Epitaxial substrate for electronic device, in which current flows in lateral direction and method of producing the same

An epitaxial substrate for electronic devices, comprising:

• a high-resistance Si-single crystal substrate;
• a barrier layer against impurity diffusion formed on one surface of the high-resistance Si-single crystal substrate;
• a buffer as an insulating layer formed on the other surface of the high-resistance Si-single crystal substrate;
• and
• a main laminate formed by epitaxially growing a plurality of III-nitride layers on the buffer,
• wherein the barrier layer against impurity diffusion prevents III elements from diffusing into the high-resistance Si-single crystal substrate from the one surface of the high-resistance Si-single crystal substrate during epitaxially growing the plurality of III group nitride layers, and
• wherein a lateral direction is a current flow direction, and
• in a region of the high-resistance Si-single crystal substrate from the one surface to a depth of 1 μm, III-element concentration is 1×1016 atoms/cm3 or less.