Molecular Beam Epitaxy of Transition Metal Nitrides for Superconducting Device Applications

摘要

Epitaxial integration of superconductors with semiconductors is expected toenable new device architectures and to increase electronic circuit and systemfunctionality and performance in diverse fields, including sensing and quantumcomputing. Herein, radiofrequency plasma molecular-beam epitaxy is used toepitaxially grow 3–200 nm-thick metallic NbNx and TaNx thin films on hexagonalSiC substrates. Single-phase cubic δ-NbN and hexagonal TaNx films are obtainedwhen the starting substrate temperature is ≈800 and 900 ℃, respectively, andthe active N to Nb or Ta ratio is ≈2.5–3. The films are characterized using in-situreflection high-energy electron diffraction and ex-situ atomic force microscopy,contactless sheet resistance, X-ray diffraction, X-ray photoelectron spectroscopy,secondary ion-mass spectrometry, Rutherford backscattering spectrometry,cross-sectional transmission electron microscopy, and low-temperature electricalmeasurements. Smooth, epitaxial, low-resistivity films of cubic δ-NbN andhexagonal TaNx on SiC are demonstrated for films at least ≈50 nm-thick, andtheir superconducting properties are reported. Epitaxy of AlN and GaN on δ-NbNis also demonstrated, as well as integration of an epitaxial NbNx superconductingelectrode layer under GaN high-electron mobility transistors. These early demonstrationsshow the promise of direct epitaxial integration of superconductingtransition metal nitrides with group Ⅲ-N semiconductors.