| abstract |
Provided is an epitaxial substrate for a field effect transistor. In the epitaxial substrate, a nitride-based group 3-5 semiconductor epitaxial crystal, containing Ga, is arranged between a base substrate and an operation layer, and the nitride-based group 3-5 semiconductor epitaxial crystal contains the following layers (i, ii, iii); (i) a first buffer layer which contains Ga or Al and a high resistance crystal layer added with a compensating impurity element of the same period as Ga on the periodic table and has a small atomic number, (ii) a second buffer layer, which is stacked on the operation layer side of the first buffer layer and contains Ga or Al, and (iii) a high-purity epitaxial crystal layer, which is arranged between the high resistance crystal layer and the operation layer, and has no additive or contains an acceptor impurity of such a small quantity as to maintain the depletion state. |