High Resolution Z-Contrast Observation of GaAs/Si Hetero-Interfaces through Scanning Transmission Electron Microscope

Interfaces of GaAs/Si(100) grown by molecular beam epitaxy were observed through high resolution Z-contrast imaging in a scanning transmission electron microscope. Such images can be interpreted directly, and provide atomic-scale structural and compositional information. Regions of the interface were observed to be faceted on a fine scale with microtwins often threading from these regions into the film. Low-temperature grown buffer layers were found to be very effective for the suppression of defects grown in the epitaxial layer, even in the presence of the interfacial roughness. This suggests that the threading defects are due to the initial three dimensional growth mode and also due to substrate surface contamination. Interfacial misfit dislocations are clearly found to be located in the GaAs film about 5 Å from the interface. The incoherent images combined with compositional contrast provides much improved atomic-scale characterizations of the hetero-structure.