Drain ledge for self-aligned gate and independent channel region and drain-side ridges for SLCFET

1. A transistor device, comprising:

a base structure;

a superlattice of conducting channels overlying the base structure and including:

source and drain access regions spaced-apart from each other;

a ledge, formed in the superlattice of conducting channels, between and spaced-apart from the source and drain access regions; and

source-side alternating multichannel ridges and trenches that extend from the source access region to the ledge, each ridge having a topside and opposing sidewalls that each extend from the ledge to the source access region, wherein the ledge is transverse to the source-side alternating multichannel ridges and trenches; and

gate metal that covers each ridge continuously from the ledge to the source access region, such that the gate metal completely covers the topside of the ridge and edges of the conducting channels that intersect the sidewalls of the ridge.

2. The transistor device of claim 1 , wherein:

the source and drain access regions are spaced-apart from each other along a length direction;

the alternating ridges and trenches extend along the length direction and undulate along a width direction that is transverse to the length direction; and

the ledge extends continuously along the width direction.

3. The transistor device of claim 1 , wherein:

the ledge includes a sidewall forming a boundary between the ledge and the source-side alternating multichannel ridges and trenches and configured to constrain the gate metal to the source-side alternating multichannel ridges and trenches; and

the gate metal covers the sidewall of the ledge, such that the gate metal completely covers edges of the conducting channels that intersect the sidewall of the ledge.

4. The transistor device of claim 1 , wherein the superlattice of conducting channels further includes drain-side alternating multichannel ridges and trenches that extend from the ledge to the drain access region.

5. The transistor device of claim 1 , wherein the gate metal includes a conformal metal layer that covers the topside and the sidewalls of each multichannel ridge.

6. The transistor device of claim 5 , wherein the conformal metal layer continuously covers the topside and the sidewalls of each multichannel ridge, and each trench, completely, from the ledge to the source access region.

7. The transistor device of claim 1 , wherein the gate metal includes metal configured as a T-gate that completely fills each trench and covers the topside and sidewalls of each multichannel ridge.

8. The transistor device of claim 1 , wherein the source and drain access region each have a substantially planar configuration without alternating multichannel ridges and trenches.

9. The transistor device of claim 1 , wherein a spacing between the ledge and the source access region defines a length of the gate.

10. The transistor device of claim 1 , wherein the opposing sidewalls of each multichannel ridge are tapered toward each other such that a separation between the sidewalls decreases as the sidewalls rise from the base structure to the topside of the multichannel ridge.

11. The transistor device of claim 1 , wherein the gate metal completely fills each trench from a nadir of the trenches to a full height of the multichannel ridges above the base structure.

12. The transistor device of claim 1 , wherein the conducting channels include two-dimensional electron gas (2DEG) channels.

13. The transistor device of claim 1 , wherein the superlattice comprises heterostructures that form the conducting channels.

14. The transistor device of claim 13 , wherein each heterostructure includes an AlGaN layer and a GaN layer.

15. The transistor device of claim 1 , wherein the transistor device is configured as a field effect transistor (FET).

16. A method of forming a transistor device, comprising:

forming a base structure;

forming a superlattice of conducting channels overlying the base structure and including:

source and drain access regions spaced-apart from each other;

a ledge, formed in the superlattice of conducting channels, between and spaced-apart from the source and drain access regions; and

source-side alternating multichannel ridges and trenches that extend from the source access region to the ledge, each ridge having a topside and opposing sidewalls that each extend from the ledge to the source access region, wherein the sidewalls intersect edges of the conducting channels of the ridge, wherein the ledge is transverse to the source-side alternating multichannel ridges and trenches; and

forming gate metal on each ridge continuously from the ledge to the source access region, such that the gate metal completely covers the topside of the ridge and the edges of the conducting channels that intersect the sidewalls of the ridge from the ledge to the source access region.

17. The method of claim 16 , wherein:

the source and drain access regions are spaced-apart from each other along a length direction;

the alternating ridges and trenches extend along the length direction and undulate along a width direction that is transverse to the length direction; and

the ledge extends continuously along the width direction.

18. The method of claim 16 , further comprising:

forming in the superlattice of conducting channels drain-side alternating multichannel ridges and trenches that extend from the ledge to the drain access region.

19. The method of claim 16 , wherein the step of forming gate metal includes forming the gate metal as a conformal metal layer that covers the topside and the sidewalls of each multichannel ridge.

20. The method of claim 19 , wherein the step of forming the gate metal includes forming the gate metal as a conformal metal layer that continuously covers the topside and the sidewalls of each multichannel ridge, and each trench, completely, from the ledge to the source access region.