Epitaxial Ultrathin MgB₂ Films on C-Terminated 6H-SiC(${\text{000}}\bar{{\text{1}}}$) Substrates Grown by HPCVD

Ultrathin superconducting MgB ₂ films are desirable for device applications and for exploration of new quantum phenomena in reduced dimensions. We have reported recently that smooth ultrathin MgB ₂ films can be grown on carbon-terminated SiC substrates using Hybrid Physical-Chemical Vapor Deposition (HPCVD). In this work, we present a thickness dependence study of HPCVD-grown ultrathin MgB ₂ films on C-terminated SiC with a focus on the thinnest superconducting films. The thickness of a nominally 2 nm thick MgB ₂ film, controlled by deposition time based on thickness calibration data from thicker films, was confirmed by cross-sectional imaging via scanning transmission electron microscopy. We obtained a superconducting transition temperature T _c = 27.2 K, a self-field critical current density J _c (3K, 0T) = 2 × 10 ⁷ A/cm ² , and a normal-state sheet resistance near the transition R_s = 44.5 Ω/sq in a 2 nm thick MgB ₂ film while its root-mean-square roughness was 0.62 nm. These characteristics make the HPCVD-grown ultrathin MgB ₂ films highly attractive for superconducting electronic applications.