Normally-off high electron mobility transistor

1. A normally-off high electron mobility transistor (HEMT) comprising:

a channel layer including a first nitride semiconductor;

a channel supply layer on the channel layer,

the channel supply layer including a second nitride semiconductor,

the channel supply layer configured to induce a two-dimensional electron gas (2DEG) in the channel layer;

a source electrode and a drain electrode at sides of the channel supply layer;

a depletion-forming layer on the channel supply layer,

the depletion-forming layer configured to form a depletion region in at least a partial region of the 2DEG,

the depletion-forming layer having at least two thicknesses;

a gate insulation layer on the depletion-forming layer; and

a gate electrode on the gate insulation layer,

the gate electrode contacting the depletion-forming layer,

wherein

the gate insulation layer defines an opening that exposes a top surface of the depletion-forming layer, and

the gate electrode contacts the top surface of the depletion-forming layer through the opening.

2. The normally-off HEMT of claim 1 , wherein

the depletion-forming layer includes a first part having a first thickness, and

the depletion-forming layer includes a second part at a side of the first part and,

the depletion-forming layer includes a third part at a different side of the first part,

the second part and the third part having a second thickness.

3. The normally-off HEMT of claim 2 , wherein the first thickness is thicker than the second thickness.

4. The normally-off HEMT of claim 2 , wherein

the first part of the depletion-forming layer is a strip shape,

the second part and the third part of the depletion-forming layer are a strip shape in parallel to the first part.

5. The normally-off HEMT of claim 2 , wherein the second part and the third part are spaced apart from the source electrode and the drain electrode, respectively.

6. The normally-off HEMT of claim 5 , wherein

the first part of the depletion-forming layer is configured to form the depletion region below the first part, and

an electron density of the 2DEG below at least one of the second part and the third part of the depletion-forming layer is relatively lower than an electron density of the 2DEG that is not located below the depletion-forming layer.

7. The normally-off HEMT of claim 2 , wherein at least one of the second part and the third part of the depletion-forming layer contacts a corresponding one of the source electrode and the drain electrode.

8. The normally-off HEMT of claim 2 , wherein the gate electrode is on the gate insulation layer above at least a portion of the first to third parts of the depletion-forming layer.

9. The normally-off HEMT of claim 2 , wherein the opening in the gate insulation layer is on the first part of the depletion-forming layer.

10. A normally-off high electron mobility transistor (HEMT) comprising:

a channel layer including a first nitride semiconductor;

a channel supply layer on the channel layer,

the channel supply layer including a second nitride semiconductor,

the channel supply layer configured to induce a two-dimensional electron gas (2DEG) in the channel layer;

a source electrode and a drain electrode at sides of the channel supply layer;

a depletion-forming layer on the channel supply layer,

the depletion-forming layer configured to form a depletion region in at least a partial region of the 2DEG,

the depletion-forming layer having at least two thicknesses,

the depletion-forming layer including a first part having a first thickness,

the depletion-forming layer including a second part at a side of the first part and,

the depletion-forming layer including a third part at a different side of the first part,

the second part and the third part having a second thickness;

a gate insulation layer on the depletion-forming layer;

a gate electrode on the gate insulation layer,

the gate electrode contacting the depletion-forming layer; and

a first gate electrode between the first part and the gate insulation layer,

wherein the first gate electrode and the gate electrode are electrically connected to each other.

11. The normally-off HEMT of claim 10 , further comprising:

a wire that electrically connects the first gate electrode and the gate electrode, wherein

the gate insulation layer exposes the first gate electrode.

12. The normally-off HEMT of claim 10 , wherein

the gate insulation layer defines an opening that exposes the first gate electrode, and

the first gate electrode and the gate electrode are electrically connected to each other through the opening.

13. The normally-off HEMT of claim 1 , wherein the first nitride semiconductor includes a gallium nitride (GaN) group material.

14. The normally-off HEMT of claim 1 , wherein the second nitride semiconductor includes a nitride including at least one of aluminum (Al), gallium (Ga), indium (In) and boron (B).

15. The normally-off HEMT of claim 1 , wherein the depletion-forming layer includes a p-type nitride semiconductor.

16. The normally-off HEMT of claim 15 , wherein the depletion-forming layer includes a group III-V nitride semiconductor material.

17. The normally-off HEMT of claim 1 , wherein

the depletion-forming layer includes a first part having a first thickness,

the depletion-forming layer includes a second part having a second thickness that is different than the first thickness,

the first part of the depletion-forming layer separates the gate electrode and the channel supply layer by a greater distance than the second part of the depletion-forming layer separates the gate electrode and the channel supply layer.

18. The normally-off HEMT of claim 1 , wherein

the channel supply layer includes a first sidewall opposite a second sidewall, and

the source and drain electrodes contact the first sidewall and second sidewall of the channel supply layer respectively.