GROWTH-KINETICS OF SI HEMISPHERICAL GRAINS ON CLEAN AMORPHOUS-SI SURFACES

In solid-phase growth on SiO2 layers of amorphous-Si (a-Si) having clean, native oxide-free surfaces under ultrahigh vacuum conditions, a novel mode of crystallization can be observed: upward growth of Si grains resulting in the formation of nearly hemispherical-shaped grains protruding from the flat surface. Kinetics of the grain growth has been studied by measuring the annealing time and temperature dependence of the hemispherical grain size. The growth behavior is well explained by a model based on the crystallization of surface diffusive atoms supplied only from where the edge of the hemispherical grain contacts the a-Si surface. The activation energy for hemispherical grain growth was found to be 2.3 +/- 0.1 eV from the temperature dependence of the flux density, defined as the number of atoms crystallized per unit time per unit surface area enclosed by the edge. The atomistic mechanism for the hemispherical shape formation and the origin of the activation energy are also discussed.