Hybrid Physical - Chemical Vapor Deposition of Ultrathin MgB2 Films on MgO Substrate With High TC and JC

MgB₂ has been recognized as a candidate material for fabricating superconducting nanowire single photon detectors with the expectation of having an operating temperature of the detector at 10-20 K. Preparation of ultrathin MgB₂ films with high superconducting transition temperature T_C is the first crucial step to achieve this goal. Here we present the hybrid physical-chemical vapor deposition of MgB₂ superconducting films with thicknesses around 10 nm. The films are epitaxially grown on (111) MgO substrates. The T_C of the films, including for a 6-nm-thick film, is found to be above 34 K, close to the bulk value of MgB₂ (39 K). The normal-state resistivity at 42 K of a 10-nm-thick film is shown to be 3.1 μΩ cm, indicating that the film is relatively clean. The superconducting critical current density J_C of the films has also been measured on strip lines patterned in the films. The J_C of the 10-nm-thick film reaches 7.7 ×10⁷ A/cm² at 2 K, so far the highest value reported for MgB₂ films of the same thickness. The high T_C, low residual resistivity, and high J_C of the ultrathin MgB₂ films on MgO substrates suggest that these films have the potential in developing MgB₂-based superconducting nanowire single photon detectors or other related superconducting devices.