Although the report is concerning a content with regard to a laminated layer structure, since the structure shown by FIGS. 1A, 1B and 1C is a structure where a SixGe1???x layer is sandwiched by Si layers and therefore, as shown by the schematic diagram of FIG. 2, a band gap (Eg2) of the SixGe1???x region is smaller than a band gap (Eg1) of the Si region.