Properties of MgB2 Ultrathin Films Fabricated on MgO (111) Substrate by Hybrid Physical-Chemical Vapor Deposition

We fabricate MgB2 ultrathin films via the hybrid physical-chemical vapor deposition (HPCVD) technique. With the proper background pressure and B2H6 flow rate, we fabricate a series of ultrathin films ranging from 10 to 40 nm. These films grow on the MgO (111) substrate and are all c-axis epitaxial. The ultrathin films show good connectivity, very high T-c(0) approximate to 35-38 K, and very low residual resistivity rho(42 K) approximate to 1.8-20.3 mu Omega . cm. With the increase in the film thickness, the critical transition temperature increases, and the residual resistivity decreases. In addition, the 10-, 20-, and 40-nm films show extremely high critical current density, i.e., J(c) approximate to 2.0 x 10(7), 2.3 x 10(7), and 2.8 x 10(7) A/cm(2) at 5 K, respectively, which indicate that the films fabricated by HPCVD are well qualified for device applications.