Semiconductor device
A semiconductor device includes: an electron transit layer constituted of GaN; an electron supply layer constituted of In x1 Al y1 Ga 1−x1−y1 N (0≦x1<1, 0≦y1<1, 0<1−x1−y1<1) and provided on the electron transit layer; a source electrode and a drain electrode that are provided on the electron supply layer and located apart from each other; a threshold voltage adjustment layer constituted of In x2 Al y2 Ga 1−x2−y2 N (0≦x2<1, 0≦y2<1, 0<1−x2−y2≦1) of a p-type and provided on a part of the electron supply layer located between the source electrode and the drain electrode; and a gate electrode provided on the threshold voltage adjustment layer. A high resistance layer is respectively interposed both between the gate electrode and the threshold voltage adjustment layer, and between the threshold voltage adjustment layer and the electron supply layer.
1. A semiconductor device comprising:
an electron transit layer constituted of gallium nitride;
an electron supply layer constituted of In x1 Al y1 Ga 1−x1−y1 N (0≦x1<1, 0≦y1<1, 0<1−x1−y1<1) and provided on the electron transit layer;
a source electrode provided on the electron supply layer;
a drain electrode provided on the electron supply layer and is apart from the source electrode;
a threshold voltage adjustment layer constituted of In x2 Al y2 Ga 1−x2−y2 N (0≦x2<1, 0≦y2<1, 0<1−x2−y2≦1) of a p-type and provided on a part of the electron supply layer between the source electrode and the drain electrode; and
a gate electrode provided on the threshold voltage adjustment layer,
wherein
the electron supply layer contains aluminum, and a composition ratio of aluminum in the electron supply layer increases continuously from a side of the electron supply layer adjacent the electron transit layer toward a side of the electron supply layer adjacent the threshold voltage adjustment layer, and
a high resistance layer is interposed between the gate electrode and the threshold voltage adjustment layer.
2. The semiconductor device according to claim 1 , wherein
the gate electrode contains tungsten,
a crystal defect layer which was generated in sputtering tungsten or metal containing tungsten onto the threshold voltage adjustment layer is exposed on an interface between the threshold voltage adjustment layer and the gate electrode, and
the crystal defect layer is the high resistance layer.
3. The semiconductor device according to claim 1 , wherein
the threshold voltage adjustment layer constituted of gallium nitride of the p-type,
one of p-type gallium nitride containing impurities in a lower concentration than the p-type gallium nitride of the threshold voltage adjustment layer, i-type gallium nitride, n-type gallium nitride, an insulating layer selected from SiO 2 , SiN, MO, and GaO, or a nitride semiconductor layer which forms heterojunction with the threshold voltage adjustment layer is interposed between the gate electrode and the threshold voltage adjustment layer.