Researchers have grown a nanoscale layer of a superconducting material which can integrate quantum qubits with existing microelectronics.
Scientists from Japan have discovered how a superconducting material, niobium nitride, can be added as a flat, crystalline layer to a nitride-semiconductor substrate. This technique could make it simple to manufacture quantum qubits that can be used with conventional computer devices. Discovering a technique to integrate quantum and conventional logic units on a single chip, or even adding quantum capabilities to existing fabrication lines, might greatly hasten the adoption of these new systems.
A group of scientists from The University of Tokyo’s Institute of Industrial Science demonstrated how thin films of niobium nitride (NbNx) can grow directly on top of an aluminum nitride (AlN) layer. Niobium nitride can become superconducting at temperatures colder than 16 degrees Celsius above absolute zero. Because of this, it can be utilized to create a superconducting qubit when arranged in a structure called a Josephson junction.
“We found that because of the small lattice mismatch between aluminum nitride and niobium nitride, a highly crystalline layer could grow at the interface, the structural similarity between the two materials facilitates the integration of superconductors into semiconductor optoelectronic devices,” said first and corresponding author Atsushi Kobayashi.
The scientists investigated the impact of temperature on the crystal structures and electrical properties of NbNx thin films grown on AlN template substrates. They showed that the spacing of atoms in the two materials was compatible enough to produce flat layers.
The crystalline nature of the NbNx was characterized with X-ray diffraction, and the surface topology was captured using atomic force microscopy. The team also showed how the arrangement of atoms, nitrogen content, and electrical conductivity all depended on the growth conditions, especially the temperature.
This interface between the AlN substrate, which has a wide bandgap, and NbNx is essential for future quantum devices, such as Josephson junctions. Superconducting layers that are only a few nanometers thick and have high crystallinity can be used as detectors of single photons or electrons.
Reference: “Crystal-Phase Controlled Epitaxial Growth of NbNx Superconductors on Wide-Bandgap AlN Semiconductors” by Atsushi Kobayashi, Shunya Kihira, Takahito Takeda, Masaki Kobayashi, Takayuki Harada, Kohei Ueno and Hiroshi Fujioka, 21 September 2022, Advanced Materials Interfaces.