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GROWTH AND CHARACTERIZATION OF ALUMINUM EPITAXIAL LAYERS ON INAS QUANTUM WELL STRUCTURES FOR TOPOLOGICAL QUANTUM COMPUTING
thesisposted on 03.05.2021, 10:50 by Tiantian WangTiantian Wang
Superconductor-semiconductor heterostructures is studied for the applications in topo-logical quantum computing. It has been approved that structural quality plays an important role in the application. This thesis focuses on the growth and characterization of Al films on InAs two-dimensional systems. The goal is to generate new knowledge and a complete understanding of the structural properties of the Al films that will lead to higher quality material for further research. The study of aluminum growth orientation and in-plane grain properties are presented.
To study the growth orientation of aluminum, the growth orientation of seven samplesare characterized by cross-sectional TEM analysis and compared with the surface lattice parameter of the semiconductor (Sm) layers (characterized by RSM). A strong dependenceis discovered. Al(111) films are grown on surfaces with a lower lattice parameter (a<5.98Å), while Al(110) films are grown on surfaces with a higher lattice parameter (a>5.98Å).One sample is observed to have an aluminum film with both (111) and (110) orientations. The transition of the growth orientation is related to the residual strain in Al film and the interfacial energy of the Al/Sm interface.
The grain properties of the Al films are studied using plan view TEM analysis. For Al(111) film, the diffraction pattern of plan view sample reveals [−8◦,8◦] in-plane rotation between grains. Clear grain boundaries are observed in dark-field imaging, which leads to an average grain size of 50 nm. For Al(110) film, the diffraction pattern of the plan view sample and the analysis of Al/Sm Moire fringes show the in-plane rotation is [−1.5◦,1.5◦], much smaller than Al(111). The average grain size of Al(110) film is also 50 nm. The difference in in-plane rotation angle reveals the difference in interfacial energy-angle dependence between Al(111) and Al(110) films.