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Epitaxial Growth of Sputtered Ultra-Thin NbN Layers and Junctions on Sapphire

Epitaxial Growth of Sputtered Ultra-Thin NbN Layers and Junctions on Sapphire,10.1109/TASC.2009.2019243,IEEE Transactions on Applied Superconductivity

Epitaxial Growth of Sputtered Ultra-Thin NbN Layers and Junctions on Sapphire   (Citations: 5)
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High crystalline quality of ultra-thin NbN layers and of NbN-MgO-NbN tri-layers, epitaxially grown by DC-magnetron sputtering in the superconducting B1-cubic phase has been achieved in a reproducible way on three different orientations of sapphire substrates i.e. R-, A- and M-planes. Significant improvements such as higher Tc, higher Jc and lower resistivity have been obtained by growing un-twined (110) oriented NbN layers on M-plane orientation of sapphire. Uniform, low roughness, 3-5 nm thick films with Tc above 12 K and Jc above 5 MA/cm2 at 4.2 K were obtained. Characterizations by TEM, AFM and X-Ray diffraction evidence that growth of un-twined NbN on M-plane lead to a better epitaxy in comparison with twinned films observed on other sapphire orientations. We observe that the reduction of the substrate temperature from 600degC to 300degC during the deposition of NbN or NbN-MgO-NbN layers thicker than 20 nm prevents the nucleation of the competing HCP NbN phase. Moreover, 1.5 nm thick AlN or MgO over-layers sputtered in-situ prevent ultra-thin NbN films degradation through aging. The formation of Nb2NyO5-x ( ~ 2.2 nm) at the unprotected NbN surface and of interfacial NbO ( ~ 0.7 nm) native oxides has been observed by XPS. It is forecasted that such improvements in ultra-thin NbN films deposited uniformly on 3 and 4 inch sapphire wafers is a key in the future development of superconducting single photon detectors, THz HEB mixers and also in low noise quantum analogical and digital Josephson devices.
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    • ...As Nb layers are good quality, 10 nm thick Nb (110) layers have been used in some case as template of NbN layers [19]...
    • ...A [Log R-Log T] plot gives a power law value which can be correlated to the nitride phases composition and to excess of nitrogen in the films [12], [13], [19]...

    J.-C. Villegieret al. Integration of Planarized Internally-Shunted Submicron NbN Junctions

    • ...More details on the technique can be found in [7]...

    C. Z. Antoineet al. Characterization of Field Penetration in Superconducting Multilayers S...

    • ...NbN is the material of choice thanks to its short coherence length, that allows the realization of ultra-thin films (down to 4 nm) with acceptable superconductive properties K A/cm . Moreover NbN hasveryfastelectron-phononscatteringandthermalizationtime thatallowssub-nsoperation[11].NbNfilmsofthickness5.4nm were deposited on single crystal M-plane sapphire substrates at...

    Sergio Paganoet al. Nano-Strip Three-Terminal Superconducting Device for Cryogenic Detecto...

    • ...To take advantage of the epitaxial quality of NbN grown on Sapphire, it is convenient to deposit the waveguide material upon patterned detectors [9]...
    • ...Epitaxially grown NbN thin films were deposited by DC-magnetron sputtering on R-plane Sapphire substrate as described in [9], to reach thickness of about 4 nm measured by X-Ray reflectivity...
    • ...To avoid NbN oxidation due to substrate heating, a 10 nm thick MgO protecting layer is RF-sputtered [9] on the whole 4-inch wafer after SNSPD full processing including contacts...
    • ...This technique has already been successful for planar NbN, with very low loss and increase, as shown below in Table I. We conclude that the MgO layer slows the NbN degradation in air [9] even during short heating above 200 ...

    Paul Cavalieret al. SWIFTS Waveguide MicroSpectrometer Integrated on Top of a 1D-NbN SNSPD...

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