Nitride semiconductor device
A nitride semiconductor device includes a substrate, a nitride semiconductor laminate, and an ohmic electrode of TiAl-based material. The nitride semiconductor laminate has a first nitride semiconductor layer on the substrate, and a second nitride semiconductor layer forming a heterointerface with the first nitride semiconductor layer. The nitride semiconductor device has an oxygen concentration profile in a depth direction of the device across between the ohmic electrode and the nitride semiconductor laminate. The profile has a first oxygen concentration peak near an interface between the ohmic electrode and the nitride semiconductor laminate in a region, of the nitride semiconductor laminate, that is on a substrate side of the interface, and a second oxygen concentration peak having an oxygen concentration of 3×10 17 cm −3 -1.2×10 18 cm −3 in a position deeper than that of the first oxygen concentration peak.
1. A nitride semiconductor device comprising:
a substrate;
a nitride semiconductor laminate placed on the substrate and having a heterointerface;
an insulating film serving as a protection layer on the nitride semiconductor laminate;
an ohmic electrode comprising a TiAl-based material, a part of the ohmic electrode being placed in the nitride semiconductor laminate;
the nitride semiconductor laminate including a first nitride semiconductor layer placed on the substrate, and a second nitride semiconductor layer placed on the first nitride semiconductor layer and forming the heterointerface with the first nitride semiconductor layer; and
an oxygen concentration profile in a depth direction of the nitride semiconductor device across an interface between the ohmic electrode and the nitride semiconductor laminate, the oxygen concentration profile having:
a first oxygen concentration peak in a position in vicinity of the interface between the ohmic electrode and the nitride semiconductor laminate, the position of the first oxygen concentration peak being located in a region of the nitride semiconductor laminate that is on a substrate side of the interface between the ohmic electrode and the nitride semiconductor laminate, and
a second oxygen concentration peak in a position deeper than the position of the first oxygen concentration peak, the second oxygen concentration peak having an oxygen concentration that is 3×10 17 cm −3 or more but not more than 1.2×10 18 cm −3 ,
wherein the position of the second oxygen concentration peak is at a depth of 65 nm or more but not more than 110 nm from the interface between the ohmic electrode and the nitride semiconductor laminate.
2. The nitride semiconductor device according to claim 1 , wherein the nitride semiconductor laminate has a recess that penetrates the second nitride semiconductor layer and reaches a two dimensional electron gas layer in vicinity of the heterointerface, and the recess is filled with the part of the ohmic electrode.
3. The nitride semiconductor device according to claim 1 , wherein
the first nitride semiconductor layer includes a two dimensional electron gas layer near the heterointerface between the first nitride semiconductor layer and the second nitride semiconductor layer, and
the part of the ohmic electrode extends in the first nitride semiconductor to a position deeper than the two dimensional electron gas layer.
4. The nitride semiconductor device according to claim 2 , wherein the recess also penetrates the insulating film as well.
5. The nitride semiconductor device according to claim 1 , wherein the first and second oxygen concentration peaks are peaks obtained from SIMS measurement results.