Structure and growth mechanisms in thin epitaxial PbTe films

Thin (100–1500 Å) epitaxial PbTe films evaporated in a vacuum on the (100) plane of a single crystal of NaCl were investigated. The films were deposited using both the conventional evaporating system and the hot-wall system. The structure of the films was studied by transmission electron microscopy. The films were obtained at substrate temperatures ranging from 20 to 360°C and all had single crystal structures with the (100) plane parallel to the substrate. Intensive nucleation was observed on surface defects. The influence of the substrate temperature on the character of the nucleation process was studied. In addition, the shape, size and density of the crystallites and their dependence on the substrate temperature were examined. The number of defects and the degree of crystalline perfection of the films depend on the temperatures of the substrate and the hot wall. The films obtained in the hot-wall system were more homogeneous with depth and were less defective than those obtained in the conventional system. From the temperature dependence of the density of nuclei under saturation conditions the activation energy E for the nucleation process was found to be 0.30±0.05 eV.