Surface morphology and thickness dependence of the properties of MgB2 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 1.2 nm over a 1 mu m x 1 mu m area for a 100 nm 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 10 nm, with excellent superconducting properties are also presented in this paper.