MgB2 superconducting films with a thickness of 10 nm to 8 μ have been prepared on SiC substrates by hybrid physical-chemical vapor deposition (HPCVD). The study on Tc and Jc shows that as the film grows thicker, Tc increases and then keeps stable, which Jc increases at first, and then drops dramatically. We get the maximum Tc at 41.4 K and Jc at 2.3× 108 A·cm-2. This also shows that we can use the method of HPCVD to prepare high-quality of clean MgB2 film. And its thickness can be from 10nm ultrathin films and 100 nm thin films up to 8 μm thick film. It is the first time so far as we know that Tc and Jc are studied in this range of thickness. This will lead to a complete and systematical understanding of the superconducting MgB2 films. And it is also important and practical to choose the thickness when preparing MgB2 films.
We fabricate MgB2 ultra-thin films via hybrid physics-chemical vapor deposition technique (HPCVD). Under the same background pressure, the same H2 flow rate and the same deposition time, by changing the B2H6 flow rate, we fabricate a series of ultra-thin films with thickness values ranging from 10 nm to 40 nm. These films grow on MgO(111) substrate, and are all c-axis epitaxial. These films show the good connectivity, a very high Tc(0) ≈ 35-38 K and a very low residual resistivity ρ(42 K) ≈ 1.8-20.3 μΩ·cm-1. As the thickness increases, critical transition temperature also increases and the residual resistivity decreases. The 20 nm film also shows an extremely high critical current density Jc (0 T, 5 K) ≈ 2.3×107 A/cm2, which indicates that the films fabricated by HPCVD are well qualified for device applications.
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