Zirconium and hafnium boride alloy templates on silicon for nitride integration applications
Semiconductor structures are provided comprising a substrate and a epitaxial layer formed over the substrate, wherein the epitaxial layer comprises B; and one or more element selected from the group consisting of Zr, Hf and Al and has a thickness greater than 50 nm. Further, methods for integrating Group III nitrides onto a substrate comprising, forming an epitaxial buffer layer of a diboride of Zr, Hf, Al, or mixtures thereof, over a substrate; and forming a Group III nitride layer over the buffer layer, are provided which serve to thermally decouple the buffer layer from the underlying substrate, thereby greatly reducing the strain induced in the semiconductor structures upon fabrication and/or operation.
1. A method for forming an epitaxial buffer layer over a substrate by molecular beam epitaxy comprising:
contacting a substrate with a precursor gas at a temperature and a pressure suitable for depositing an epitaxial buffer layer over the substrate;
the epitaxial buffer layer having a thickness of greater than 100 nm and comprising ZrB 2 , AlB 2 , HfB 2 , Hf x Zr 1-x B 2 , Hf x Al 1-x B 2 , Zr x Al 1-x B 2 , or Zr z Hf y Al 1-z-y B 2 wherein the sum of z and y is less than or equal to 1;
wherein the precursor gas comprises (i) greater than 95% v/v hydrogen gas and (ii) 0.1-5% v/v of a precursor source, wherein the precursor source comprises Zr(BH 4 ) 4 , Hf(BH 4 ) 4 , an Al source, or mixtures thereof; and
wherein the use of the hydrogen gas reduces the surface roughness of the epitaxial layer by acting as a diluent to prevent the poisoning of the surface of the epitaxial layer with B-rich fragments.
2. The method of claim 1 wherein the substrate comprises a miscut Si(111) substrate.
3. The method of claim 1 wherein the temperature ranges from about 850° C. to about 950° C.
4. The method of claim 1 wherein the pressure ranges from about 1×10 −4 Torr to 1×10 −9 Torr.
5. The method of claim 1 , wherein the epitaxial buffer layer has a thickness of greater than about 200 nm.
6. The method of claim 1 , wherein the epitaxial buffer layer has a thickness of greater than about 400 nm.
7. The method of claim 1 , wherein the substrate comprises Si, Al 2 O 3 , SiC or GaAs.
8. The method of claim 7 wherein the substrate comprises Si (100) or Si(111).
9. The method of claim 1 , further comprising
forming a Group III nitride layer over the epitaxial buffer layer.
10. The method of claim 9 , wherein the epitaxial buffer layer has one or more properties selected from the group consisting of,
(i) thermally decoupled from the substrate;
(ii) a mismatch strain which is essentially thermally constant over a temperature range of room temperature to 900° C.;
(iii) relaxed at 900° C.; and
(iv) an atomically flat surface.
11. The method of claim 9 , wherein the Group III nitride layer has one or more properties selected from the group consisting of,
(i) lattice-matched to the epitaxial buffer layer; and
(ii) comprising a compound selected from the group consisting of GaN, AlGaN, InGaN, AlInGaN, AN, InN, SiCAlN, and mixtures thereof.
12. The method of claim 9 , wherein the substrate comprises Si, Al 2 O 3 , SiC or GaAs.
13. The method of claim 9 wherein the substrate comprises Si(111) or Si(100).
14. The method of claim 9 wherein the substrate comprises a miscut Si(111) substrate.
15. The method of claim 1 , wherein the precursor gas comprises (i) greater than about 98% v/v hydrogen and (ii) about 0.1-2 v/v % of a precursor source.
16. The method of claim 15 , wherein the temperature ranges from about 850° C. to about 950° C.
17. The method of claim 16 , wherein the epitaxial buffer layer has a thickness of greater than about 200 nm.
18. The method of claim 16 , wherein the epitaxial buffer layer has a thickness of greater than about 400 nm.