To fabricate a practically useful non-polar AlN buffer layer on a sapphire crystal plate and manufacture a UV light-emitting device on a non-polar crystal substrate by adopting the crystal substrate as an example, an embodiment of the present invention provides a crystal substrate 1D comprising an r-plane sapphire crystal plate 10 and an AlN buffer layer 20D of non-polar orientation. The AlN buffer layer comprises a surface protection layer 22 and a smoothing layer 26. The surface protection layer suppresses roughness increase on a surface of the AlN buffer layer, and the smoothing layer makes the surface of the AlN buffer layer a smoothed surface. Also provided is a crystal substrate 11 comprising an AlN buffer layer 20T to which a dislocation blocking layer 24 for reducing crystallographic defects is added between the surface protection layer 22 and the smoothing layer 26. In another embodiment a deep UV light-emitting device is provided.