EPITAXIAL SUBSTRATE AND METHOD FOR PRODUCING EPITAXIAL SUBSTRATE

摘要

Disclosed is a crack-free epitaxial substrate which uses a silicon substrate as a base substrate and has excellent withstand voltage. Specifically disclosed is an epitaxial substrate which is obtained by forming a group of group III nitride layers on a (111) single crystal silicon base substrate such that the (0001) crystal plane is generally parallel to the substrate surface. The epitaxial substrate comprises: a buffer layer which comprises a plurality of composition modulation layers wherein first composition layers that are formed from AlN and second composition layers that are formed from AlxGa1-xN (wherein 0 = x < 1) are alternately laminated; and a crystal layer that is formed on the buffer layer. When the respective numbers of the first composition layers and the second composition layers laminated are represented by n and the value of x in the i-th second composition layer from the base substrate is represented by x(i), x(1) = x(2) = ··· = x(n-1) = x(n) and x(1) > x(n) are satisfied. The second composition layers are coherent to the first composition layers.