Surface morphology and thickness dependence of the properties of MgB ₂ thin films by hybrid physical-chemical vapor deposition

The influence of growth parameters in hybrid physical-chemical vapor deposition (HPCVD) on surface morphologies of MgB₂ thin films, and the dependence of their properties on film thickness are systematically studied. As the HPCVD MgB₂ films grow in the Volmer-Weber mode, where islands coalesce into continuous films, the grain size has an important influence on the film morphology. We found that films deposited with higher growth rates have larger grains, and a larger grain size appears to correspond to a larger film roughness. Under optimized deposition conditions, the surface root mean square (RMS) roughness is 1.2nm over a 1νm × 1νm area for a 100nm thick film. The surface morphology does not directly affect the structural and superconducting properties of the MgB₂ films. The results of ultrathin MgB₂ films, as thin as 10nm, with excellent superconducting properties are also presented in this paper.