Semiconductor element and device
A semiconductor element includes a first semiconductor layer, a second semiconductor layer, a third semiconductor layer, a fourth semiconductor layer, a first intermediate layer, a second intermediate layer, a source electrode, a drain electrode, and a gate electrode. The band gap of the second semiconductor layer is larger than the band gaps of the first semiconductor layer and the third semiconductor layer. The band gaps of the first intermediate layer and the second intermediate layer that sandwich the second semiconductor layer are larger than the band gap of the second semiconductor layer.
1 . A semiconductor element comprising:
a first semiconductor layer;
a second semiconductor layer located above the first semiconductor layer;
a third semiconductor layer located above the second semiconductor layer;
a fourth semiconductor layer located above the third semiconductor layer;
a first intermediate layer located between the first semiconductor layer and the second semiconductor layer;
a second intermediate layer located between the second semiconductor layer and the third semiconductor layer;
a source electrode and a drain electrode located on the second semiconductor layer or the third semiconductor layer;
a gate electrode located on the fourth semiconductor layer;
a gate electrode contact region where the gate electrode is in contact with the fourth semiconductor layer;
a source electrode contact region where the source electrode is in contact with the second semiconductor layer or the third semiconductor layer; and
a drain electrode contact region where the drain electrode is in contact with the second semiconductor layer or the third semiconductor layer, wherein
the first semiconductor layer, the second semiconductor layer, the third semiconductor layer, and the fourth semiconductor layer are group-III nitride semiconductor layers,
the first intermediate layer and the second intermediate layer are group-III nitride layers,
the second semiconductor layer has a band gap larger than those of the first semiconductor layer and the third semiconductor layer,
the first intermediate layer and the second intermediate layer have respective band gaps larger than that of the second semiconductor layer,
the first semiconductor layer, the second semiconductor layer, and the third semiconductor layer are undoped semiconductor layers,
the fourth semiconductor layer is a p-type semiconductor layer, and
a region obtained by projecting the gate electrode contact region on the second semiconductor layer surrounds a circumference of a region obtained by projecting the source electrode contact region or the drain electrode contact region on the second semiconductor layer.
2 . The semiconductor element according to claim 1 , further comprising a polarization super junction region where the third semiconductor layer is formed and the fourth semiconductor layer is not formed and which is located between the gate electrode contact region and the drain electrode contact region.
3 . The semiconductor element according to claim 2 , wherein
the first semiconductor layer has a first two-dimensional electron gas on a side toward the first intermediate layer,
the third semiconductor layer has a first two-dimensional hole gas on a side toward the second intermediate layer, and
the second semiconductor layer has a second two-dimensional hole gas on a side toward the first intermediate layer and a second two-dimensional electron gas on a side toward the second intermediate layer.
4 . The semiconductor element according to claim 3 , wherein a sheet electron concentration of first two-dimensional electron gas is larger than a sheet hole concentration of second two-dimensional hole gas.
5 . The semiconductor element according to claim 3 , wherein an energy level of a conduction band lower edge of the second semiconductor layer increases toward the first intermediate layer.
6 . The semiconductor element according to claim 1 , wherein
the first intermediate layer has a thickness of 0.2 nm to 10 nm, and
the second intermediate layer has a thickness of 0.2 nm to 10 nm.
7 . The semiconductor element according to claim 1 , wherein the first intermediate layer and the second intermediate layer contain Al.
8 . The semiconductor element according to claim 7 , wherein each of the first intermediate layer and the second intermediate layer has an Al composition ratio of 0.5 or greater.
9 . The semiconductor element according to claim 1 , wherein
a sheet carrier concentration at an interface between the first intermediate layer and the second semiconductor layer is 2×10 13 cm −2 or less, and
a sheet carrier concentration at an interface between the second intermediate layer and the second semiconductor layer is 2×10 13 cm −2 or less.
10 . The semiconductor element according to claim 1 , wherein
the first semiconductor layer has a first two-dimensional electron gas on a side toward the first intermediate layer,
the third semiconductor layer has a first two-dimensional hole gas on a side toward the second intermediate layer, and
the second semiconductor layer has a second two-dimensional hole gas on a side toward the first intermediate layer and a second two-dimensional electron gas on a side toward the second intermediate layer.
11 . The semiconductor element according to claim 10 , wherein a sheet electron concentration of first two-dimensional electron gas is larger than a sheet hole concentration of second two-dimensional hole gas.
12 . The semiconductor element according to claim 10 , wherein an energy level of a conduction band lower edge of the second semiconductor layer increases toward the first intermediate layer.