Phase‐Dependent Oxygen Defect Energetics in Epitaxial NbN/AlN/NbN Films
9 affiliations
- 1Department of Materials Design and Innovation University At Buffalo Buffalo New York USA
- 2Department of Physics and Astronomy Stony Brook University Stony Brook New York USA
- 3Institute For Advanced Computational Science Stony Brook University Stony Brook New York USA
- 4Department of Electrical and Computer Engineering Yale University New Haven Connecticut USA
- 5Department of Materials Science and Engineering Cornell University Ithaca New York USA
- 6School of Electrical and Computer Engineering Cornell University Ithaca New York USA
- 7Kavli Institute at Cornell for Nanoscale Physics Cornell University Ithaca New York USA
- 8School of Applied and Engineering Physics Cornell University Ithaca New York USA
- 9Center For Computational Quantum Physics Flatiron Institute New York USA
Abstract
Epitaxial all‐nitride Josephson junctions are promising components for high coherence superconducting qubits, yet nanoscale defects often limit their performance. The key to mitigating these defects lies in understanding the atomic‐scale relationship between polymorph selection, defect chemistry, and device performance. Here, we investigate structural and chemical defects in epitaxially grown 𝛿‐NbN/AlN/𝛿‐NbN, 𝛾‐Nb4N3/AlN/𝛾‐Nb4N3, β‐Nb2N/AlN/β‐Nb2N heterostructures on c‐plane sapphire using molecular beam epitaxy. Advanced microscopy integrated with density functional theory shows varying impurity distribution across different polymorphs. The chemical distribution reveals that δ‐NbN electrodes contain significant oxygen, whereas in β‐Nb2N/AlN/β‐Nb2N heterostructures oxygen preferentially segregates to the AlN barrier. DFT calculations indicate that these differences arise from phase‐dependent oxygen energetics and diffusion kinetics, with oxygen remaining kinetically trapped in δ‐NbN while exhibiting greater mobility in β‐Nb2N. These structural and chemical differences are consistent with the distinct transport behavior observed in the two junction architectures and provide mechanistic insight into the role of defect chemistry in epitaxial nitride Josephson junctions. The observed impurity distribution may influence superconducting properties and contribute to the formation of two‐level systems, a major source of loss and decoherence in superconducting quantum circuits.
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BibTeX
@article{garg2026phasedependent,
title = {{Phase‐Dependent Oxygen Defect Energetics in Epitaxial NbN/AlN/NbN Films}},
author = {Prachi Garg and Kedarsh Kaushik and Danqing Wang and Naomi Pieczulewski and Anand Ithepalli and John Wright and Debdeep Jena and David A. Muller and Hong X. Tang and Cyrus Dreyer and Baishakhi Mazumder},
journal = {Advanced Science},
year = {2026},
month = aug,
doi = {10.1002/advs.76944},
url = {https://doi.org/10.1002/advs.76944},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Phase‐Dependent Oxygen Defect Energetics in Epitaxial NbN/AlN/NbN Films
AU - Prachi Garg
AU - Kedarsh Kaushik
AU - Danqing Wang
AU - Naomi Pieczulewski
AU - Anand Ithepalli
AU - John Wright
AU - Debdeep Jena
AU - David A. Muller
AU - Hong X. Tang
AU - Cyrus Dreyer
AU - Baishakhi Mazumder
PY - 2026
DA - 2026/08/05
JO - Advanced Science
DO - 10.1002/advs.76944
UR - https://doi.org/10.1002/advs.76944
AB - Epitaxial all‐nitride Josephson junctions are promising components for high coherence superconducting qubits, yet nanoscale defects often limit their performance. The key to mitigating these defects lies in understanding the atomic‐scale relationship between polymorph selection, defect chemistry, and device performance. Here, we investigate structural and chemical defects in epitaxially grown 𝛿‐NbN/AlN/𝛿‐NbN, 𝛾‐Nb4N3/AlN/𝛾‐Nb4N3, β‐Nb2N/AlN/β‐Nb2N heterostructures on c‐plane sapphire using molecular beam epitaxy. Advanced microscopy integrated with density functional theory shows varying impurity distribution across different polymorphs. The chemical distribution reveals that δ‐NbN electrodes contain significant oxygen, whereas in β‐Nb2N/AlN/β‐Nb2N heterostructures oxygen preferentially segregates to the AlN barrier. DFT calculations indicate that these differences arise from phase‐dependent oxygen energetics and diffusion kinetics, with oxygen remaining kinetically trapped in δ‐NbN while exhibiting greater mobility in β‐Nb2N. These structural and chemical differences are consistent with the distinct transport behavior observed in the two junction architectures and provide mechanistic insight into the role of defect chemistry in epitaxial nitride Josephson junctions. The observed impurity distribution may influence superconducting properties and contribute to the formation of two‐level systems, a major source of loss and decoherence in superconducting quantum circuits.
SN - 2198-3844
ER -