Novel TEM methods for large-area analysis of misfit dislocation networks in semiconductor heterostructures

Abstract

Transmission electron microscopy (TEM) is a powerful tool for detailed investigations of individual misfit dislocations and misfit dislocation networks in semiconductor heterostructures. However, the characterization of large numbers of misfit dislocations distributed over large network areas has traditionally been a challenge. Such analyses are important for detailed understanding of phenomena, such as layer mosaicity, that originate from the misfit dislocations, but develop features on a length scale of several tens of microns. Moreover, quantitative interpretations of X-ray diffraction data, based on models that describe the arrangement of misfit dislocations in statistical terms, call for validation by a large-area analysis with microscopic details. In this paper, novel TEM sample preparation and analysis methods are presented, which allow for the efficient study of large numbers of misfit dislocations and provide new insight into the formation of misfit–dislocation networks. The methods discussed are: (i) a double-bevel-polish (DBP) sample preparation for systematic depth-sensitive large-area plan-view TEM imaging of three-dimensional misfit-dislocation networks, (ii) a bevel-polish and cleavage (BPC) sample preparation for efficient large-area Burgers vector analysis of misfit–dislocation networks, (iii) the use of bend contours for large-area plan-view analysis of the Burgers vectors of misfit dislocations in single networks and (iv) the post-growth retrieval of the sequence of dislocation formation by studying antiphase boundaries formed during dislocation glide in layers showing long-range atomic ordering. The feasibility of each method is demonstrated and their potential applications discussed.

Acknowledgements

The author thanks W. Jäger for valuable discussions on the topics of sections 2–4. He further thanks A. Bett and F. Dimroth from the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg for providing the triple solar cell structures used in this work. He acknowledges discussion with J. Schöne on XRD measurements of the In _x Ga_{1− x} As buffer. The study of misfit dislocations in long-range ordered InGaP layers (section 5) was carried out at the IV-Physikalische Institut of the Georg-August-Universität Göttingen. The author thanks W. Schröter and M. Seibt for valuable discussions on this topic. He further acknowledges the provision of the InGaP/GaAs samples by F. Scholz from the University of Stuttgart (now at University of Ulm). The manuscript was written during a stay as a Humboldt fellow at the National Center for Electron Microscopy (NCEM) at the Lawrence Berkeley National Laboratory in Berkeley, California. The author especially thanks U. Dahmen and E. R. Weber for their kind hospitality. He acknowledges financial support by the Humboldt Foundation and by the US Department of Energy under contract number DE-ACO2-05CH11231.