Microstructure and Electrical Properties of Thin Epitaxial Films of PbTe on NaCl

Abstract

Epitaxial thin films of PbTe have been prepared by vacuum evaporation onto the (001) cleavage face of NaCl with substrate temperatures of 100 and 300 °C and deposition rates of approximately 100 and 1000 Å/min, respectively. Electron diffraction showed the films to be strongly oriented with the (001) planes of the deposit parallel to the substrate. Transmission electron microscopy of thinner films, ≈ 0.2μ thick, showed no significant variation in microstructure with changes in substrate temperature and deposition rate. Such films showed a high density of dislocations, ≈ 5×1010/cm2, the majority of which ran normal to the plane of the film. Many were arranged in low-angle grain boundaries, the most prominent microstructural feature of the films. These exhibited rotations up to about 2° and the average boundary spacing for these thin samples was estimated at 2000 Å. Surface replication of a number of films grown with comparable conditions but varying thicknesses show features that could be indicative of internal crystalline boundaries. A decided increase in the spacing of these boundaries with increasing film thickness was noted. dc Hall-effect measurements from room temperature down to 77 °K showed the Hall mobilities exhibited a decreased temperature dependence as compared to that of the bulk. This could be ascribed to the additional scattering influence of the crystal-line boundaries. The spacing of the boundaries was calculated from the electrical data and a comparison with the spacings measured by electron microscopy showed satisfactory agreement.