Epitaxial substrate for electronic device and method of producing the same

A method of producing an epitaxial substrate for an electronic device, the epitaxial substrate comprising:

• a conductive SiC single crystal substrate,
• a buffer as an insulating layer on the SiC single crystal substrate, and
• a main laminate formed by epitaxially growing a plurality of Group III nitride layers on the buffer,
• wherein a lateral direction is a current flow direction,
• the buffer includes at least an initial growth layer in contact with the SiC single crystal substrate and a superlattice laminate having a superlattice multi-layer structure on the initial growth layer,
• the initial growth layer is made of a Ba1Alb1Gac1Ind1N (0≦a1≦1, 0<b1≦1, 0≦c1≦1, 0≦d11, a1+b1+c1+d1=1) material,
• the superlattice laminate is configured by alternately stacking a first layer made of a B2Alb2Gac2Ind2N (0≦a2≦1, 0≦b2≦1, 0≦c2≦1, 0≦d2≦1, a1+b2+c2+d2=1) material and a second layer made of a Ba3Alb3Gac3Ind3N (0≦a3≦1, 0≦b3≦1, 0≦c3≦1, 0≦d3≦1, a3+b3+c3+d3=1) material having a different band gap from the first layer, and
• at least one of the superlattice laminate and a portion of the main laminate on the buffer side has a C concentration of 1×1018/cm3 or more.