High electron mobility transistor structure with improved breakdown voltage performance
A high electron mobility transistor (HEMT) includes a silicon substrate, an unintentionally doped gallium nitride (UID GaN) layer over the silicon substrate. The HEMT further includes a donor-supply layer over the UID GaN layer, a gate structure, a drain, and a source over the donor-supply layer. The HEMT further includes a dielectric layer having one or more dielectric plug portions in the donor-supply layer and top portions between the gate structure and the drain over the donor-supply layer. A method for making the HEMT is also provided.
1. A high electron mobility transistor (HEMT) comprising:
a silicon substrate;
an unintentionally doped gallium nitride (UID GaN) layer over the substrate;
a donor-supply layer over the UID GaN layer;
a gate structure, a drain, and a source over the donor-supply layer, said gate structure disposed between the drain and the source; and
a dielectric layer over the donor-supply layer between the gate structure and the drain, the dielectric layer having one or more first portions in the donor-supply layer and a second portion over the one or more first portions and the donor-supply layer,
wherein at least one of the one or more first portions is proximate to the gate, and a thickness of a portion of the donor-supply layer under the one or more first portions of the dielectric layer is at least 40% of a thickness of a portion of the donor-supply layer directly under the second portion of the dielectric layer.
2. The HEMT of claim 1 , wherein the dielectric layer comprises zinc oxide, zirconium oxide, hafnium oxide or titanium oxide.
3. The HEMT of claim 1 , wherein the dielectric layer comprises silicon oxide, silicon nitride, silicon oxynitride, carbon doped silicon oxide, carbon doped silicon nitride or carbon doped silicon oxynitride.
4. The HEMT of claim 1 , wherein a thickness of a portion of the donor-supply layer under the one or more first portions of the dielectric layer is at least 15 nanometers.
5. The HEMT of claim 1 , wherein the one or more first portions of the dielectric layer is one first portion and wherein an area of the first portion is about 5% to about 20% of an area of a drift region of the donor-supply layer.
6. The HEMT of claim 1 , wherein the at least one of the one or more first portions adjoins a gate edge.
7. The HEMT of claim 1 , wherein the one or more first portions of the dielectric layer are quadrilaterals in a top view.
8. The HEMT of claim 1 , the one or more first portions of the dielectric layer and portion of the donor-supply layer surrounding the one or more first portions of the dielectric layer form a checkered pattern.
9. The HEMT of claim 1 , wherein the one or more first portions of the dielectric layer cover about 40% to about 75% of the portion of the donor-supply layer between the gate structure and the drain.
10. The HEMT of claim 1 , wherein a largest of the one or more first portions of the dielectric layer is proximate to the gate.
11. The HEMT of claim 1 , wherein the donor-supply layer comprises undoped aluminum nitride or undoped aluminum gallium nitride.
12. The HEMT of claim 1 , wherein a thickness of the one or more first portions of the dielectric layer is about 3 nanometers to about 10 nanometers.
13. A high electron mobility transistor (HEMT) comprising:
a substrate;
a gallium nitride (GaN) layer over the substrate;
a donor-supply layer over the GaN layer, the donor-supply layer having at least one opening, the at least one opening having a first width;
a gate structure, a drain, and a source over the donor-supply layer, said gate structure between the drain and the source, wherein at least a portion of the gate structure is outside of each opening of the at least one opening; and
a dielectric layer over the donor-supply layer between the gate structure and the drain, the dielectric layer having a first portion filling the at least one opening and a second portion over a top surface of the donor-supply layer.
14. The HEMT of claim 13 , wherein the dielectric layer is between the gate structure and the source and the dielectric layer between the gate structure and the source is over the top surface of the donor-supply layer.
15. The HEMT of claim 13 , wherein the dielectric layer extends under a portion of the gate structure.
16. The HEMT of claim 13 , wherein a distance from the gate structure to the at least one opening is less than the first width.
17. A high electron mobility transistor (HEMT) comprising:
a substrate;
an unintentionally doped gallium nitride (UID GaN) layer over the substrate;
an Al x Ga (1-x) N layer over the UID GaN layer, the Al x Ga (1-x) N layer having at least one opening;
a gate structure, a drain, and a source over the Al x Ga (1-x) N layer, said gate structure between the drain and the source, wherein a bottom surface of the gate structure is in direct contact with the Al x Ga (1-x) N layer; and
a dielectric layer over the Al x Ga (1-x) N layer, the dielectric layer having a first portion between the gate structure and the drain filling the at least one opening, and a second portion between the gate structure and the source over a top surface of the Al x Ga (1-x) N layer.
18. The HEMT of claim 17 , wherein x ranges from about 0.1 to about 1.0.
19. The HEMT of claim 17 , wherein the drain and the source are embedded in the UID GaN layer.
20. The HEMT of claim 1 , wherein the gate structure is offset with respect to the one or more first portions.