High-resolution lattice imaging of cadmium telluride

Abstract

Structure images of a compound semiconductor, CdTe, have been obtained in the [011] projection using 120 kV transmission electron microscopy. Image spots, corresponding to adjacent columns of cadmium and tellurium atoms, have been resolved in the experimental images, the observed separation being slightly larger than the true resolved atomic separation of 1.62 Å. Also, an intensity difference between the spots corresponding to the two atomic species is noted. Image calculations based on the Bloch-wave formulation indicate that the experimental images can be adequately simulated with 13 beams contributing to the image formation. The possibility of distinguishing between the columns of cadmium and tellurium atoms in the experimental images is examined, with instrumental and specimen parameters used as variables. It is found that the intensity difference is a sensitive function of lens defocus and specimen thickness, and identification of atomic species in the image is possible only when the experimental parameters are accurately known. The image behaviour is more complex than that for elemental semiconductors. The relevance of these findings to the lattice imaging of other compound semiconductors is discussed.