Finnie, Michael P.
An interfacial study of III-V materials.
PhD thesis, University of Glasgow.
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Z-contrast imaging, using a high-angle annular dark field detector, can be used to characterise III-V heterostructures. GaAs/AlAs heterostructures were grown using MBE and prepared for TEM using a cross-sectional method. SuperSTEM 1 was used to investigate both the GaAs-on-AlAs and the AlAs-on-GaAs interfaces as a function of specimen thickness. The analysis of the images showed that the apparent interface widths varied with thickness in an unexpected manner. The measured GaAs-on-AlAs interface widths remained constant with thickness while the AlAs-on-GaAs interface widths increased. Furthermore, the apparent width of the GaAs layer increased with increasing thickness. The actual interfacial width can be a result of either surface stepping during MBE growth or inter-diffusion of the Type-3 atoms. To assist the interpretation of these results, a series of interfacial models were created and explored using a modified version of the frozen phonon multislice simulation. The models consisted of terraced, vicinal and diffused interfaces. The model results indicate that a diffuse interface can be used to describe the characteristics observed in the experimental images. However, probe scattering from the interfacial region can be counter intuitive. A systematic study of these effects is presented outlining complications that can occur when interpreting interfacial structures using HAADF imaging.
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