MgB2 thin films grown at different temperatures by hybrid physical-chemical vapor deposition

We have grown MgB₂ films at different substrate temperatures by hybrid physical-chemical vapor deposition. X-ray diffraction analysis shows epitaxial growth at all temperatures, as measured at the substrate surface, between 550-700°C. An optimal deposition temperature was found around 650°C, at which the rocking curve is the narrowest, the residual resistivity is the lowest, and T_c is the highest. For the films deposited at lower temperatures, the rocking curve broadens, indicating a decreasing quality of crystallinity. The residual resistivity increases but the superconducting transition temperature remains nearly constant around 40 K when the deposition temperature is decreased to 550°C. The deposition of epitaxial films with excellent superconducting properties at low substrate temperatures is important for device and circuit processing utilizing MgB₂.