Semiconductor device
According to one embodiment, a semiconductor device includes a first crystal region, a second crystal region, a third crystal region, and a fourth crystal region. The first crystal region includes magnesium and Al x1 Ga 1-x1 N (0≤x1<1). The second crystal region includes Al x2 Ga 1-x2 N (0<x2≤1). The third crystal region is provided between the first crystal region and the second crystal region. The third crystal region includes oxygen and Al x3 Ga 1-x3 N (0≤x3≤1 and x3<x2). The fourth crystal region is provided between the third crystal region and the second crystal region. The fourth crystal region includes Al x4 Ga 1-x4 N (0≤x4<1 and x4<x2).
1. A semiconductor device, comprising:
a first crystal region including magnesium and Al x1 Ga 1-x1 N (0≤x1<1);
a second crystal region including Al x2 Ga 1-x2 N (0<x2≤1);
a third crystal region provided between the first crystal region and the second crystal region, the third crystal region including oxygen and Al x3 Ga 1-x3 N (0≤x3≤1 and x3<x2); and
a fourth crystal region provided between the third crystal region and the second crystal region, the fourth crystal region including Al x4 Ga 1-x4 N (0≤x4<1 and x4<x2).
2. The device according to claim 1 , wherein
a concentration of oxygen in the third crystal region is not less than 2×10 17 cm −3 and not more than 1×10 20 cm −3 .
3. The device according to claim 1 , wherein
the third crystal region includes silicon, and
the first crystal region does not include silicon, or a concentration of silicon in the first crystal region is less than a concentration of silicon in the third crystal region.
4. The device according to claim 3 , wherein
the fourth crystal region does not include silicon, or a concentration of silicon in the fourth crystal region is less than the concentration of silicon in the third crystal region.
5. The device according to claim 3 , wherein
the concentration of silicon in the third crystal region is not less than 1×10 17 cm −3 and not more than 5×10 19 cm −3 .
6. The device according to claim 1 , wherein
at least a portion of a crystal of the third crystal region is continuous with a crystal of the fourth crystal region.
7. The device according to claim 1 , wherein
at least a portion of a crystal of the third crystal region is continuous with a crystal of the first crystal region.
8. The device according to claim 1 , further comprising:
a fifth crystal region provided between the first crystal region and the third crystal region, the fifth crystal region including Al x5 Ga 1-x5 N (0<x5≤1, x1<x5, and x3<x5).
9. The device according to claim 8 , wherein
at least a portion of a crystal of the third crystal region is continuous with a crystal of the fifth crystal region.
10. The device according to claim 9 , wherein
the at least a portion of the crystal of the fifth crystal region is continuous with a crystal of the first crystal region.
11. The device according to claim 1 , wherein
a thickness of the third crystal region is not less than 2 nm and not more than 20 nm.
12. The device according to claim 1 , wherein
a thickness of the third crystal region is not less than 2 nm and not more than 10 nm.
13. The device according to claim 1 , wherein
the fourth crystal region does not include magnesium, or a fourth concentration of magnesium in the fourth crystal region is less than a first concentration of magnesium in the first crystal region.
14. The device according to claim 13 , wherein
the fourth concentration is not more than ⅕ of the first concentration.
15. The device according to claim 13 , wherein
a third concentration of magnesium in the third crystal region decreases along a first orientation,
the first orientation is from the first crystal region toward the fourth crystal region, and
a third change rate of a logarithm of the third concentration with respect to a change of a position along the first orientation is greater than a fourth change rate of a logarithm of the fourth concentration with respect to a change of a position along the first orientation.
16. The device according to claim 1 , wherein
a thickness of the fourth crystal region is not less than 10 nm and not more than 200 nm.
17. The device according to claim 1 , further comprising:
a substrate; and
a sixth crystal region including a nitride semiconductor including Al,
the sixth crystal region being between the substrate and the first crystal region.
18. The device according to claim 1 , further comprising:
a first electrode;
a second electrode; and
a third electrode,
a direction from a portion of the first crystal region toward the first electrode being along a first direction from the first crystal region toward the second crystal region,
a direction from an other portion of the first crystal region toward the second electrode being along the first direction,
a second direction from the first electrode toward the second electrode crossing the first direction,
a position in the second direction of the third electrode being between a position in the second direction of the first electrode and a position in the second direction of the second electrode.