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

摘要

Disclosed is an epitaxial substrate that can realize the preparation of an HEMT element which has good two-dimensional electron gas properties and can realize normally-off operation. The epitaxial substrate comprises a channel layer formed of a first group III nitride represented by Inx1Aly1Gaz1N wherein x1 + y1 + z1 = 1 and which has a composition satisfying x1 = 0 and 0 = y1 = 0.3. The epitaxial substrate further comprises a barrier layer formed of a second group III nitride represented by Inx2Aly2Gaz2N wherein x2 + y2 + z2 = 1 and which has a composition that falls within an area surrounded by four straight lines determined dependent upon the composition of the first group III nitride (AlN molar fraction) on a ternary phase diagram in which InN, AlN, and GaN constitute vertices. The barrier layer has a thickness of not more than 5 nm.