ALUMINA SUBSTRATE

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Provided is an alumina substrate on which an AlN layer is formed and that causes less warping. Also provided is a substrate material that has a level of strength enabling it to withstand normal handling when an AlN crystal or the like is grown on the substrate, and that prevents cracking and fracturing of a grown crystal when excessive stress is applied thereto during growing or cooling. The substrate is an alumina substrate having an AlN layer formed on the surface, and having a gap and a rare earth element-containing region inside the AlN layer or at the interface between the AlN layer and the alumina substrate. Warping of the AlN layer can be reduced as a result of lattice-mismatch stress being concentrated at the rare earth element-containing region and releasing of stress by the gap. In addition, the rare earth element-containing region having a concentrating of stress, and the gap having a low mechanical strength, can induce initiation and propagation of cracks and fractures. As a result, contamination of cracks and fractures into the crystal grown on the substrate can be prevented. Furthermore, the rare earth element-containing region can ensure a level of mechanical strength sufficient for handling.