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%0 Thesis
%A Khamphasithivong, Felix
%T Development of spin-qubit devices based on ZnSe/ZnMgSe heterostructures
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2024-12284
%P 1 Online-Ressource : Illustrationen
%D 2024
%Z Veröffentlicht auf dem Publikationsserver der RWTH Aachen University 2025
%Z Dissertation, RWTH Aachen University, 2024
%X 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 ≤ 4 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 (ρ<sub>\textc</sub> = 4E-5 Ωcm² 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 (ρ<sub>\textc</sub>  ∼  1.4E-3 Ωcm² 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 ρ<sub>\textc</sub>  ∼  2.5E-3 Ωcm² 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 ≤ 4 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).
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%R 10.18154/RWTH-2024-12284
%U https://publications.rwth-aachen.de/record/999706