Nitride-based transistors with a protective layer and a low-damage recess

1. A high electron mobility transistor comprising:

a nitride-based channel layer on a substrate;

a nitride-based semiconductor barrier layer on the nitride-based channel layer, the nitride based semiconductor barrier layer having a sheet resistance after a high temperature anneal that is substantially the same as a sheet resistance of the nitride-based semiconductor barrier layer before the high temperature anneal;

ohmic contacts on the barrier layer;

a gate contact on the barrier layer;

a protective layer disposed on the barrier layer that is adjacent and spaced apart from the ohmic contacts and that the gate contact extends through;

a passivation layer on the protective layer and that substantially fills a gap between the ohmic contacts and the protective layer.

2. The high electron mobility transistor of claim 1 , wherein the passivation layer is also on the protective layer and wherein the gate contact extends through the protective layer and the passivation layer.

3. The high electron mobility transistor of claim 1 , wherein at least a portion of the gate contact is directly on the protective layer and a portion of the gate contact is directly on the barrier layer.

4. The high electron mobility transistor of claim 1 , further comprising a passivation layer on the barrier layer that substantially fills a gap between the ohmic contacts and the gate contact.

5. The high electron mobility transistor of claim 1 :

wherein the nitride-based channel layer comprises a Group III-nitride layer; and

wherein the nitride-based semiconductor barrier layer comprises a Group III-nitride layer.

6. The high electron mobility transistor of claim 1 , wherein the channel layer has a lower bandgap than the barrier layer.

7. The high electron mobility transistor of claim 1 , wherein the channel layer comprises an undoped layer having a thickness of greater than about 20 Å.

8. The high electron mobility transistor of claim 1 , wherein the channel layer comprises a superlattice and/or a combination of Group III-nitride layers.

9. The high electron mobility transistor of claim 1 :

wherein the channel layer comprises aluminum gallium nitride (AlGaN), gallium nitride (GaN), indium gallium nitride (InGaN), and/or aluminum indium gallium nitride (AlInGaN); and

wherein the barrier layer comprises aluminum nitride (AlN), aluminum indium nitride (AlInN), AlGaN, GaN, InGaN, and/or AlInGaN.

10. The high electron mobility transistor of claim 1 , wherein the barrier layer comprises Al x Ga 1-x N wherein 0<x<1.

11. The high electron mobility transistor of claim 1 , wherein the barrier layer comprises multiple layers.

12. The high electron mobility transistor of claim 1 , further comprising a buffer layer on the substrate, and wherein the nitride-based channel layer is disposed on the buffer layer.

13. The high electron mobility transistor of claim 1 , wherein the protective layer has a thickness at least as thick as the ohmic contacts.

14. The high electron mobility transistor of claim 1 , wherein the ohmic contacts have a contact resistance of less than about 1 Ω-mm.

15. A high electron mobility transistor, comprising:

a nitride-based channel layer on a substrate;

a nitride-based semiconductor barrier layer on the nitride-based channel layer;

a protective layer on the barrier layer;

ohmic contacts on the barrier layer, adjacent and spaced apart from the protective layer so as to provide a gap between the ohmic contacts and the protective layer;

a gate contact on the barrier layer and extending through the protective layer; and

a passivation layer on the protective layer and that substantially fills the gap between the ohmic contacts and the protective layer.

16. The high electron mobility transistor of claim 15 :

wherein the nitride-based channel layer comprises a Group III-nitride layer; and

wherein the nitride-based semiconductor barrier layer comprises a Group III-nitride layer.

17. The high electron mobility transistor of claim 15 , wherein the channel layer has a lower bandgap than the barrier layer.

18. The high electron mobility transistor of claim 15 , wherein the channel layer comprises an undoped layer having a thickness of greater than about 20 Å.

19. The high electron mobility transistor of claim 15 , wherein the channel layer comprises a superlattice and/or a combination of Group III-nitride layers.

20. The high electron mobility transistor of claim 17 :

wherein the channel layer comprises aluminum gallium nitride (AlGaN), gallium nitride (GaN), indium gallium nitride (InGaN), and/or aluminum indium gallium nitride (AlInGaN); and

wherein the barrier layer comprises aluminum nitride (AlN), aluminum indium nitride (AlInN), AlGaN, GaN, InGaN, and/or AlInGaN.

21. The high electron mobility transistor of claim 15 , wherein the barrier layer comprises Al x Ga 1-x N wherein 0<x<1.

22. The high electron mobility transistor of claim 15 , wherein the barrier layer comprises multiple layers.

23. The high electron mobility transistor of claim 15 , further comprising a buffer layer on the substrate, and wherein the nitride-based channel layer is disposed on the buffer layer.

24. The high electron mobility transistor of claim 15 , wherein the protective layer is at least as thick as the ohmic contacts.

25. The high electron mobility transistor of claim 15 , wherein the gate contact is directly on the protective layer.

26. The high electron mobility transistor of claim 15 , wherein the protective layer has at thickness of about two monolayers.

27. The high electron mobility transistor of claim 1 , wherein the high temperature anneal is performed at a temperature of greater than about 900° C.

28. The high electron mobility transistor of claim 1 , wherein the high temperature anneal is an ohmic contact anneal that reduces the resistance of the ohmic contacts from a high resistance to less than about 1 Ω-mm.