High electron mobility transistor and method of driving the same

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

a channel layer including a first semiconductor material;

a channel supply layer on the channel layer,

the channel supply layer including a second semiconductor material,

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 both 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 the 2DEG;

a first gate electrode on the depletion-forming layer,

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

at least one second gate electrode separated from the first gate electrode on the depletion-forming layer and between the source electrode and the drain electrode.

2. The HEMT of claim 1 , wherein

the HEMT includes one second gate electrode,

the second gate electrode is a floating electrode, and

the first and second gate electrodes are configured such that applying a first gate voltage to the first gate electrode induces a second gate voltage in the second gate electrode.

3. The HEMT of claim 2 , wherein

the first gate electrode and the second gate electrode are connected to each other by the depletion-forming layer, and

the first gate electrode is configured to induce the second gate voltage in the second gate electrode via the depletion-forming layer if the first gate voltage is applied to the first gate electrode.

4. The HEMT of claim 3 , wherein the depletion-forming layer is a strip shape between the first gate electrode and the second gate electrode.

5. The HEMT of claim 3 , wherein the second gate electrode and the source electrode are connected to each other by the depletion-forming layer.

6. The HEMT of claim 5 , wherein the depletion-forming layer is a strip shape between the source electrode and the second gate electrode.

7. The HEMT of claim 2 , further comprising:

a coating layer on at least a portion of an upper surface of the channel supply layer.

8. The HEMT of claim 7 , wherein a material of the coating layer is the same as a material of the depletion-forming layer.

9. The HEMT of claim 8 , wherein a thickness of the coating layer is less than a thickness of the depletion-forming layer.

10. The HEMT of claim 2 , wherein the first gate electrode is configured to induce the second gate voltage in the second gate electrode via an upper surface of the channel supply layer.

11. The HEMT of claim 2 , wherein the second gate voltage induced in the second gate electrode is determined by the first gate voltage applied to the first gate electrode, a gap between the first gate electrode and the second gate electrode, and a gap between the second gate electrode and the source electrode.

12. The HEMT of claim 11 , wherein a threshold voltage of the HEMT is determined based on the second gate voltage induced in the second gate electrode.

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

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

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

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

17. A method of driving the HEMT of claim 1 , comprising:

applying a first gate voltage to the first gate electrode,

inducing a second gate voltage in a floating electrode by applying the first gate voltage to the first gate electrode,

wherein the HEMT includes one second gate electrode and the second gate electrode is the floating electrode.

18. The method of claim 17 , wherein the first gate electrode and the second gate electrode are connected to each other by the depletion-forming layer.

19. The method of claim 18 , wherein the second gate electrode and the source electrode are connected to each other by the depletion-forming layer.

20. The method of claim 17 , wherein the HEMT further includes a coating layer on at least a portion of an upper surface of the channel supply layer.

21. The method of claim 17 , wherein applying the first gate voltage to the first gate electrode induces the second gate voltage in the second gate electrode via an upper surface of the channel supply layer.

22. The method of claim 17 , wherein a threshold voltage of the HEMT is determined by the second gate voltage induced in the second gate electrode.

23. The method of claim 17 , wherein the second gate voltage induced in the second gate electrode is determined by the first gate voltage applied to the first gate electrode, a gap between the first gate electrode and the second gate electrode, and a gap between the second gate electrode and the source electrode.

24. The HEMT of claim 1 , wherein the at least one second gate electrode is one second gate electrode between the first gate electrode and the source electrode.

25. A high electron mobility transistor (HEMT) comprising:

a channel layer;

a channel supply layer on the channel layer,

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

a source electrode and a drain electrode spaced apart on the channel layer;

a depletion-forming layer on the channel supply layer,

the depletion-forming layer configured to form a depletion region in the 2DEG; and

a plurality of gate electrodes on the depletion-forming layer between the source electrode and the drain electrode,

the plurality of gate electrodes including a first gate electrode and a second gate electrode laterally spaced apart from each other.

26. The HEMT of claim 25 , wherein

the second gate electrode is a floating electrode between the source electrode and the first gate electrode, and

the first and second gate electrodes are configured such that applying a first gate voltage to the first gate electrode induces a second gate voltage in the second gate electrode.

27. The HEMT of claim 26 , wherein

the plurality of electrodes includes a third gate electrode on the depletion-forming layer, and

the third gate electrode is spaced apart between the second gate electrode and the source electrode.

28. The HEMT of claim 27 , wherein a portion of the depletion-forming layer extends between at least two of the first electrode, the second electrode, the third electrode, and the source electrode.

29. The HEMT of claim 26 , wherein a portion of the depletion-forming layer extends from the second gate electrode to at least one of the source electrode and the first gate electrode.

30. The HEMT of claim 26 , wherein the depletion forming layer exposes at least one of:

an entire upper surface of the channel supply layer between the source electrode and the second gate electrode,

an entire upper surface of the channel supply layer between the second gate electrode and the first gate electrode.

31. The HEMT of claim 26 , wherein at least one of the source electrode and the drain electrode is connected to a sidewall of the channel supply layer.

32. The HEMT of claim 26 , wherein the depletion forming layer has a grid shape.

33. The HEMT of claim 25 , wherein channel layer includes a group III-V compound semiconductor.

34. The HEMT of claim 25 , wherein a material of the channel supply layer is different than a material of the channel layer in terms of at least one of a polarization characteristic, an energy band gap, and a lattice constant.

35. The HEMT of claim 25 , wherein the depletion-forming layer includes a p-type semiconductor material.

36. The HEMT of claim 25 , wherein the second gate electrode is configured to raise a threshold voltage of the HEMT compared to a similar-formed HEMT that does not include the second gate electrode.

37. A method of driving the HEMT of claim 25 , comprising:

applying a first gate voltage to the first gate electrode; and

inducing a second gate voltage in the second gate electrode by applying the first gate voltage to the first gate electrode.

38. The method of claim 37 , wherein

the applying the first gate voltage includes forming a first channel under the first gate electrode in the channel layer, and

the first gate voltage is greater than a first threshold voltage for forming the first channel.

39. The method of claim 38 , wherein

the applying the first gate voltage induces the second gate voltage in the second gate electrode at a level that is greater than a second threshold voltage for forming a second channel under the second gate electrode in the channel layer, and

the applying the first gate voltage further includes forming the second channel under the second gate electrode in the channel layer.