Properties of MgB2 ultra-thin films grown by hybrid physical-chemical vapor deposition

We fabricate MgB 2 ultra-thin films via hybrid physical-chemical vapor deposition technique. Under the same background pressure, the same H 2 flow rate, by changing B 2 H 6 flow rate and deposition time, we fabricate a series of ultra-thin films with thickness ranging from 5 nm to 80 nm. These films grow on SiC substrate, and are all c -axis epitaxial. We study the Volmer-Weber mode in the film formation. As the thickness increases, critical transition temperature T c (0) also increases and the residual resistivity decreases. Especially, a very high T c (0) ≈ 32.8 K for the 7.5 nm film, and T c (0) ≈ 36.5 K, low residual resistivity ρ (42 K)≈ 17.7 μΩcm, and extremely high critical current density J c (0 T,4 K) ≈ 10 7 A/cm 2 , upper critical field H c2 (0) for 10 nm film are achieved. Moreover, by optimizing the H 2 flow rate, we obtain relatively smooth surface of the 10 nm epitaxial film, with a root-mean-square roughness of 0.731 nm, which makes them well qualified for device applications.