Abstract: A nitride compound semiconductor has a substrate and a nitride compound semiconductor stack on the substrate. The nitride compound semiconductor stack includes a multilayer buffer layer, a channel layer on this multilayer buffer layer, and an electron supply layer on this channel layer. A recess extends from the surface of the electron supply layer through the channel layer and the multilayer buffer layer. A heat dissipation layer in this recess is contiguous to the multilayer buffer layer and the channel layer and has a higher thermal conductivity than the multilayer buffer layer.

Abstract: A method for producing a nitride semiconductor stacked body includes: a first nitride semiconductor layer forming step of forming a first nitride semiconductor layer above a substrate within a reaction furnace; a second nitride semiconductor layer forming step of forming a second nitride semiconductor layer above the first nitride semiconductor layer; and a third nitride semiconductor layer forming step of forming a third nitride semiconductor layer on the upper surface of the second nitride semiconductor layer, the third nitride semiconductor layer having a band gap larger than the band gap of the second nitride semiconductor layer. No interval is provided between the second nitride semiconductor layer forming step and the third nitride semiconductor layer forming step, and the third nitride semiconductor layer forming step is performed continuously after the second nitride semiconductor layer forming step.

Abstract: In a nitride semiconductor including a Si substrate and a nitride semiconductor stacked body disposed on the Si substrate, the half value width of an X-ray diffraction rocking curve of the Si substrate is less than 160 arcsec.

Abstract: A nitride compound semiconductor has a substrate and a nitride compound semiconductor stack on the substrate. The nitride compound semiconductor stack includes a multilayer buffer layer, a channel layer on this multilayer buffer layer, and an electron supply layer on this channel layer. A recess extends from the surface of the electron supply layer through the channel layer and the multilayer buffer layer. A heat dissipation layer in this recess is contiguous to the multilayer buffer layer and the channel layer and has a higher thermal conductivity than the multilayer buffer layer.

Abstract: A nitride semiconductor layered body includes a Si substrate having a surface, as the principal surface, inclined at an off-angle of 0 degrees or more and 4.0 degrees or less with respect to a plane and a nitride semiconductor layer disposed on the Si substrate.