Thickness dependence of the properties of epitaxial $MgB2$ thin films grown by hybrid physical-chemical vapor deposition

We have studied the effect of deposition rate and layer thickness on the properties of epitaxial $MgB2$ thin films grown by hybrid physical-chemical vapor deposition on 4H-SiC substrates. The $MgB2$ film deposition rate depends linearly on the concentration of $B2H6$ in the inlet gas mixture. We found that the superconducting and normal-state properties of the $MgB2$ films are determined by the film thickness, not by the deposition rate. When the film thickness was increased, the transition temperature $Tc$ increased and the residual resistivity $ρ0$ decreased. Above 3000 Å, a $Tc$ of 41.8 K, a $ρ0$ of 0.28 μΩ cm, and a residual resistance ratio $RRR$ of over 30 were obtained.