US Patent 8384089 Nitride semiconductor device and method of manufacturing the same

A nitride semiconductor device including: a substrate; a nitride semiconductor layer formed on the substrate and having a heterojunction interface; and a recess portion formed on the nitride semiconductor layer, wherein the nitride semiconductor layer includes: a carrier transit layer, which has a composition represented by the formula: Alx1Inx2Ga1−x1−x2N, (0≦x1≦1, 0≦x2≦1, 0≦(x1+x2)≦1); and a carrier supply layer including: a first layer formed on the carrier transit layer, said first layer having a composition represented by the formula: AlyGa1−yN, (0<y≦1, x1<y); a second layer formed on the first layer, said second layer containing GaN; and a third layer formed on the second layer, said third layer having a composition represented by the formula: AlzGa1−zN, (0<z≦1, x1<z), and wherein the recess portion is formed to penetrate the third layer and expose a surface of the second layer at a bottom portion of the recess portion.