Methods of fabricating gallium nitride semiconductor layers on substrates including non-gallium nitride posts, and gallium nitride semiconductor structures fabricated thereby
A substrate includes non-gallium nitride posts that define trenches therebetween, wherein the non-gallium nitride posts include non-gallium nitride sidewalls and non-gallium nitride tops and the trenches include non-gallium floors. Gallium nitride is grown on the non-gallium nitride posts, including on the non-gallium nitride tops. Preferably, gallium nitride pyramids are grown on the non-gallium nitride tops and gallium nitride then is grown on the gallium nitride pyramids. The gallium nitride pyramids preferably are grown at a first temperature and the gallium nitride preferably is grown on the pyramids at a second temperature that is higher than the first temperature. The first temperature preferably is about 1000° C. or less and the second temperature preferably is about 1100° C. or more. However, other than temperature, the same processing conditions preferably are used for both growth steps. The grown gallium nitride on the pyramids preferably coalesces to form a continuous gallium nitride layer. Accordingly, gallium nitride may be grown without the need to form masks during the gallium nitride growth process. Moreover, the gallium nitride growth may be performed using the same processing conditions other than temperatures changes. Accordingly, uninterrupted gallium nitride growth may be performed.
1. A semiconductor structure comprising:
a substrate comprising a first material, the substrate including a plurality of posts that comprise the first material and that define trenches therebetween, the posts including sidewalls and tops that comprise the first material, and the trenches including floors that comprise the first material;
a conformal buffer layer on the substrate including on the sidewalls, the tops and the floors; and
a layer of nitride based semiconductor material over the posts including on the tops that comprise the first material, wherein the layer of the nitride based semiconductor material is on the conformal buffer layer opposite the substrate.
2. A structure according to claim 1 wherein the layer of second semiconductor material comprises pyramids of the second semiconductor material on the tops.
3. A structure according to claim 1 wherein the layer of second semiconductor material fills the trenches.
4. A structure according to claim 1 wherein the structure is free of masking layers therein.
5. A structure according to claim 1 wherein the sidewalls expose a 11{overscore (2)}0 plane of the first material.
6. A structure according to claim 1 , wherein the first material comprises silicon.
7. A structure according to claim 1 , wherein the first material comprises silicon carbide.
8. A structure according to claim 1 , wherein the first material comprises sapphire.
9. A structure according to claim 1 , wherein the substrate consists essentially of a single material.
10. A structure according to claim 1 , wherein the layer of second semiconductor material includes a region having a first defect density and a region having a second defect density lower than the first defect density.
11. A structure according to claim 10 , wherein the second defect density is less than or equal to about 10 5 cm −2 .
12. A structure according to claim 10 , wherein the first defect density is greater than or equal to about 10 8 cm −2 .
13. A structure according to claim 10 , wherein the region having the second defect density is laterally grown.
14. A structure according to claim 1 , wherein the conformal buffer layer comprises gallium nitride.
15. A structure according to claim 1 , wherein the conformal buffer layer comprises aluminum nitride.
16. A structure according to claim 1 , wherein the conformal buffer layer comprises silicon carbide.