We control the crystal phase, polarity, local structure, and heterointerfaces of nitride materials to create new materials and electronic devices that integrate semiconducting, ferroelectric, and superconducting functionalities. A key advantage of the sputtering technique is that it forms high-quality epitaxial films at relatively low growth temperatures.

Integration of Superconductors and Semiconductors

Nitride superconductors such as NbN are promising materials for qubits in quantum computers and for single-photon detectors. We are developing techniques to control the crystal phase of NbN while forming high-quality epitaxial interfaces with nitride semiconductors such as AlN and GaN. Because a Josephson junction can be formed by sandwiching a thin nitride semiconductor layer between superconducting layers, we aim to realize novel devices that integrate superconducting and semiconducting functionalities within a single nitride heterostructure.

Development of Polar and Ferroelectric Nitrides

In AlN-based nitrides, the polarization, piezoelectricity, and ferroelectricity can be widely tuned through the choice of alloying elements and the atomic arrangement. In addition to ferroelectric ScAlN, we grow new nitride thin films such as NbAlN, BAlN, and ScAlGaN, and investigate how their crystal structure, local atomic arrangement, and polarity govern their physical properties.

Polarization-Engineered Nitride Heterostructures and Electronic Devices

Stacking polar nitrides on GaN induces a high density of electrons at the interface. We employ ScAlN and NbAlN as barrier layers in GaN-based heterostructures and work on controlling lattice matching, interface structure, and the two-dimensional electron gas. Through this research, we aim to realize high-power and high-frequency transistors, as well as electronic devices with memory functionality based on polarization switching.

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