An epitaxial structure includes a first type semiconductor layer, an active layer, a second type semiconductor layer, and a lattice mismatch layer. The first type semiconductor layer includes a material of aluminum gallium indium phosphide. The active layer is disposed on a side of the first type semiconductor layer. The second semiconductor layer is disposed on a side of the active layer away from the first type semiconductor layer, and includes the material of aluminum gallium indium phosphide. The lattice mismatch layer includes the material of aluminum gallium indium phosphide and is disposed on any side of the first type semiconductor layer, the active layer, or the second type semiconductor layer. In an X-ray diffractometer analysis spectrum, at least one of the first type semiconductor layer, the active layer and the second type semiconductor layer corresponds to a main diffractive peak, the lattice mismatch layer has a secondary diffractive peak.