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

摘要

A normally-off semiconductor element that has low on-resistance is provided. An epitaxial substrate for said semiconductor element comprises: a base substrate; a channel layer comprising a first group-III nitride that contains at least aluminum and gallium and has the composition In x1 Al y1 Ga z1 N (x1 + y1 + z1 = 1); and a barrier layer comprising a second group-III nitride that contains at least indium and aluminum and has the composition In x2 Al y2 Ga z2 N (x2 + y2 + z2 = 1). The composition of the first group-III nitride falls within the range delineated by x1 = 0 and 0 = y1 = 0.3. On a ternary phase diagram with InN, AlN, and GaN as the vertices, the composition of the second group-III nitride lies within an area bounded by straight lines represented by a plurality of formulas determined in accordance with the composition of the first group-III nitride. The barrier layer is at most 3 nm thick. The epitaxial substrate is further provided with a low-crystallinity insulating layer on top of the barrier layer, said low-crystallinity insulating layer comprising silicon nitride and being at most 3 nm thick.