of a crystal substrate having no epitaxial crystal grown thereon and containing boron of 4 u00d7 10 14 atoms cm 3 denoted by b c and d in fig2 are the spectra of three specimens wherein an epitaxial crystal of a thickness of 2 5 u03bcm was grown on the aforesaid crystal substrate phosphorus being added as an impurity thereto at the concentration of 1 6 u00d7 10 15 4 u00d7 15 15 and 1 5 u00d7 10 16 atoms cm 3 the peaks of these spectra are indicated by the atomic symbol of the impurity which caused the luminescence it is to be noted that the peak indicated by si is the luminescence inherent in silicon not due to impurities the patterns of the luminescent components caused by boron in the spectra b c and d are exactly the same as that of the spectrum a of the crystal substrate and are understood to be from the substrate also the luminescent components caused by phosphorus appearing in spectra b c and d have intensities which increase as the concentration of phosphorus increases here the result obtained by examining the relationship between the intensity ratio between the luminescent component 7 caused by boron in the substrate and the luminescent component 8 caused by phosphorus in the epitaxial crystal and the phosphorus concentration is given in fig3 as shown in fig3 there is a fixed relation.