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@PHDTHESIS{Khamphasithivong:999706,
author = {Khamphasithivong, Felix},
othercontributors = {Bluhm, Jörg and Pawlis, Alexander},
title = {{D}evelopment of spin-qubit devices based on
{Z}n{S}e/{Z}n{M}g{S}e heterostructures},
school = {RWTH Aachen University},
type = {Dissertation},
address = {Aachen},
publisher = {RWTH Aachen University},
reportid = {RWTH-2024-12284},
pages = {1 Online-Ressource : Illustrationen},
year = {2024},
note = {Veröffentlicht auf dem Publikationsserver der RWTH Aachen
University 2025; Dissertation, RWTH Aachen University, 2024},
abstract = {Electrostatically defined quantum dots (EDQDs) are a
promising platform for a successful implementation of
universal quantum computing utilizing millions of qubits.
After single and two qubit gate fidelities above the quantum
error correction threshold were demonstrated in isotopically
purified Si quantum wells (QWs), scaling up the qubit number
remains a major challenge [1, 2]. One aspect is linking
distant qubits, as well as realization of an efficient
spin-photon interface that enables linking of quantum
processors [3, 4]. To explore the potential improvement of
ZnSe versus Si as host material for EDQD applications, this
work investigates ZnSe motivated by six promising material
properties: ZnSe is free of nuclear spins if isotopically
purified, it provides a coherent spin-photon interface, it
can be grown defect free, it has no threading dislocations,
it has no valleys and it exhibits a strong spin-orbit
coupling [5-8]. However, ZnSe is an underdeveloped material
platform lacking Ohmic contacts with low resistivity at the
operation temperature of quantum devices ($T\leq4 K$). To
unlock the electrical exploration of the potential of a
proposed EDQD in a ZnSe/ZnMgSe heterostructure, I
investigate electrical contacts including doping, surface
treatment and metallization techniques. By optimization of
the metal-semiconductor interface, I report a record low
contact resistivity ($\rho_{\text{c}}$ = 4E-5 $\Omega$cm²
at 4 K) for Ohmic contacts by all in-situ fabrication
including epitaxial doping, entirely conducted in-house with
our collaboration partners at Forschungszentrum Jülich [5].
Regarding scaling, we modify our approach to locally contact
a ZnSe channel ($\rho_{\text{c}}$ $\sim$ 1.4E-3 $\Omega$cm²
at 4 K), but find this technique incompatible with a ZnSe
QW, facing limits in etch precision. For gated Hall-bar
devices on ZnSe/ZnMgSe heterostructures, observation of the
field effect demonstrates basic device functionality at 4 K.
However, lacking local Ohmic contacts, parasitic effects
presumably originating from planar doping such as parallel
conduction outside the ZnSe QW and recharging of defects
compromises device performance. To avoid performance
limitations originating from planar doping, we develop an
alternative in-situ process well suited to locally contact a
ZnSe QW [9]. Based on selective epitaxial growth utilizing a
shadow mask, our approach yields $\rho_{\text{c}}$ $\sim$
2.5E-3 $\Omega$cm² at 4 K, demonstrated for for a
triangular ZnSe QW. The presented technique enables
exploration of all-electrical ZnSe quantum devices at low
temperature ($T\leq4 K$).[1] X. Xue et al., Quantum logic
with spin qubitscrossing the surface code threshold, Nature
601, 343 (2022).[2] A. Noiri et al., Fast universal quantum
gate above the fault-tolerance threshold insilicon, Nature
601, 338 (2022).[3] D. Awschalom et al., Development of
quantum interconnects (QuICs)for next-generation information
technologies, PRX Quantum2, 1 (2021).[4] K. Wu et al.,
Highly efficient spin qubit to photon interface assistedby a
photonic crystal cavity, Physics and Simulation of
Optoelectronic DevicesXXX, Vol. 11995 (SPIE, 2022).[5] J.
Janßen et al., Low-temperature ohmic contacts to n-znse for
all-electricalquantum devices, ACS Applied Electronic
Materials 2, 898 (2020).[6] K. Sanaka et al., Entangling
single photons from independently tuned semiconductor
nanoemitters, Nano Letters 12, 4611 (2012).[7] A. Pawlis et
al., MBE growth and optical properties of isotopically
purified znse heterostructures,ACS Applied Electronic
Materials 1, 44 (2019).[8] S. Ghosh et al., Internal
magnetic field in thin znse epilayers, Applied Physics
Letters89, 242116 (2006).[9] N. von den Driesch et al.,
Shadow wall epitaxy of compound semiconductors toward all
insitu fabrication of quantum devices, ACS Applied
Electronic Materials 6, 6246(2024).},
cin = {132210 / 130000},
ddc = {530},
cid = {$I:(DE-82)132210_20140620$ / $I:(DE-82)130000_20140620$},
pnm = {DFG project G:(GEPRIS)337456818 - Entwicklung von
Spin-Qubit Bauelementen aus ZnSe/(Zn,Mg)Se Quantenstrukturen
(337456818)},
pid = {G:(GEPRIS)337456818},
typ = {PUB:(DE-HGF)11},
doi = {10.18154/RWTH-2024-12284},
url = {https://publications.rwth-aachen.de/record/999706},
}
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