Method and apparatus for producing large, single-crystals of aluminum nitride
Bulk single crystals of AlN having a diameter greater than about 25 mm and dislocation densities of about 10,000 cm −2 or less and high-quality AlN substrates having surfaces of any desired crystallographic orientation fabricated from these bulk crystals.
1. A semiconductor structure comprising:
an aluminum nitride single-crystal substrate having a diameter greater than 25 mm and a surface substantially all of which has a single crystalline orientation; and
an epitaxial layer disposed thereover, the epitaxial layer having an average dislocation density less than about 10,000 cm −2 .
2. The semiconductor structure of claim 1 , wherein the epitaxial layer comprises aluminum nitride.
3. The semiconductor structure of claim 1 , wherein the average dislocation density is less than about 5,000 cm −2 .
4. The semiconductor structure of claim 1 , wherein the average dislocation density is less than about 1,000 cm −2 .
5. The semiconductor structure of claim 1 , wherein the average dislocation density is less than about 500 cm −2 .
6. The semiconductor structure of claim 1 , wherein the average dislocation density is less than about 100 cm −2 .
7. The semiconductor structure of claim 1 having at least one region substantially devoid of dislocation defects, the at least one region having an area exceeding 25 mm.
8. The semiconductor structure of claim 1 , wherein the crystallographic orientation is selected from the group consisting of: {0001}, {10 1 0} and {11 2 0}.
9. The semiconductor structure of claim 1 , wherein the epitaxial layer comprises a material selected from the group consisting of AlN, GaN, InN, and any binary or tertiary alloy combination thereof.
10. The semiconductor structure of claim 1 , wherein the epitaxial layer is pseudomorphic and comprises GaN or AlGaN, an interface between the substrate and the epitaxial layer being substantially free of misfit dislocations.
11. The semiconductor structure of claim 10 , wherein the epitaxial layer comprises GaN, further comprising a pseudomorphic AlGaN layer disposed over the epitaxial layer, an interface between the epitaxial layer and the AlGaN layer being substantially free of misfit dislocations.
12. The semiconductor structure of claim 11 , wherein an Al concentration of the AlGaN layer is 50% or greater.
13. The semiconductor structure of claim 10 , further comprising an aluminum nitride layer disposed over the epitaxial layer.
14. The semiconductor structure of claim 1 , wherein a top surface of the substrate is non-polar, the epitaxial layer being disposed thereover.
15. The semiconductor structure of claim 1 , wherein a top surface of the substrate is polar, the epitaxial layer being disposed thereover and comprising polarization charge therewithin.
16. The semiconductor structure of claim 1 , further comprising a homoepitaxial aluminum nitride layer disposed between the substrate and the epitaxial layer.