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Large area seed crystals for ammonothermal GaN growth are fabricated by deposition or layer transfer of a GaN layer on a CTE-matched handle substrate. The sides and back of the handle substrate are protected from the ammonothermal growth environment by a coating comprising an adhesion layer, a diffu

Large area seed crystals for ammonothermal GaN growth are fabricated by deposition or layer transfer of a GaN layer on a CTE-matched handle substrate. The sides and back of the handle substrate are protected from the ammonothermal growth environment by a coating comprising an adhesion layer, a diffusion barrier layer, and an inert layer. A patterned mask, also comprising an adhesion layer, a diffusion barrier layer, and an inert layer, may be provided over the GaN layer to allow for reduction of the dislocation density by lateral epitaxial growth.

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1. A method for forming a free-standing ammonothermal group III metal nitride crystal, comprising: providing a non-gallium-nitride substrate having a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 4-8×10−6/K, averaged between room temperat

1. A method for forming a free-standing ammonothermal group III metal nitride crystal, comprising: providing a non-gallium-nitride substrate having a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 4-8×10−6/K, averaged between room temperature and 700 degrees Celsius;providing a crystalline gallium-containing nitride layer overlying the substrate;depositing a diffusion barrier layer and an inert layer overlying at least some side surfaces of the substrate and the diffusion barrier layer, the diffusion barrier layer comprising at least one of W, TiW, Ta, Mo, and Re, and the inert layer comprising at least one of Au, Ag, Pt, Pd, Rh, Ru, Ir, Re, Ni, Cr, V, Ti, and Ta;placing the substrate, a group III metal source, at least one mineralizer composition, and a nitrogen containing solvent within a sealable container; andforming an ammonothermal group III metal nitride crystal on the crystalline gallium-containing nitride layer by heating the sealable container to a temperature of at least about 400 degrees Celsius. 2. The method of claim 1, wherein providing the crystalline gallium-containing nitride layer comprises using a layer transfer process. 3. The method of claim 1, wherein providing the crystalline gallium-containing nitride layer comprises using epitaxial deposition. 4. The method of claim 1, wherein the non-gallium-nitride substrate comprises molybdenum. 5. The method of claim 1, wherein the non-gallium-nitride substrate comprises polycrystalline aluminum nitride. 6. The method of claim 1, wherein the non-gallium-nitride substrate comprises two outer substrates overlying an inner substrate and bonded by bonding layers forming a composite layer structure. 7. The method of claim 6, wherein the two outer substrates comprise silicon carbide and the at least one inner substrate comprises tantalum. 8. The method of claim 6, wherein the composite layer structure is brazed. 9. The method of claim 6, wherein a maximum principal stress in the composite layer structure is less than about 250 MPa. 10. The method of claim 1, further comprising depositing at least one patterned mask layer on the crystalline gallium-containing nitride layer to form a patterned substrate, wherein the patterned mask layer: comprises one or more of an adhesion layer, and an inert layer;comprises one or more of Au, Ag, Pt, Pd, Rh, Ru, Ir, Ni, Cr, V, Ti, or Ta;is characterized by a thickness between about 10 nanometers and about 100 micrometers; andcomprises a one-dimensional or two-dimensional array of openings, wherein the openings are characterized by an opening dimension between about 1 micrometer and about 5 millimeters and a pitch dimension between about 5 micrometers and about 20 millimeters. 11. The method of claim 10, wherein the patterned mask layer comprises a one-dimensional or two-dimensional array of openings, wherein the openings are characterized by an opening dimension between about 10 micrometers and about 500 micrometers and a pitch dimension between about 200 micrometers and about 5 millimeters. 12. The method of claim 1, further comprising removing the ammonothermally-grown group III metal nitride crystal from the substrate and processing the ammonothermally-grown group III metal nitride crystal to form a free-standing, ammonothermally-grown group III metal nitride crystal. 13. The method of claim 12, further comprising incorporating the free-standing ammonothermal group III metal nitride crystal into a semiconductor structure, the semiconductor structure comprising at least one AlxInyGa(1-x-y)N epitaxial layer, where 0≦x, y, x+y≦1. 14. The method of claim 13, further comprising incorporating the semiconductor structure into an electronic device or an optoelectronic device selected from a light emitting diode, a laser diode, a photodetector, an avalanche photodiode, a photovoltaic, a solar cell, a cell for photoelectrochemical splitting of water, a transistor, a rectifier, a thyristor, a transistor, a rectifier, a Schottky rectifier, a thyristor, a p-i-n diode, a metal-semiconductor-metal diode, high-electron mobility transistor, a metal semiconductor field effect transistor, a metal oxide field effect transistor, a power metal oxide semiconductor field effect transistor, a power metal insulator semiconductor field effect transistor, a bipolar junction transistor, a metal insulator field effect transistor, a heterojunction bipolar transistor, a power insulated gate bipolar transistor, a power vertical junction field effect transistor, a cascode switch, an inner sub-band emitter, a quantum well infrared photodetector, a quantum dot infrared photodetector, and a combination of any of the foregoing. 