Substrate net-doping concentration (N-d) was found to strongly affect on the quality performance of grown epitaxial layer. Schottky Barrier Diode (SBD) with epitaxy layer grown on the substrate with relatively low doping concentration (N-d=2x10(18) cm(-3)) exhibited the highest breakdown voltage (V-b) as well as critical field (E-c =2.0 MV/cm). Where as thus on the higher dopant-density substrates (N-d 1x10(19) cm(-3)) performed E-c of about 80% or less to that of the low doping concentration. High N-d was confirmed by XRD to cause the broadening of Rocking curves and slight expanding in lattice constant in SiC substrates. Moreover, high N-d substrate was detected by ICTS to cause the formation of high defect density in the grown epitaxy layer. Based on these results, insertion of buffer layer was proposed for limitation of the defect formation in the grown SiC layer.