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@PHDTHESIS{Jalil:909854,
author = {Jalil, Abdur Rehman},
title = {{E}ngineering topological superlattices and their epitaxial
integration in selectively grown hybrid nanostructures via
{MBE}},
school = {RWTH Aachen},
type = {Dissertation},
publisher = {RWTH Aachen University},
reportid = {FZJ-2022-03467},
pages = {309},
year = {2022},
note = {Dissertation, RWTH Aachen, 2022},
abstract = {The realization of advanced spintronics applications
including the topological quantum computation, spin
manipulation for data storage, dissipation less ballistic
transport for ultra-fast quantum devices and topological
switching for low energy memory applications etc. became
more feasible with the experimental discovery of 3D
topological insulators (TIs). The incorporation of exotic
spin-momentum locked Dirac surface states (of 3D TIs) into
these futuristic complex quantum devices requires not only
the growth of high crystal quality epilayers but also the
fabrication of pristine nanostructures, topological band
engineering, ultra-smooth and defect-free surfaces, and
atomically transparent epitaxial interfaces. This work deals
with a systematic study of epitaxial growth of convention 3D
TIs via molecular beam epitaxy(MBE) and atomic-scale
structural characterization via scanning transmission
electron microscope (STEM)to explore the above mentioned
requirements. At first, the relation between the growth
parameters and the defect density in the Van-der-Waals (VdW)
based layered structures is investigated. The optimum growth
parameters are extracted and the defect-free epilayers are
prepared. Later, the technique of selective area epitaxy
(SAE) is explored to develop a platform to achieve a
scalable nano-architecture. Utilizing CMOS compatible
fabrication technology, Si (111) substrates with crystalline
and amorphous combinational surfaces are prepared. The
precisely controlled growth parameters facilitated the
realization of selectively grown topological structure.
Based on statistical analysis, a generalized growth model is
established that provided control over structural defects
through the effective growth rate at the nanoscale and
assisted in achieving high quality nanostructures. Based on
conventional 3D TIs, the capabilities of VdW epitaxy are
exploited further with the growth of topological-trivial
hetero structures. The stoichiometric adjustment in these
hetero structures is utilized as a tool to control the
strength of spin-orbit coupling (SOC) and to engineer the
topological band structure. Two such systems are explored
including BixTey = (Bi2)m(Bi2Te3)n and GST/GBT =
(GeTe)n(Sb2Te3/Bi2Te3)m. With the continuous addition of Bi2
bilayers and GeTe (materials that exhibit trivial phase)
into 3D TIs, the stoichiometric modulations are achieved.
Moreover, the modification of growth parameters is conducted
to incorporate these stoichiometries with the pre-patterned
substrates and selectively grown nanostructures of the
corresponding alloys are prepared. Assisted by the
atomic-scale structural characterizations, the phenomenon of
VdW reconfiguration is explored to observe the
transformation of layer architecture; the key mechanism in
the evolution of interfacial phase change materials
(IPCMs).Moreover, the systematic alterations in the atomic
interaction and resulting changes in bond lengths within a
pristine and hybrid VdW stacks are investigated. The focus
is then shifted towards surfaces where the stability
(inertness) of TI epilayers in the ambient conditions via
structural and compositional investigations, is analyzed. An
undeniable evidence of the aging effect in all material
systems is obtained where a non-saturating oxidation process
at the (0001) surfaces with a continually decreasing
oxidation rate is witnessed. Using the in situ thin film
deposition of Al (2 nm),the top surfaces are passivated and
the aging effect is neutralized. The phenomenon of charge
transfer due to band alignment at the Si (111) - TI bottom
surface is investigated with a comparative growth,
structural and transport analysis of TI epilayer prepared on
HfO2 substrate. Finally, the interfaces between TIs and
various s-wave superconductors (SCs) are explored. The
challenges to achieve the induced superconductivity in TI-SC
hybrid junction and highly transparent interfaces are
addressed. The issue of metal diffusion into the TI epilayer
and the resulting formation of Schottky-like barriers is
avoided with the introduction of a thin metallic film as a
diffusion barrier. Using the natural tendency of transition
metals to transform into their corresponding
di-chalcogenides (TMDCs) at the exposure to TI surfaces,
atomically well-defined and VdW assisted epitaxial
interfaces are engineered. The newly evolved interfaces
assisted in achieving the induced superconductivity that was
a huge limitation in realizing the complex functional
devices.},
cin = {PGI-9},
cid = {I:(DE-Juel1)PGI-9-20110106},
pnm = {5221 - Advanced Solid-State Qubits and Qubit Systems
(POF4-522)},
pid = {G:(DE-HGF)POF4-5221},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2022-06227},
url = {https://juser.fz-juelich.de/record/909854},
}