Heterojunction transistors having barrier layer bandgaps greater than channel layer bandgaps and related methods

1. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a buffer layer comprising iron doped Group III nitride, wherein the channel layer is between the barrier layer and the buffer layer;

a gate contact on the barrier layer so that the barrier layer is between the gate contact and the channel layer;

source and drain contacts on opposite sides of the gate contact, wherein the source and drain contacts are spaced apart from the gate contact; and

an energy barrier comprising a layer of a Group III nitride between the channel layer and the buffer layer, wherein the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, wherein the layer of the Group III nitride of the energy barrier comprises a layer of an InN/GaN alloy, wherein a mole fraction of InN (indium nitride) in the InN/GaN alloy of the energy barrier is in the range of about 1% to about 50%, wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, the source and drain contacts, and the energy barrier is configured to provide a back confinement value of at least about 0.21 ohm mm 2 GHz, and wherein the energy barrier is silicon doped;

wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region.

2. A heterojunction transistor according to claim 1 wherein a mole fraction of InN (indium nitride) in an InN/GaN alloy of the energy barrier is in the range of about 4% to about 16%.

3. A heterojunction transistor according to claim 1 wherein a thickness of the energy barrier is in the range of about 0.1 nm to about 10 nm.

4. A heterojunction transistor according to claim 1 further comprising:

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer and a hole source region is induced at an interface between the hole source layer and the energy barrier.

5. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a gate contact on the barrier layer so that the barrier layer is between the gate contact and the channel layer;

source and drain contacts on opposite sides of the gate contact;

an energy barrier comprising a layer of a Group III nitride adjacent the channel layer, wherein the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, wherein the layer of the Group III nitride of the energy barrier comprises a layer of an InN/GaN alloy, wherein a mole fraction of InN (indium nitride) in the InN/GaN alloy of the energy barrier is in the range of about 1% to about 50%, and wherein the energy barrier is silicon doped; and

a buffer layer comprising an iron doped Group III nitride, wherein the energy barrier is between the channel layer and the buffer layer;

wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region.

6. A heterojunction transistor according to claim 5 wherein a mole fraction of InN (indium nitride) in an InN/GaN alloy of the energy barrier is in the range of about 4% to about 16%.

7. A heterojunction transistor according to claim 5 wherein a thickness of the energy barrier is in the range of about 0.1 nm to about 10 nm.

8. A heterojunction transistor according to claim 5 further comprising:

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer and a hole source region is induced at an interface between the hole source layer and the energy barrier.

9. A heterojunction transistor according to claim 5 further comprising:

a passivation layer on the barrier layer between the gate contact and the source contact and between the gate contact and the drain contact;

wherein the gate contact includes field plate regions extending laterally on surface portions of the passivation layer opposite the substrate towards the source and drain contacts; and

a cap layer comprising aluminum gallium nitride on the barrier layer wherein the barrier layer is between the channel layer and the cap layer, wherein the cap layer is between the barrier layer and the gate contact, wherein the cap layer is between the barrier layer and the source contact, and wherein the cap layer is between the barrier layer and the drain contact.

10. A heterojunction transistor according to claim 5 wherein the a buffer layer comprises iron doped gallium nitride.

11. A heterojunction transistor according to claim 5 further comprising:

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer, wherein a hole source region is induced at an interface between the hole source layer and the energy barrier, and wherein the hole source region is between the energy barrier and the buffer layer.

12. A heterojunction transistor according to claim 11 wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, wherein the energy barrier opposes movement of carriers away from the channel layer, and wherein the energy barrier has a narrower bandgap than the channel layer.

13. A heterojunction transistor according to claim 12 wherein a concentration of Al in the barrier layer is greater than a concentration of Al in the channel layer.

14. The heterojunction transistor according to claim 1 wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, and wherein the energy barrier opposes movement of electrons away from the channel layer.

15. The heterojunction transistor according to claim 14 wherein the channel layer comprises Al x Ga 1-x N (0≦x≦1), wherein the barrier layer comprises Al y Ga 1-y N (0<y≦1).

16. The heterojunction transistor according to claim 5 wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, and wherein the energy barrier opposes movement of electrons away from the channel layer.

17. The heterojunction transistor according to claim 16 wherein the channel layer comprises Al x Ga 1-x N (0≦x≦1), wherein the barrier layer comprises Al y Ga 1-y N (0<y≦1).

18. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a buffer layer comprising iron doped Group III nitride, wherein the channel layer is between the barrier layer and the buffer layer;

an energy barrier comprising a layer of a Group III nitride including indium adjacent the channel layer such that the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, and wherein the energy barrier is between the channel layer and the buffer layer; and

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer and a hole source region is induced at an interface between the hole source layer and the energy barrier, and wherein the hole source region is between the energy barrier and the buffer layer;

wherein the channel layer comprises Al x Ga 1-x N (0≦x≦1), wherein the barrier layer comprises Al y Ga 1-y N (0<y≦1), wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region, and wherein the energy barrier opposes movement of electrons away from the channel layer.

