The number of Cu atoms in the 1.014eV Cu center in crystalline samples was deduced from the relationship between the photoluminescence intensity of the center and the Cu concentration in the sample. At Cu concentrations below about 1014/cm3, the photoluminescence intensity increased linearly with increasing Cu concentration. From this observation, and the law of mass action, it was concluded that the Cu center contained only one Cu atom; thus contradicting the long-held pair-model. A structural model in which the Cu atom was bonded to the center of the Si-Si bond was proposed here for the center.

Number of Cu atoms in the 1.014eV photoluminescence copper center in silicon M.Nakamura, S.Ishiwari, A.Tanaka: Applied Physics Letters, 1998, 73[16], 2325-7