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Improvement of the critical temperature of NbTiN films on III-nitride substrates
Univ Grenoble Alpes, CEA INAC PHELIQS, 17 Av Martyrs, F-38000 Grenoble, France..
KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum and Biophotonics.ORCID iD: 0000-0003-1831-2208
Univ Grenoble Alpes, CNRS Inst Neel, 25 Av Martyrs, F-38000 Grenoble, France..
Univ Grenoble Alpes, CEA INAC MEM, 17 Av Martyrs, F-38000 Grenoble, France..
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2019 (English)In: Superconductors Science and Technology, ISSN 0953-2048, E-ISSN 1361-6668, Vol. 32, no 3, article id 035008Article in journal (Refereed) Published
Abstract [en]

In this paper, we study the impact of using III-nitride semiconductors (GaN, AlN) as substrates for ultrathin (11 nm) superconducting films of NbTiN deposited by reactive magnetron sputtering. The resulting NbTiN layers are (111)-oriented, fully relaxed, and they keep an epitaxial relation with the substrate. The higher critical superconducting temperature (T-c = 11.8 K) was obtained on AIN-on-sapphire, which was the substrate with smaller lattice mismatch with NbTiN. We attribute this improvement to a reduction of the NbTiN roughness, which appears associated with the relaxation of the lattice misfit with the substrate. On AlN-on-sapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD , 2019. Vol. 32, no 3, article id 035008
Keywords [en]
NbTiN, superconductor, GaN, AlN, single photon detector
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:kth:diva-244483DOI: 10.1088/1361-6668/aaf99dISI: 000458129800001Scopus ID: 2-s2.0-85062473569OAI: oai:DiVA.org:kth-244483DiVA, id: diva2:1298046
Note

QC 20190321

Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-05-21Bibliographically approved
In thesis
1. NbTiN for improved superconducting detectors
Open this publication in new window or tab >>NbTiN for improved superconducting detectors
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The physics of single photons is fascinating, by manipulating them we can observe and probe quantum effects. Doing so requires the fabrication and utilization of single photon sources, of which many types have been developed including quantum dots, trapped atoms and ions, and color centers. On the other end of the experiments, single photon detectors play a role of utmost importance, and while several types of detectors exist, superconducting nanowire single photon detectors are now the state-of-the-art technology. By offering near unity detection efficiency from the ultra-violet to the mid-infrared light spectrum, with negligible noise and excellent time resolution, they made possible many experiments that were previously technologically unfeasible. The same appealing characteristics have found a use in applications outside of the quantum optics framework, with notably light detection and ranging, biomedical imaging or CMOS circuits testing.In this thesis a controlled growth method for tailoring the characteristics of niobium titanium nitride in the framework of superconducting nanowire single photon detectors was developed. Reactive co-sputter deposition of niobium titanium nitride was shown to be a versatile method, both in terms of the degree of control over the material composition, and in the choice of substrates that it allows. Unity internal detection efficiency of detectors at telecom wavelengths was achieved by optimizing the niobium content in the material. The influence of lattice matching on the critical temperatures of films deposited at room temperature was investigated. The fabrication of superconducting nanowire single photon detectors on aluminum nitride-on-sapphire, on lithium niobate nano-waveguides, on gallium arsenide, and the integration on SiN waveguides was achieved. The material was used to fabricate detectors with optimized response for any linear polarization of the incoming photons by using a fractal architecture. Another method was proposed to achieve the same results by encapsulating meandering detectors in a high index dielectric material, resulting in a decrease of the permittivity mismatch between the nanowire material and its surrounding and therefore optimizing the efficiency for both orthogonal linear polarizations.Finally, detectors were fabricated from films developed in this work, and were operated to enable the implementation of polarization-based entanglement distribution in optical fibers in a real-conditions scenario, over a record distance of 96 km. This paves the way for the development of quantum communication networks using existing optical fiber links.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. iii-xviii, 66
Series
TRITA-SCI-GRU ; 2019:34
Keywords
superconducting nanowire sngle photon detector, SNSPD, niobium titanium nitride, NbTiN, reactive co-sputtering, quantum communications, quantum sensing
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-251759 (URN)978-91-7873-192-3 (ISBN)
Public defence
2019-06-14, FB42, Roslagstullbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, European Research Council, 307687Swedish Research Council, 638-2013-7152
Note

QC 20190521

Available from: 2019-05-21 Created: 2019-05-21 Last updated: 2019-05-22Bibliographically approved

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Zichi, JulienZwiller, Val

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