Abstract: There is provided a novel method for producing a nitride single crystal with both a rapid crystal growth rate and high crystal quality, as well as a novel autoclave that can be used in the method. The invention provides a method for producing a Ga-containing nitride single crystal by an ammonothermal method, comprising introducing at least a starting material, an acidic mineralizer and ammonia into an autoclave, and then growing a Ga-containing nitride single crystal under conditions wherein the temperature (T1) at the single crystal growth site is 600° C. to 850° C., the temperature (T1) at the single crystal growth site and the temperature (T2) at the starting material feeder site are in the relationship T1>T2, and the pressure in the autoclave is 40 MPa to 250 MPa, as well as an autoclave that can be used in the method.

Abstract: An aluminum nitride single-crystal multi-layered substrate comprising an aluminum nitride single-crystal layer formed by direct reduction nitridation on a single-crystal ?-alumina substrate such as a sapphire substrate and an edge-type dislocation layer having a thickness of 10 nm or less in the vicinity of the interface between the both crystals. Threading dislocation is rarely existent in the aluminum nitride single-crystal layer existent on the surface. It is useful as a semiconductor device substrate.

Abstract: An aluminum nitride single-crystal multi-layered substrate comprising an aluminum nitride single-crystal layer formed by direct reduction nitridation on a single-crystal ?-alumina substrate such as a sapphire substrate and an edge-type dislocation layer having a thickness of 10 nm or less in the vicinity of the interface between the both crystals. Threading dislocation is rarely existent in the aluminum nitride single-crystal layer existent on the surface. It is useful as a semiconductor device substrate.