Profiling Ge islands in Si by large angle convergent beam electron diffraction

Large angle convergent beam electron diffraction (LACBED) is used to profile thin buried Ge layers in Si consisting of islands 100-200 nm across on top of a wetting layer. These studies, tarried out in a FEGTEM using plan-view samples, examine two-beam rocking curves for reflections from planes inclined to the growth direction. A simple measurement of the rocking curve asymmetry is used to profile the net outward displacement across the Ge layer due to lattice mismatch from which the total Ge content is derived. By combining these results with observations on cross-sectional samples giving the Ge layer thickness, the average Ge concentration is derived. The application of the LACBED technique to the profiling of semiconductor strained layers in general is discussed. It is shown that a single atomic layer of Ge in Si should be detectable.