A seed substrate for epitaxial growth has a support substrate, a planarizing layer of 0.5 to 3 ?m provided on the top surface of the support substrate, and a seed crystal layer provided on the top surface of the planarizing layer. The support substrate includes a core of group III nitride polycrystalline ceramics and a 0.05 to 1.5 ?m encapsulating layer that encapsulates the core. The seed crystal layer is provided by thin-film transfer of 0.1 to 1.5 ?m of the surface layer of Si<111> single crystal with oxidation-induced stacking faults (OSF) of 10 defects/cm.sup.2 or less. High-quality, inexpensive seed substrates with few crystal defects for epitaxial growth of epitaxial substrates and solid substrates of group III nitrides such as AlN, AlxGa1-xN (0<X<1) and GaN are obtained.

A seed substrate for epitaxial growth has a support substrate, a planarizing layer of 0.5 to 3 ?m provided on the top surface of the support substrate, and a seed crystal layer provided on the top surface of the planarizing layer. The support substrate includes a core of group III nitride polycrystalline ceramics and a 0.05 to 1.5 ?m encapsulating layer that encapsulates the core. The seed crystal layer is provided by thin-film transfer of 0.1 to 1.5 ?m of the surface layer of Si<111> single crystal with oxidation-induced stacking faults (OSF) of 10 defects/cm.sup.2 or less. High-quality, inexpensive seed substrates with few crystal defects for epitaxial growth of epitaxial substrates and solid substrates of group III nitrides such as AlN, AlxGa1-xN (0<X<1) and GaN are obtained.

A method for manufacturing a semiconductor device includes epitaxially growing a carrier-transport layer of a first conductivity type on a substrate of silicon carbide; irradiating the carrier-transport layer with a first light having a wavelength equal to or less than an absorption-edge wavelength of silicon carbide at a temperature of less than 400 degrees Celsius so as to expand a stacking fault originating from a basal plane dislocation which are propagated from the substrate to the carrier-transport layer; heating the carrier-transport layer in which the stacking fault has expanded so as to shrink the stacking fault, at a shrinking temperature of 400 degrees Celsius or more and 1000 degrees Celsius or less; and forming a carrier-injection region of a second conductivity type on the carrier-transport layer, the carrier-injection region injects carriers into the carrier-transport layer.

A method for manufacturing a semiconductor device includes epitaxially growing a carrier-transport layer of a first conductivity type on a substrate of silicon carbide; irradiating the carrier-transport layer with a first light having a wavelength equal to or less than an absorption-edge wavelength of silicon carbide at a temperature of less than 400 degrees Celsius so as to expand a stacking fault originating from a basal plane dislocation which are propagated from the substrate to the carrier-transport layer; heating the carrier-transport layer in which the stacking fault has expanded so as to shrink the stacking fault, at a shrinking temperature of 400 degrees Celsius or more and 1000 degrees Celsius or less; and forming a carrier-injection region of a second conductivity type on the carrier-transport layer, the carrier-injection region injects carriers into the carrier-transport layer.

A method of planarizing a roughened surface of a SiC substrate includes: forming a sacrificial material on the roughened surface of the SiC substrate, the sacrificial material having a density between 35% and 120% of the density of the SiC substrate; implanting ions through the sacrificial material and into the roughened surface of the SiC substrate to form an amorphous region in the SiC substrate; and removing the sacrificial material and the amorphous region of the SiC substrate by wet etching.

A method of planarizing a roughened surface of a SiC substrate includes: forming a sacrificial material on the roughened surface of the SiC substrate, the sacrificial material having a density between 35% and 120% of the density of the SiC substrate; implanting ions through the sacrificial material and into the roughened surface of the SiC substrate to form an amorphous region in the SiC substrate; and removing the sacrificial material and the amorphous region of the SiC substrate by wet etching.

A wavelength conversion element manufacturing method capable of realizing, in a wavelength conversion element having a structure in which a thin film substrate having a periodic polarization inversion structure and a support substrate are laminated, highly efficient wavelength conversion by confining light in a cross-sectional area smaller than in the known art. The manufacturing method includes steps of forming a periodic polarization inversion structure on a first substrate made of a second-order nonlinear optical crystal and forming a damage layer in the first substrate by implanting ions from one substrate surface to obtain a first substrate for bonding, directly bonding a second substrate having a bonding surface having a smaller refractive index than the first substrate to the one substrate surface of the first substrate at the bonding surface, and peeling the first substrate directly bonded to the second substrate being the support substrate with the damage layer as a boundary to remove a part of the first substrate.

A wavelength conversion element manufacturing method capable of realizing, in a wavelength conversion element having a structure in which a thin film substrate having a periodic polarization inversion structure and a support substrate are laminated, highly efficient wavelength conversion by confining light in a cross-sectional area smaller than in the known art. The manufacturing method includes steps of forming a periodic polarization inversion structure on a first substrate made of a second-order nonlinear optical crystal and forming a damage layer in the first substrate by implanting ions from one substrate surface to obtain a first substrate for bonding, directly bonding a second substrate having a bonding surface having a smaller refractive index than the first substrate to the one substrate surface of the first substrate at the bonding surface, and peeling the first substrate directly bonded to the second substrate being the support substrate with the damage layer as a boundary to remove a part of the first substrate.

A method for producing a diamond single crystal includes implanting an ion other than carbon into a surface of a diamond single crystal seed substrate and thereby decreasing the transmittance of light having a wavelength of 800 nm, the surface having an off-angle of 7 degrees or less with respect to a {100} plane, and homoepitaxially growing a diamond single crystal on the ion-implanted surface of the seed substrate using a chemical vapor synthesis under synthesis conditions where the ratio N.sub.C/N.sub.H of the number of carbon-containing molecules N.sub.C to the number of hydrogen molecules N.sub.H in a gas phase is 10% or more and 40% or less, the ratio N.sub.N/N.sub.C of the number of nitrogen molecules N.sub.N to the number of carbon-containing molecules N.sub.C in the gas phase is 0.1% or more and 10% or less, and the seed substrate temperature T is 850 C. or more and less than 1000 C.

A method for producing a diamond single crystal includes implanting an ion other than carbon into a surface of a diamond single crystal seed substrate and thereby decreasing the transmittance of light having a wavelength of 800 nm, the surface having an off-angle of 7 degrees or less with respect to a {100} plane, and homoepitaxially growing a diamond single crystal on the ion-implanted surface of the seed substrate using a chemical vapor synthesis under synthesis conditions where the ratio N.sub.C/N.sub.H of the number of carbon-containing molecules N.sub.C to the number of hydrogen molecules N.sub.H in a gas phase is 10% or more and 40% or less, the ratio N.sub.N/N.sub.C of the number of nitrogen molecules N.sub.N to the number of carbon-containing molecules N.sub.C in the gas phase is 0.1% or more and 10% or less, and the seed substrate temperature T is 850 C. or more and less than 1000 C.