Investigations of MgB2/MgO and MgB2/AlN heterostructures for Josephson devices

We report structural and transport proprieties of MgB₂/MgO and MgB₂/AlN multilayers for MgB₂ Josephson junctions. The MgB₂ layers were grown by hybrid physical chemical vapor deposition (HPCVD). The epitaxial MgB₂/MgO/MgB₂ trilayers were grown in situ in the HPCVD system. The AlN layers were grown at room temperature by pulsed laser deposition, and the MgB₂/AlN/MgB₂ trilayers were deposited ex situ with the deposition of the AlN layer between the depositions of the top and bottom MgB₂ layers. Although slightly less perfect than in films grown directly on sapphire and SiC substrates, excellent superconducting and transport properties were obtained in the MgB₂ layers in both heterostructures. The result addressed only the first of many issues about the adequacy of using MgO and AlN as the barrier materials for all-MgB₂ planar Josephson junctions, i.e. the ability to obtain good structural and superconducting properties in both electrode layers using the trilayer deposition process. It allows us to further investigate the conditions for better wetting and coverage of the insulator layers, as well as other critical issues in the fabrication of all-MgB₂ planar Josephson junctions.