N concentration effects on structure and superconductivity of NbN thin films

Kalal, Shailesh; Gupta, Mukul; Rawat, R.

doi:10.1016/j.jallcom.2020.155925

Cited by 27 publications

(24 citation statements)

References 41 publications

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“…On the other hand, it has been reported that strain can cause significant sub-lattice distortion in the lattice structure of Nb 3 Sn, and lead to reduction of its superconducting properties, primarily due to changes in the density of states at Fermi surface with a lesser contribution due to change in the phonon spectrum [43]. For superconducting NbN, the situation can be more complex since the lattice parameter can increase continuously with an increase in N concentration due to an expansion and distortion in NbN lattice caused by the interstitial incorporation of N atoms [33]. It has been reported that the lowest Raman peak in δ-NbN due to acoustic phonons shifts to higher frequencies with increasing deviation from stoichiometry [44].…”

Section: Resultsmentioning

confidence: 99%

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Ultrathin epitaxial NbN superconducting films with high upper critical field grown at low temperature

Wei

Roy

Yang

et al. 2021

Materials Research Letters

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Ultrathin (5-50 nm) epitaxial superconducting niobium nitride (NbN) films were grown on AlNbuffered c-plane Al 2 O 3 by an industrial scale physical vapor deposition technique at 400°C. Both X-ray diffraction and scanning electron microscopy analysis show high crystallinity of the ( 111)oriented NbN films, with a narrow full-width-at-half-maximum of the rocking curve down to 0.030°. The lattice constant decreases with decreasing NbN layer thickness, suggesting lattice strain for films with thicknesses below 20 nm. The superconducting transition temperature, the transition width, the upper critical field, the irreversibility line, and the coherence length are closely correlated to the film thickness. IMPACT STATEMENTThis work realized high quality ultrathin epitaxial NbN films by an industry-scale PVD technology at low substrate temperature, which opens up new opportunities for quantum devices.

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Section: Resultsmentioning

confidence: 99%

“…Furthermore, the Tc of NbN films is extremely sensitive on N concentration. As indicated by Kalal et al, both deficiency or excess of N from equiatomic NbN composition could lead to a reduction in T C when reactive magnetron sputtering of Nb target at different partial pressure of N 2 was used to grow NbN films [33].…”

Section: Introductionmentioning

confidence: 98%

Ultrathin epitaxial NbN superconducting films with high upper critical field grown at low temperature

Wei

Roy

Yang

et al. 2021

Materials Research Letters

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“…It may be noted that a large variation in the LP (4.32 to 4.45 Å) of δ À NbN has been observed both in the theoretical [32,33] as well as experimental reports. [24,34] Our recent theoretical study revealed a shrinking of unit-cell volume due to some vacancy defect formations. [25] Though the δ À NbN structure is maintained in both samples, a larger value of LP in HiPIMS-NbN sample may be due to a smaller fraction of vacancy mediated defects.…”

Section: Resultsmentioning

confidence: 99%

“…A strong correlation between ρ n and T C has already been reported and it was shown that samples with higher ρ n have a lower T C . [24] Such a direct correlation between ρ n and T C for a conventional superconductor is not straightforward but often higher ρ n is attributed to the presence of a higher amount of disorder.…”

Section: Resultsmentioning

confidence: 99%

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Study of Niobium Mononitride Thin Films Grown Using High Power Impulse Magnetron Sputtering

Kalal

Kumar

Karmakar

et al. 2021

Physica Rapid Research Ltrs

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Niobium mononitride (NbN) has gained considerable attention because of its superconducting and refectory properties making it a promising material in devices like spin filters, Josephson junctions, superconducting qubits, and transistors especially when combined with other semiconductors and/or magnetic materials. [1][2][3][4][5][6][7] The ease of formation along with a relatively higher superconducting transition temperature (T C > 10 K) and a lower superconducting energy gap (Δ(0) % 3 meV) has made NbN to be one of the most studied superconducting materials for a wide range of applications. [8] Additionally, it has been widely used as an oxidation, wear-resistant layer, and diffusion barrier in protective and hard coatings. [9,10] NbN thin films can be synthesized using different growth techniques such as chemical vapor deposition, [11] ion beam-assisted deposition, [12] reactive direct current magnetron sputtering (dcMS), molecular beam epitaxy, [1] atomic layer deposition, [13] pulsed laser deposition, [14] etc.Among these, the dcMS has been widely used to grow thin films due to its cost effectiveness and the ability to grow uniform thin films. In a typical dcMS process, the plasma is mostly dominated by neutrals and the fraction of ionized species is very small (typically less than 5%). [15] The structural properties of the sputtered films strongly depend on the kinetic energies and ionization state of the impinging atomic and molecular species on the surface of growing films. It is well-known that the low ionization in dcMS process results into a porous and loosely packed microstructure and forms a large density of defects in the grown films. [16,17] To overcome these issues high power impulse magnetron sputtering (HiPIMS) has been developed. [18,19] In the HiPIMS technique, high power pulses are applied to a sputtering target contrary to a constant DC voltage in the dcMS. The use of high power pulses onto the sputtering target results in a large fraction of ionized-sputtered species. In addition, gases that are present in the vicinity of target also get ionized. [20] Earlier experimental and theoretical reports suggest that high ion to neutral ratios during HiPIMS process results into better thin-films' qualities in terms of denser microstructure, smoother surface, and interfaces. [21][22][23] Recent experimental and theoretical results [24,25] suggest that Nb vacancies are the most dominant

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Role of nitrogen partial pressure, deposition rate and annealing on stability of β-W phase

Singh

Gupta

et al. 2023

Appl. Phys. A

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N concentration effects on structure and superconductivity of NbN thin films

Cited by 27 publications

References 41 publications

Ultrathin epitaxial NbN superconducting films with high upper critical field grown at low temperature

Ultrathin epitaxial NbN superconducting films with high upper critical field grown at low temperature

Study of Niobium Mononitride Thin Films Grown Using High Power Impulse Magnetron Sputtering

Role of nitrogen partial pressure, deposition rate and annealing on stability of β-W phase

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