Aluminum nitride plate

An aluminum nitride plate, wherein

• the aluminum nitride plate satisfies following relations (1) to (4)
• c1>97.5%, (1):
• c2>97.0%, (2):
• w1<2.5 degrees, (3):
• w1/w2<0.996 (4):
• where c1 is a c-plane degree of orientation that is defined as a ratio of a diffraction intensity of (002) plane to a sum of the diffraction intensity of (002) plane and a diffraction intensity of (100) plane when a surface layer of the aluminum nitride plate is subjected to an X-ray diffraction measurement along a thickness direction of the surface layer, and
• c2 is a c-plane degree of orientation that is defined as a ratio of the diffraction intensity of (002) plane to the sum of the diffraction intensity of (002) plane and the diffraction intensity of (100) plane when a portion other than the surface layer of the aluminum nitride plate is subjected to the X-ray diffraction measurement along a thickness direction of the portion other than the surface layer, wherein w1 is a half-value width in an X-ray rocking curve profile of (102) plane of the surface layer of the aluminum nitride plate and w2 is a half-value width in the X-ray rocking curve profile of (102) plane of the portion other than the surface layer of the aluminum nitride plate.