Nitride semiconductor substrate, semiconductor element, and method for manufacturing nitride semiconductor substrate

A nitride semiconductor substrate comprising:

• a substrate;
• and
• an AlN-containing film provided above the substrate,
• wherein a thickness of the AlN-containing film is at most 10000 nm,
• a threading dislocation density of the AlN-containing film is at most 1.5×108 cm−2,
• a full width at half maximum of an X-ray diffraction rocking curve of a (10-12) plane of the AlN-containing film is at most 120 arcsec,
• the substrate comprises one of sapphire, silicon carbide, or ScAlMgO4, and
• the AlN-containing film comprises:
• a first AlN film provided above the substrate;
• and
• a second AlN film provided above the first AlN film;
• wherein a thickness of the first AlN film is at least 100 nm and at most 900 nm,
• a thickness of the second AlN film is at least 100 nm and at most 900 nm, and
• the second AlN film comprises AlxGayIn1-x-yN, wherein 0.5≤x≤1, 0≤y≤0.5, and x+y≤1.