Ultra-thin Epitaxial MgB2 on SiC: Substrate Surface Polarity Dependent Properties

TL;DR

This study demonstrates the fabrication of ultrathin MgB2 superconducting films on SiC substrates, revealing that surface termination significantly affects film quality and superconducting properties, with the C-terminated surface being preferable.

Contribution

It provides new insights into how substrate surface polarity influences MgB2 film growth and properties, highlighting the importance of interface chemistry and structure.

Findings

MgB2 films as thin as 4 nm with Tc above 33K

C-terminated SiC surface yields higher quality MgB2 films

Interfacial oxide layers affect film morphology and superconductivity

Abstract

High quality, ultrathin, superconducting films are required for advanced devices such as hot-electron bolometers, superconducting nanowire single photon detectors, and quantum applications. Using Hybrid Physical-Chemical Vapor Deposition (HPCVD), we show that MgB2 films as thin as 4 nm can be fabricated on the carbon terminated 6H-SiC (0001) surface with a superconducting transition temperature above 33K and a rms roughness of 0.7 nm. Remarkably, the film quality is a function of the SiC surface termination, with the C-terminated surface preferred to the Si-terminated surface. To understand the MgB2 thin film/ SiC substrate interactions giving rise to this difference, we characterized the interfacial structures using Rutherford backscattering spectroscopy/channeling, electron energy loss spectroscopy, and x-ray photoemission spectroscopy. The MgB2/SiC interface structure is complex and different for the two terminations. Both terminations incorporate substantial unintentional oxide layers influencing MgB2 growth and morphology, but with different extent, intermixing and interface chemistry. In this paper, we report measurements of transport, resistivity, and critical superconducting temperature of MgB2/SiC that are different for the two terminations, and link interfacial structure variations to observed differences. The result shows that the C face of SiC is a preferred substrate for the deposition of ultrathin superconducting MgB2 films.