ScAlMgO4 monocrystalline substrate, and method of manufacture thereof

1. A stacked structure comprising

a ScAlMgO 4 monocrystalline substrate, and

a GaN film on a principal surface of the ScAlMgO 4 monocrystalline substrate,

wherein the ScAlMgO 4 monocrystalline substrate has a crystal oxygen concentration of 57 atom % or less and 56 atom % or greater as measured by inductively coupled plasma atomic emission spectroscopy analysis,

wherein the ScAlMgO 4 monocrystalline substrate has a curvature radius R and a thickness t s satisfying 5.0 N/mm 2 ≤σ in the following formula:

σ=( E f ×t f 2 )×10 3 /(6×(1− v f )× R×t s ),

wherein E f represents the Young's modulus of the GaN film,

wherein v f represents the Poisson's ratio of the GaN film, and

wherein t f represents the thickness of the GaN film,

wherein the thickness (t s ) of the ScAlMgO 4 monocrystalline substrate is 300 μm to 400 μm, and

wherein the thickness (t s ) of the GaN film is 1 mm to 1.5 mm.

2. The stacked structure according to claim 1 ,

wherein the ScAlMgO 4 monocrystalline substrate is manufactured by a method comprising:

a seeding step of contacting a seed crystal to a melt of a feedstock of a monocrystalline substrate represented by ScAlMgO 4 to generate a crystal; and

a crystal growth step of growing a single crystal by pulling the crystal generated in the seeding step,

wherein, in the crystal growth step, the crystal is pulled from the melt in an atmosphere having an oxygen concentration of 0.1 volume % or less, and

wherein, in the crystal growth step, the melt has a temperature gradient of 4.4° C/mm or more immediately below its liquid level.