COMPOUND SEMICONDUCTOR SUBSTRATE

摘要

PROBLEM TO BE SOLVED: To provide a compound semiconductor substrate which can satisfy both of high performance and reliability of a semiconductor element while suppressing a film thickness of an entire compound semiconductor layer.SOLUTION: A compound semiconductor substrate comprises: a silicon single crystal substrate 12; a first semiconductor layer 16 having a carbon concentration of not less than 1×10/cmand not more than 1×10/cm; a barrier layer 18 which has a carbon concentration equal to or less than 5×10/cmand has bandgap energy larger than that of the first semiconductor layer 16; a second semiconductor layer 20 which has a carbon concentration equal to or less than 5×10/cmand has bandgap energy smaller than that of the barrier layer; and a third semiconductor layer 22 having bandgap energy larger than that of the second semiconductor layer. The first semiconductor layer and the barrier layer are lattice matched to each other at a first boundary surface. The barrier layer and the second semiconductor layer are lattice matched to each other at a second boundary surface. Bandgap energy inside the barrier layer is larger than bandgap energy of the barrier layer at the first boundary surface and larger than bandgap energy of the barrier layer at the second boundary surface.