EPITAXIAL SUBSTRATE FOR SEMICONDUCTOR ELEMENT, SEMICONDUCTOR ELEMENT, AND METHOD FOR PRODUCING EPITAXIAL SUBSTRATE FOR SEMICONDUCTOR ELEMENT

摘要

Disclosed is an epitaxial substrate which uses a silicon substrate as a base substrate and is capable of providing an HEMT element that has high 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 Si substrate such that the (0001) crystal plane is generally parallel to the substrate surface. The epitaxial substrate is provided with: a first group III nitride layer that is a layer containing multiple defects, said layer being formed from AlN and configured of columnar or granular crystals and/or domains; a second group III nitride layer that has a three dimensionally recessed and projected surface at the interface with the first group III nitride layer; and a third group III nitride layer that is epitaxially grown on the second group III nitride layer and is formed as a composition gradient layer in which the presence ratio of Al decreases toward a fourth group III nitride.