Semiconductor device

1. A semiconductor device comprising:

a semiconductor layer;

a source electrode provided in the semiconductor layer;

a drain electrode provided in the semiconductor layer and spaced from the source electrode;

a first gate electrode provided between the source electrode and the drain electrode; and

a second gate electrode provided between the source electrode and the drain electrode, the second gate electrode having at least a part thereof located closer to the drain electrode than the first gate electrode,

the semiconductor layer including:

a first facing part that is a part facing the first gate electrode; and

a second facing part that is a part facing the second gate electrode,

wherein the first facing part does not conduct when a first gate voltage is 0 V or less, the first gate voltage being a potential difference between the source electrode and the first gate electrode,

wherein the second facing part does not conduct when a second gate voltage is 0 V or less, the second gate voltage being a potential difference between the second gate electrode and a part of the semiconductor layer located between the first facing part and the second facing part, and

wherein the first gate voltage at which the first facing part begins to conduct is larger than the second gate voltage at which the second facing part begins to conduct.

2. The semiconductor device according to claim 1 ,

wherein one or both of a part of the semiconductor layer between the first facing part and the first gate electrode and a part of the semiconductor layer between the second facing part and the second gate electrode are doped with fluoride ions.

3. The semiconductor device according to claim 1 ,

wherein at least one of the first gate electrode and the second gate electrode is P-type gate.

4. The semiconductor device according to claim 1 ,

wherein the semiconductor layer has a concave part, and

wherein at least one of the first gate electrode and the second gate electrode is formed in the concave part.

5. The semiconductor device according to claim 4 ,

wherein a gate length of the first gate electrode is shorter than a gate length of the second gate electrode.

6. The semiconductor device according to claim 5 ,

wherein the first facing part is located at a deeper position in the semiconductor layer than the second facing part.

7. The semiconductor device according to claim 6 ,

wherein the semiconductor layer further includes an electron transit layer and an electron supply layer disposed over the electron transit layer,

wherein the concave part in which the first gate electrode is formed passes through the electron supply layer and extends within the electrode transit layer, and

wherein the concave part in which the second gate electrode is formed is formed in the electron supply layer without passing through the electron supply layer.

8. The semiconductor device according to claim 7 ,

wherein the first facing part is disposed inside the second facing part.

9. The semiconductor device according to claim 7 ,

wherein the first gate electrode and the second gate electrode are integrated.