Single crystal group III nitride articles and method of producing same by HVPE method incorporating a polycrystalline layer for yield enhancement
In a method for making a GaN article, an epitaxial nitride layer is deposited on a single-crystal substrate. A 3D nucleation GaN layer is grown on the epitaxial nitride layer by HVPE under a substantially 3D growth mode. A GaN transitional layer is grown on the 3D nucleation layer by HVPE under a condition that changes the growth mode from the substantially 3D growth mode to a substantially 2D growth mode. A bulk GaN layer is grown on the transitional layer by HVPE under the substantially 2D growth mode. A polycrystalline GaN layer is grown on the bulk GaN layer to form a GaN/substrate bi-layer. The GaN/substrate bi-layer may be cooled from the growth temperature to an ambient temperature, wherein GaN material cracks laterally and separates from the substrate, forming a free-standing article.
1. A method of forming a semiconductor structure, the method comprising:
forming, over a substrate, a single-crystalline layer comprising a first III-nitride semiconductor material; and
forming, over the single-crystalline layer, a polycrystalline layer comprising a second III-nitride semiconductor material, thereby forming the semiconductor structure.
2. The method of claim 1 , wherein the first III-nitride semiconductor material and the second III-nitride semiconductor material are the same.
3. The method of claim 1 , wherein the substrate is selected from the group consisting of sapphire, silicon carbide, gallium arsenide, zinc oxide, silicon, spinel, lithium gallate, and lithium aluminate.
4. The method of claim 1 , further comprising, prior to forming the single-crystalline layer, forming an epitaxial nitride layer over the substrate.
5. The method of claim 4 , wherein the epitaxial nitride layer comprises a material selected from the group consisting of GaN, AlN, InN, and ternary and quaternary alloys and mixtures including one or more thereof.
6. The method of claim 4 , wherein forming the epitaxial nitride layer comprises sputtering.
7. The method of claim 1 , wherein forming the single-crystalline layer comprises:
forming a nucleation layer over the substrate under a substantially three-dimensional growth mode; and
forming a bulk layer over the nucleation layer under a substantially two-dimensional growth mode.
8. The method of claim 7 , wherein the nucleation layer and the bulk layer each comprise a material selected from the group consisting of GaN, AlN, InN, and ternary and quaternary alloys and mixtures including one or more thereof.
9. The method of claim 7 , wherein forming the single-crystalline layer comprises forming, between the nucleation layer and the bulk layer, a transitional layer under a growth mode that changes from the substantially three-dimensional growth mode to the substantially two-dimensional growth mode.
10. The method of claim 9 , wherein the transitional layer comprises a material selected from the group consisting of GaN, AlN, InN, and ternary and quaternary alloys and mixtures including one or more thereof.
11. The method of claim 1 , wherein the second III-nitride semiconductor material comprises a material selected from the group consisting of GaN, AlN, InN, and ternary and quaternary alloys and mixtures including one or more thereof.
12. The method of claim 1 , wherein forming the single-crystalline layer comprises doping with at least one of an n-type dopant, a p-type dopant, or a deep-level acceptor.
13. The method of claim 1 , wherein the polycrystalline layer is formed at an elevated temperature greater than approximately 850° C., and further comprising cooling the semiconductor structure from the elevated temperature.
14. The method of claim 13 , wherein the substrate separates from at least a portion of the single-crystalline layer during cooling.
15. The method of claim 13 , wherein the semiconductor structure is cooled at a rate less than approximately 20° C. per minute.
16. The method of claim 1 , further comprising removing the polycrystalline layer from the single-crystalline layer.
17. The method of claim 16 , wherein removing the polycrystalline layer comprises at least one of grinding, lapping, or polishing.
18. The method of claim 16 , further comprising processing the single-crystalline layer by at least one of planarization, polishing, chemical-mechanical polishing, grinding or lapping.