III-nitride devices including a graded depleting layer
A III-N device includes a III-N layer structure including a III-N channel layer, a III-N barrier layer over the III-N channel layer, and a graded III-N layer over the III-N barrier layer having a first side adjacent to the III-N barrier layer and a second side opposite the first side; a first power electrode and a second power electrode; and a gate between the first and second power electrodes, the gate being over the III-N layer structure. A composition of the graded III-N layer is graded so the bandgap of the graded III-N layer adjacent to the first side is greater than the bandgap of the graded III-N layer adjacent to the second side. A region of the graded III-N layer is (i) between the gate and the second power electrode, and (ii) electrically connected to the first power electrode and electrically isolated from the second power electrode.
1. A III-N device, comprising:
a III-N layer structure comprising a III-N channel layer over a graded III-N layer, and a III-N barrier layer over the III-N channel layer;
a 2 DEG channel in the III-N channel layer;
a source electrode and a drain electrode;
a gate electrode between the source electrode and the drain electrode, the gate electrode being over the III-N layer structure; and
the graded III-N layer having a first side adjacent the III-N channel layer and a second side opposite the first side; wherein
a composition of the graded III-N layer is graded such that a bandgap of the graded III-N layer adjacent to the first side is less than the bandgap of the graded III-N layer adjacent to the second side; and
wherein the graded III-N layer is (i) between the gate electrode and the drain electrode, and a portion of the III-N channel layer is between the drain electrode and the graded III-N layer; and the graded III-N layer is (ii) between the source electrode and the gate electrode, and is electrically connected to the source electrode.
2. The device of claim 1 , wherein a grading profile of the graded III-N layer is such that a polarization charge density in the graded III-N layer is in a range of 10-100% of an areal sheet charge density of mobile charge in the 2 DEG channel.
3. The device off claim 1 , wherein the source electrode extends through an entire thickness of the III-N channel layer to contact the graded III-N layer.
4. The device of claim 1 , wherein the graded III-N layer is formed of Al y Ga 1−y N (0≤y≤1), where y decreases from the second side opposite the III-N channel layer to the first side.
5. The device of claim 1 , wherein the graded III-N layer comprises a first graded III-N layer adjacent to the first side and a second graded III-N layer adjacent to the second side, wherein the second graded III-N layer is thicker than the first graded III-N layer.
6. The device of claim 5 , wherein a bandgap of the first graded III-N layer is graded at a first rate, and a bandgap of the second graded III-N layer is graded at a second rate, the first rate being greater than the second rate.
7. The III-N device of claim 6 , wherein the first rate is at least five times greater than the second rate.
8. A III-N device, comprising:
a III-N layer structure comprising a III-N channel layer over a graded III-N layer, and a III-N barrier layer over the III-N channel layer;
a 2 DEG channel in the III-N channel layer;
a source electrode and a drain electrode;
a gate electrode between the source electrode and the drain electrode, the gate electrode being over the III-N layer structure; and
the graded III-N layer having a first side adjacent the III-N channel layer and a second side opposite the first side; and
a composition of the graded III-N layer causes the graded III-N layer to have a net negative polarization charge; and
wherein the graded III-N layer is (i) between the gate electrode and the drain electrode, and a portion of the III-N channel layer is between the drain electrode and the graded III-N layer; and the graded III-N layer is (ii) between the source electrode and the gate electrode, and is electrically connected to the source electrode.
9. The device of claim 8 , wherein the graded III-N layer comprises a first graded III-N layer adjacent to the first side and a second graded III-N layer adjacent to the second side, wherein the second graded III-N layer is thicker than the first graded III-N layer.
10. The device of claim 9 , wherein the second graded III-N layer is at least three times thicker than the first graded III-N layer.
11. The III-N device of claim 10 , wherein a bandgap of the first graded III-N layer is graded at a first rate, and a bandgap of the second graded III-N layer is graded at a second rate, the first rate being greater than the second rate.
12. The III-N device of claim 11 , wherein the first rate is at least five times greater than the second rate.
13. A III-N device, comprising:
a III-N layer structure comprising a III-N channel layer and a III-N barrier layer over a graded III-N layer;
a 2 DEG channel in the III-N channel layer;
a source electrode and a drain electrode;
a gate electrode between the source electrode and the drain electrode, the gate electrode being over the III-N layer structure; and
the graded III-N layer having a first side adjacent the III-N channel layer and a second side opposite the first side; wherein
a composition of the graded III-N layer is graded such that a bandgap of the graded III-N layer adjacent to the first side is less than the bandgap of the graded III-N layer adjacent to the second side; and
wherein the graded III-N layer is (i) between the gate electrode and the drain electrode; and (ii) at least partially below the source electrode; and
a p-doped III-N layer over the graded III-N layer having a third side contacting the graded III-N layer, and a fourth side contacting the source electrode.
14. The device of claim 13 , wherein the graded III-N layer is formed of Al y Ga 1−y N (0≤y≤1), where y decreases from the second side opposite the III-N channel layer to the first side.
15. The device of claim 13 , wherein the p-doped III-N layer is doped by ion implanting p-type dopants prior to forming the source electrode.
16. The device of claim 13 , wherein a grading profile of the graded III-N layer is such that a polarization charge density in the graded III-N layer is in a range of 10-100% of an areal sheet charge density of mobile charge in the 2 DEG channel.
17. The device off claim 13 , wherein the source electrode extends through an entire thickness of the III-N channel layer to contact the p-doped III-N layer.
18. The device of claim 17 , wherein the graded III-N layer is not electrically connected to the drain electrode.
19. The device of claim 18 , wherein a portion of the III-N channel layer is below the drain electrode and said portion is between the graded III-N layer and the drain electrode.