Gallium nitride power semiconductor device having a vertical structure

1. A semiconductor device, comprising:

a substrate having first and second sides;

a first active layer disposed over the first side of the substrate;

a second active layer disposed on the first active layer, the second active layer having a higher bandgap than the first active layer such that a two-dimensional electron gas layer arises between the first active layer and the second active layer;

at least one trench extending through the first and second active layers and the two-dimensional electron gas layer and into the substrate;

a conductive material lining the trench;

a first electrode disposed on the second active layer; and

a second electrode disposed on the second side of the substrate;

a third electrode disposed on the second active layer, said first, second and third electrodes being source, drain and gate electrodes, respectively.

2. The semiconductor device of claim 1 , wherein the at least one trench comprises a pair of trenches extending through the first and second active layers and the two-dimensional electron gas layer and into the substrate, each of the trenches being lined with a conductive material.

3. The semiconductor device of claim 1 , wherein the first active layer includes an epitaxial layer.

4. The semiconductor device of claim 1 , wherein the first electrode is a Schottky contact.

5. The semiconductor device of claim 4 , wherein the second electrode is an Ohmic contact.

6. The semiconductor device of claim 1 , wherein the first active layer comprises a group III nitride semiconductor material.

7. The semiconductor device of claim 6 , wherein the first active layer comprises GaN.

8. The semiconductor device of claim 1 , wherein the second active layer comprises a group III nitride semiconductor material.

9. The semiconductor device of claim 8 , wherein the second active layer comprises Al X Ga 1-X N, wherein 0<X<1.

10. The semiconductor device of claim 1 , further comprising a dielectric layer disposed between each of the third electrodes and the second active layer.

11. The semiconductor device of claim 1 , wherein the third electrodes are Schottky electrodes.

12. The semiconductor device of claim 1 , further comprising a passivation material filling the trench.

13. A method of forming a semiconductor device, comprising:

forming a first active layer on a substrate;

forming a second active layer over the first active layer, the second active layer having a higher bandgap than the first active layer such that a two-dimensional electron gas layer arises between the first active layer and the second active layer;

forming at least one trench that extends through the first and second active layers and the two-dimensional electron gas layer and into the substrate;

lining the trench with a conductive material;

filling the trench with a passivation material;

forming a first electrode on the second active layer; and

forming a second electrode on a bottom side of the substrate;

forming a third electrode disposed on the second active layer, said first, second and third electrodes being source, drain and gate electrodes, respectively.

14. The method of claim 13 , wherein the at least one trench comprises a pair of trenches and further comprising forming a the pair of trenches so that each of the trenches extend through the first and second active layers and the two-dimensional electron gas layer and into the substrate, each of the trenches being lined with a conductive material and filled with a passivation material.

15. The method of claim 13 , wherein the first electrode is a Schottky contact.

16. The method of claim 15 , wherein the second electrode is an Ohmic contact.

17. The method of claim 13 , wherein the first active layer comprises a group III nitride semiconductor material.