Patent ID: 7935984

Claim:
A compound semiconductor epitaxial substrate for a planar device, comprising: a channel layer in which electrons travel; and an epitaxial layer on each of a front side and a back side of the channel layer, wherein a total p-type carrier concentration A (/cm 2 ) per unit area in the epitaxial layer on the back side of the channel layer and a total p-type carrier concentration B (cm 2 ) per unit area in the epitaxial layer on the front side of the channel layer satisfy the following expression (1): 0< A/B≦ 3.5 (1) wherein A=(a concentration of all p-type carriers in an active state due to an acceptor impurity contained in the epitaxial layer on the back side of the channel layer)×(a total thickness of the epitaxial layer on the back side), and B=(a concentration of all p-type carriers in an active state due to an acceptor impurity contained in the epitaxial layer on the front side of the channel layer)×(a total thickness of the epitaxial layer on the front side).