Abstract: An object of the present invention is to provide a GaN crystal long in light emission lifetime by time-resolved photoluminescence measurement and provide high-quality GaN crystal and GaN substrate that have few specified crystal defects affecting the light emission lifetime. A gallium nitride crystal having a light emission lifetime by time-resolved photoluminescence measurement, of 5 ps or more and 200 ps or less, and satisfying at least one of the following requirement (i) and requirement (ii): (i) an FWHM in a 004 diffraction X-ray rocking curve is 50 arcsec or less at least one position of the crystal; and (ii) a dislocation density is 5×106 cm?2 or less.

Abstract: A pressure container for crystal production having excellent corrosion-resistance is provided. This pressure container produces crystals within the container using a seed crystal, a mineralizer, a raw material, and ammonia in a supercritical state or a subcritical state as a solvent. The pressure container has Ag present over the entire surface of at least the inner surface thereof in contact with the solvent. The Ag can be disposed by one or a combination of two or more among, for instance, Ag lining, Ag welding, and Ag plating. The mineralizer is preferably a fluorine mineralizer containing no halogen atoms other than fluorine.

Abstract: The present invention relates to a pressure container for crystal production having excellent corrosion-resistance. This pressure container produces crystals within the container using a seed crystal, a mineralizer, a raw material, and ammonia in a super critical state and/or a sub-critical state as a solvent. The pressure container has Ag present over the entire surface of at least the exposed inner surface thereof. The Ag can be disposed by one or a combination of two or more among, for instance, Ag lining, Ag welding, and Ag plating. The mineralizer is preferably a fluorine mineralizer containing no halogen atoms other than fluorine.

Abstract: To grow a highly pure nitride crystal having a low oxygen concentration efficiently by an ammonothermal method. A process for producing a nitride crystal, which comprises bringing a reactant gas reactive with ammonia to form a mineralizer, and ammonia into contact with each other to prepare a mineralizer in a reactor or in a closed circuit connected to a reactor; and growing a nitride crystal by an ammonothermal method in the presence of the ammonia and the mineralizer.

Abstract: A first object of the present invention is to provide a method for efficiently growing a nitride single crystal even under low pressure conditions. The present invention relates to a method for producing a nitride single crystal, comprising growing a nitride crystal on the surface of a seed crystal having a hexagonal crystal structure by setting a pressure in a reaction vessel having the seed crystal, a nitrogen-containing solvent, a mineralizer containing a fluorine atom, and a raw material placed therein to 5 to 200 MPa and performing control so that the nitrogen-containing solvent is in at least either a supercritical state or a subcritical state.

Abstract: To provide a production method for a nitride crystal, where a nitride crystal can be prevented from precipitating in a portion other than on a seed crystal and the production efficiency of a gallium nitride single crystal grown on the seed crystal can be enhanced. In a method for producing a nitride crystal by an ammonothermal method in a vessel containing a mineralizer-containing solution, out of the surfaces of said vessel and a member provided in said vessel, at least a part of the portion coming into contact with said solution is constituted by a metal or alloy containing one or more atoms selected from the group consisting of tantalum (Ta), tungsten (W) and titanium (Ti), and has a surface roughness (Ra) of less than 1.80 ?m.

Abstract: To provide a production method for a nitride crystal, where a nitride crystal can be prevented from precipitating in a portion other than on a seed crystal and the production efficiency of a gallium nitride single crystal grown on the seed crystal can be enhanced. In a method for producing a nitride crystal by an ammonothermal method in a vessel containing a mineralizer-containing solution, out of the surfaces of said vessel and a member provided in said vessel, at least a part of the portion coming into contact with said solution is constituted by a metal or alloy containing one or more atoms selected from the group consisting of tantalum (Ta), tungsten (W) and titanium (Ti), and has a surface roughness (Ra) of less than 1.80 ?m.

Abstract: To grow a highly pure nitride crystal having a low oxygen concentration efficiently by an ammonothermal method. A process for producing a nitride crystal, which comprises bringing a reactant gas reactive with ammonia to form a mineralizer, and ammonia into contact with each other to prepare a mineralizer in a reactor or in a closed circuit connected to a reactor; and growing a nitride crystal by an ammonothermal method in the presence of the ammonia and the mineralizer.

Abstract: The present invention provides low alloy steels having high strength and toughness, excellent high temperature creep rupture strength and ductility and low sensitivity to temper embrittlement. The alloy steel is a low carbon, low silicon-type Cr-Mo-V low alloy steel, to which are added aluminum, titanium, niobium and Zirconium individually or in combination and further, a small amount of boron.