GaN/NbN epitaxial semiconductor/superconductor heterostructures

• Published in: Nature (London) Vol. 555; no. 7695; pp. 183 - 189
• Main Authors: Yan, Rusen, Khalsa, Guru, Vishwanath, Suresh, Han, Yimo, Wright, John, Rouvimov, Sergei, Katzer, D. Scott, Nepal, Neeraj, Downey, Brian P., Muller, David A., Xing, Huili G., Meyer, David J., Jena, Debdeep
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 08.03.2018; Nature Publishing Group
• Subjects: 639/301/119/1003; 639/301/357/995; 639/925/927/1007; 639/925/927/1064; Aluminum; Aluminum gallium nitrides; Crystal structure; Crystallinity; Electron gas; Energy gap; Epitaxial growth; Epitaxy; Gallium; Gallium nitrides; Heterostructures; Humanities and Social Sciences; Molecular beam epitaxy; multidisciplinary; Niobium; Niobium nitride; Observations; Oscillators; Phase transitions; Photonic band gaps; Photonics; Piezoelectricity; Properties; Quantum wells; Radio frequency; Receivers & amplifiers; Science; Semiconductors; Semiconductors (Materials); Silicon; Silicon carbide; Substrates; Superconductors; Temperature; Transistors
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature25768

Epitaxy is a process by which a thin layer of one crystal is deposited in an ordered fashion onto a substrate crystal. The direct epitaxial growth of semiconductor heterostructures on top of crystalline superconductors has proved challenging. Here, however, we report the successful use of molecular beam epitaxy to grow and integrate niobium nitride (NbN)-based superconductors with the wide-bandgap family of semiconductors—silicon carbide, gallium nitride (GaN) and aluminium gallium nitride (AlGaN). We apply molecular beam epitaxy to grow an AlGaN/GaN quantum-well heterostructure directly on top of an ultrathin crystalline NbN superconductor. The resulting high-mobility, two-dimensional electron gas in the semiconductor exhibits quantum oscillations, and thus enables a semiconductor transistor—an electronic gain element—to be grown and fabricated directly on a crystalline superconductor. Using the epitaxial superconductor as the source load of the transistor, we observe in the transistor output characteristics a negative differential resistance—a feature often used in amplifiers and oscillators. Our demonstration of the direct epitaxial growth of high-quality semiconductor heterostructures and devices on crystalline nitride superconductors opens up the possibility of combining the macroscopic quantum effects of superconductors with the electronic, photonic and piezoelectric properties of the group III/nitride semiconductor family. Group III/nitride semiconductors have been grown epitaxially on the superconductor niobium nitride, allowing the superconductor’s macroscopic quantum effects to be combined with the semiconductors’ electronic, photonic and piezoelectric properties. Mix and match The perfect epitaxial growth of one crystalline semiconductor on another is a fundamental feature of many high-performance electronic and optoelectronic devices. Rusen Yan and colleagues demonstrate that a similar level of epitaxial integration can be achieved between the group III nitride semiconductors and the superconducting nitride metal NbN x . This ability to grow highly ordered, high-quality semiconducting structures directly on a crystalline superconductor provides a route for exploring a host of new device possibilities that combine the properties of the two subsystems.