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. (2012) Characterisation of InAs/GaAs short period superlattices using column ratio mapping in aberration-corrected scanning transmission electron microscopy. Micron, 43 (10 AbstractThe image processing technique of column ratio mapping was applied to aberration-corrected high angle annular dark field (HAADF) images of short period MBE (molecular beam epitaxy) grown InAs/GaAs superlattices. This method allowed the Indium distribution to be mapped and a more detailed assessment of interfacial quality to be made. Frozen-phonon multislice simulations were also employed to provide a better understanding of the experimental column ratio values. It was established that ultra-thin InAs/GaAs layers can be grown sufficiently well by MBE. This is despite the fact that the Indium segregated over 3-4 monolayers. Furthermore, the effect of the growth temperature on the quality of the layers was also investigated. It was demonstrated that the higher growth temperature resulted in a better quality superlattice structure.

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High angle annular dark field (HAADF) image simulations were performed on a series of AlAs/GaAs interfacial models using the frozen-phonon multislice method. Three general types of model were considered-perfect, vicinal/sawtooth and diffusion. These were chosen to demonstrate how HAADF image measurements are influenced by different interfacial structures in the technologically important III-V semiconductor system. For each model, interfacial sharpness was calculated as a function of depth and compared to aberrationcorrected HAADF experiments of two types of AlAs/GaAs interfaces. The results show that the sharpness measured from HAADF imaging changes in a complicated manner with thickness for complex interfacial structures. For vicinal structures, it was revealed that the type of material that the probe projects through first of all has a significant effect on the measured sharpness. An increase in the vicinal angle was also shown to generate a wider interface in the random step model. The Moison diffusion model produced an increase in the measured sharpness with depth which closely matched the experimental results of the AlAson-GaAs interface. In contrast, the measured sharpness decreased as a function of depth in the linear diffusion model. Only in the case of the perfect model was it possible to ascertain the underlying structure directly from HAADF image analysis.

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