Characterization of Compound Semiconductors using Aberration-Corrected Electron Microscopy

Epitaxial growth of semiconductor materials presents many obvious challenges. In addition to preparation of the substrate surface and careful attention to the growth conditions, there are several additional obstacles for heterovalent structures based on two (or more) dissimilar materials. As well as lattice mismatch, which inevitably leads to strain and likely defect formation, valence mismatch and differences in thermal expansion, are further factors that can seriously impact the eventual epilayer quality. The transmission electron microscope has a wide range of imaging, diffraction and analytical techniques that can provide invaluable information about the often-competing effects of growth conditions and compositional differences. The development of aberration correction has enabled electron microscope information limits to be extended beyond the 1-Å resolution barrier, and makes it (almost) routine to achieve atomic-resolution imaging from many different types of materials. For elemental and compound semiconductors it is even possible to resolve the projections of individual atomic columns, often referred to as dumbbells, in the common <110> projection. Composition profiles across heterovalent interfaces, as well as bonding information at the atomic level, can also be achieved when using the probe-corrected configuration. The challenge for the electron microscopist is to utilize these enhanced capabilities to provide useful constructive feedback to the growers responsible for materials growth. In this talk, recent studies of II-VI/III-V, IV-IV, and III-nitride heterostructures using aberration-corrected electron microscopy will be described.