19. A heterojunction transistor according to claim 18 further comprising:

a gate contact on the barrier layer so that the barrier layer is between the gate contact and the channel layer; and

source and drain contacts on opposite sides of the gate contact, wherein the source and drain contacts are spaced apart from the gate contact.

20. A heterojunction transistor according to claim 19 wherein the buffer layer comprises iron doped gallium nitride.

21. A heterojunction transistor according to claim 19 wherein the barrier layer comprises aluminum nitride, the heterojunction transistor further comprising:

a cap layer comprising aluminum gallium nitride on the barrier layer wherein the barrier layer is between the channel layer and the cap layer, wherein the cap layer is between the barrier layer and the gate contact, wherein the cap layer is between the barrier layer and the source contact, and wherein the cap layer is between the barrier layer and the drain contact.

22. A heterojunction transistor according to claim 19 further comprising:

a passivation layer on the barrier layer between the gate contact and the source contact and between the gate contact and the drain contact;

wherein the gate contact includes field plate regions extending laterally on surface portions of the passivation layer opposite the substrate towards the source and drain contacts.

23. A heterojunction transistor according to claim 19 , wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide a back confinement value of at least about 0.21 ohm mm 2 GHz.

24. A heterojunction transistor according to claim 19 wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide a device resistance of at least about 9 ohm mm.

25. A heterojunction transistor according to claim 19 wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide at least 50% power added efficiency and at least 7 W/mm output power.

26. A heterojunction transistor according to claim 19 wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide at least 65% power added efficiency and at least 8 W/mm output power at a frequency of at least 10 GHz.

27. A heterojunction transistor according to claim 23 wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide the back confinement value of at least approximately 0.21 ohm mm 2 GHz with a unity gain frequency of at least about 35 GHz.

28. A heterojunction transistor according to claim 23 wherein the heterojunction transistor comprising the channel layer, the barrier layer, the gate contact, and the source and drain contacts is configured to provide a back confinement value of at least approximately 0.3 ohm mm 2 GHz.

29. A heterojunction transistor according to claim 18 wherein the energy barrier is silicon doped.

30. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a gate contact on the barrier layer so that the barrier layer is between the gate contact and the channel layer;

source and drain contacts on opposite sides of the gate contact;

an energy barrier comprising a layer of a Group III nitride adjacent the channel layer, wherein the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, wherein the layer of the Group III nitride of the energy barrier comprises a layer of an InN/GaN alloy, and wherein a mole fraction of InN (indium nitride) in the InN/GaN alloy of the energy barrier is in the range of about 1% to about 50%;

a buffer layer comprising an iron doped Group III nitride, wherein the energy barrier is between the channel layer and the buffer layer; and

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer, wherein a hole source region is induced at an interface between the hole source layer and the energy barrier, and wherein the hole source region is between the energy barrier and the buffer layer;

wherein the channel layer comprises Al x Ga 1-x N (0≦x≦1), wherein the barrier layer comprises Al y Ga 1-y N (0<y≦1), wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region, and wherein the energy barrier opposes movement of electrons away from the channel layer.

31. A heterojunction transistor according to claim 30 wherein the energy barrier is silicon doped.

32. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a buffer layer comprising iron doped Group III nitride, wherein the channel layer is between the barrier layer and the buffer layer;

an energy barrier comprising a layer of a Group III nitride including indium adjacent the channel layer such that the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, and wherein the energy barrier is between the channel layer and the buffer layer; and

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer and a hole source region is induced at an interface between the hole source layer and the energy barrier, and wherein the hole source region is between the energy barrier and the buffer layer;

wherein the channel layer comprises InAlGaN, wherein the barrier layer comprises InAlGaN, wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, and wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region.

33. A heterojunction transistor comprising:

a channel layer comprising a Group III nitride;

a barrier layer comprising a Group III nitride on the channel layer wherein the barrier layer has a bandgap greater than a bandgap of the channel layer;

a gate contact on the barrier layer so that the barrier layer is between the gate contact and the channel layer;

source and drain contacts on opposite sides of the gate contact;

an energy barrier comprising a layer of a Group III nitride adjacent the channel layer, wherein the channel layer is between the barrier layer and the energy barrier, wherein the energy barrier has a narrower bandgap than the channel layer, wherein the layer of the Group III nitride of the energy barrier comprises a layer of an InN/GaN alloy, and wherein a mole fraction of InN (indium nitride) in the InN/GaN alloy of the energy barrier is in the range of about 1% to about 50%;

a buffer layer comprising an iron doped Group III nitride, wherein the energy barrier is between the channel layer and the buffer layer; and

a hole source layer comprising a Group III nitride adjacent the energy barrier such that the energy barrier is between the channel layer and the hole source layer, wherein a hole source region is induced at an interface between the hole source layer and the energy barrier, and wherein the hole source region is between the energy barrier and the buffer layer;

wherein the channel layer comprises InAlGaN, wherein the barrier layer comprises InAlGaN, wherein the barrier layer and the channel layer cooperatively induce a two-dimensional electron gas at an interface between the channel layer and the barrier layer, and wherein the energy barrier comprises a fully depleted, delta doped electron source layer in proximity with and spaced apart from a fully depleted, delta doped hole source layer by a high field region.