Transmission electron microscopy observations of Cu-induced directional crystallization of amorphous silicon

By annealing at 500°C for 1h with an electric field of 180V∕cm, a Cu-deposited a-Si/glass sample undergoes a partial crystallization of amorphous Si, whose microstructure is characterized by conventional and high-resolution transmission electron microscopy. The Si crystallites grow in the ⟨111⟩ and ⟨211⟩ directions with their {011} planes parallel to the amorphous Si film surface, assuming a needlelike shape. Copper silicides are not observed at the leading edges of the crystalline Si needles. The growth directions of ⟨111⟩ and the {011} surface plane orientations are accepted to arise from elastic anisotropy of c-Si and can be explained by considering the strain energy under the uniaxial stress state and the plane stress, equibiaxial strain state. Crystallization behavior of a-Si in the Ni∕a-Si layer is also briefly discussed.