The present disclosure provides a composite substrate including: a support layer; and a SiC monocrystalline layer on the support layer, where the SiC monocrystalline layer includes a first superjunction structure that includes first P-type layers and first N-type layers, and the first P-type layers and the first N-type layers extend inward along a thickness direction of the SiC monocrystalline layer from a surface of the SiC monocrystalline layer far from the support layer, and are alternately distributed in a direction parallel to a plane of the SiC monocrystalline layer.