Abstract
The annular dark field (ADF) image contrast ofGaNyAs1−y (y = 0.029 and 0.045) epitaxial layers on (100) GaAs substrates was studied with a scanningtransmission electron microscope (STEM) as a function of ADF detector innersemi-angles ranging from 28 to 90 mrad. Contradictory to the compositional contrastprediction of ADF-STEM image intensity, the lower average atomic number strainedGaNyAs1−y layers were found to be brighter than the higher average atomic number GaAs for anADF detector semi-angle up to 65 mrad. Multislice simulations reveal that thedisplacement around substitutional N atoms plays a crucial role in the observedADF-STEM contrast, while the contribution to the contrast due to misfit strain betweenGaNyAs1−y and GaAs is small.
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