temperature (low heat loss) and low substrate temperature (high heat loss). The low temperature growth mode produces a "scalloped" structure with propagation velocities that monotonically increase with temperature. At high substrate temperatures, the velocity is independent of temperature and a "columnar" pattern with preferred texture is formed.