Improvement of the critical temperature of NbTiN films on III-nitride substrates

Houssaine Machhadani (1) , Julien Zichi (2) , Catherine Bougerol (3) , Stéphane Lequien (4) , Jean-Luc Thomassin (5) , Nicolas Mollard (6) , Anna Mukhtarova (1) , Val Zwiller (2) , Jean-Michel Gérard (1) , Eva Monroy (1)

1 NPSC - Nanophysique et Semiconducteurs
2 KTH - KTH Royal Institute of Technology [Stockholm]
3 NEEL - NPSC - Nanophysique et Semiconducteurs
4 MEM - Modélisation et Exploration des Matériaux
5 LaTEQS - Laboratoire de Transport Electronique Quantique et Supraconductivité
6 LEMMA - Laboratoire d'Etude des Matériaux par Microscopie Avancée

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 (Tc=11.8 K) was obtained on AlN-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-onsapphire, superconducting nanowire single photon detectors were fabricated and tested, obtaining external quantum efficiencies that are in excellent agreement with theoretical calculations.

Mots clés: NbTiN; superconductor; GaN; AlN; single photon detector

Domaines: Science des matériaux [cond-mat.mtrl-sci]; Optique [physics.optics]; Physique Quantique [quant-ph]; Micro et nanotechnologies/Microélectronique; Optique / photonique

Houssaine Machhadani, Julien Zichi, Catherine Bougerol, Stéphane Lequien, Jean-Luc Thomassin, et al.. Improvement of the critical temperature of NbTiN films on III-nitride substrates. Superconductor Science and Technology, 2019, 32 (3), pp.035008. ⟨10.1088/1361-6668/aaf99d⟩. ⟨hal-02013303⟩