Epitaxial Integration of Superconducting Transition-Metal Nitrides with Cubic Gallium Nitride

The thermodynamically stable wurtzite phase of GaN is ubiquitous in the optoelectronics industry, but it also has a metastable zinc blende allotrope. Cubic-GaN (c-GaN) is still a direct bandgap semiconductor with a bandgap of 3.2 eV and can be doped both n-type and p-type, rare for cubic materials with such bandgaps. Unlike the wurtzite phase, c-GaN is centrosymmetric and therefore does not have issues with polarization. Another potential advantage of the higher symmetry is the simplified interfacing with the other cubic materials. The rocksalt structured transition metal nitrides are of interest for applications requiring high chemical and thermal stability, high hardness, superconductivity, or plasmonics.

This work will discuss the synthesis of epitaxial c-GaN on 3C-SiC substrates and the integration with known superconducting nitrides via molecular beam epitaxy. The hexagonal-free nature of the c-GaN and epitaxial relationship with the transition metal nitrides, are confirmed via in-situ reflection high energy electron diffraction, ex-situ X-ray diffraction, photoluminescence, and transition electron microscopy. Electrical transport and optical properties of epitaxial transition metal nitrides on c-GaN(001) are compared to growth directly on 3C-SiC(001) and c-plane wurtzite GaN substrates. The growth windows for GaN and some metal nitrides are close, which allows for deposition of metal-dielectric multilayers. Epitaxial synthesis of a cubic wide-bandgap and superconducting metallic nitrides opens a new world of possibilities in band engineering, metamaterials, and quantum devices. This will create an avenue for new hierarchical matter by combining materials with dissimilar properties with atomic layer precision.