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.