15. The method of claim 1, wherein the non-gallium-nitride substrate his characterized by a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 5-7×10−6/K, averaged between room temperature and 700 degrees Celsius. 16. The method of claim 1, wherein the non-gallium-nitride substrate is characterized by a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 5.5-6.5×10−6/K, averaged between room temperature and 700 degrees Celsius. 17. The method of claim 1, further comprising depositing an adhesion layer overlying at least the side surfaces of the substrate and underlying the diffusion barrier layer, the adhesion layer comprising at least one of Ti and Cr. 18. The method of claim 1, wherein the ammonothermal group III metal nitride layer formed on the substrate is characterized by a thickness of at least 500 micrometers. 19. A method for forming a free-standing ammonothermal group III metal nitride crystal, comprising: providing a non-gallium-nitride substrate characterized by a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 5.5-6.5×10−6/K, averaged between room temperature and 700 degrees Celsius;providing a crystalline gallium-containing nitride layer overlying the substrate;depositing at least one patterned mask layer on the crystalline gallium-containing nitride layer to form a patterned substrate, wherein the patterned mask layer: comprises one or more of an adhesion layer, a diffusion-barrier layer, and an inert layer;comprises one or more of Au, Ag, Pt, Pd, Rh, Ru, Ir, Ni, Cr, V, Ti, or Ta;is characterized by a thickness between about 10 nanometers and about 100 micrometers; andcomprises a one-dimensional or two-dimensional array of openings, wherein the openings are characterized by an opening dimension between about 1 micrometer and about 5 millimeters and a pitch dimension between about 5 micrometers and about 20 millimeters;depositing an inert layer overlying at least some side surfaces of the substrate, wherein the inert layer comprises at least one of Au, Ag, Pt, Pd, Rh, Ru, Ir, Re, Ni, Cr, V, Ti, and Ta;placing the substrate, a group III metal source, at least one mineralizer composition, and a nitrogen containing solvent within a sealable container;forming an ammonothermal group III metal nitride crystal characterized by a thickness of at least 500 micrometers by heating the sealable container to a temperature of at least about 400 degrees Celsius; andremoving an ammonothermally-grown group III metal nitride crystal from the substrate and processing ammonothermally-grown group III metal nitride crystal to form a free-standing, ammonothermally-grown group III metal nitride crystal. 20. A method for forming a free-standing ammonothermal group III metal nitride crystal, comprising: providing a non-gallium-nitride substrate characterized by a coefficient of thermal expansion approximately equal to that of gallium nitride, with a value in a range of 5.5-6.5×10−6/K, averaged between room temperature and 700 degrees Celsius, wherein the non-gallium-nitride substrate comprises a composite layer structure comprising a first large-area surface and a second large-area surface on an opposite side of the substrate from the first large-area surface;providing a crystalline gallium-containing nitride layer overlying each of the first large-area surface and the second large-area surface;depositing at least one patterned mask layer on each of the crystalline gallium-containing nitride layers to form a patterned substrate, wherein the patterned mask layer: comprises one or more of an adhesion layer, a diffusion-barrier layer, and an inert layer;comprises one or more of Au, Ag, Pt, Pd, Rh, Ru, Ir, Ni, Cr, V, Ti, or Ta;is characterized by a thickness between about 10 nanometers and about 100 micrometers; andcomprises a one-dimensional or two-dimensional array of openings, wherein the openings are characterized by an opening dimension between about 1 micrometer and about 5 millimeters and a pitch dimension between about 5 micrometers and about 20 millimeters;depositing an inert layer overlying at least some side surfaces of the substrate, wherein the inert layer comprises at least one of Au, Ag, Pt, Pd, Rh, Ru, Ir, Re, Ni, Cr, V, Ti, and Ta;placing the substrate, a group III metal source, at least one mineralizer composition, and a nitrogen containing solvent within a sealable container;forming an ammonothermal group III metal nitride crystal characterized by a thickness of at least 500 micrometers by heating the sealable container to a temperature of at least about 400 degrees Celsius; andremoving the ammonothermally-grown group III metal nitride crystal from the substrate and processing the ammonothermally-grown group III metal nitride crystal to form a free-standing, ammonothermally-grown group III metal nitride crystal.