A substrate 10 contains a first layer L1 and a second layer L2 that are stacked on one another, the first layer L1 contains crystalline AlN and an additive element, the second layer L2 contains crystalline α-alumina, the additive element is at least one selected from the group consisting of rare earth elements, alkaline earth elements, and alkali metal elements, the thickness of the first layer L1 is 5 to 600 nm, RC(002) is a rocking curve of diffracted X-rays originating from a (002) plane of AlN, RC(002) is measured by an ω-scan of the surface SL1 of the first layer L1, the half width of RC(002) is 0° to 0.4°, RC(100) is a rocking curve of diffracted X-rays originating from a (100) plane of AlN, RC(100) is measured by a ϕ-scan of the surface SL1 of the first layer L1, and the half width of RC(100) is 0° to 0.8°.