PHOTOLUMINESCENCE STUDY OF CADMIUM-RELATED DEFECTS IN OXYGEN-RICH SILICON

We report the results of a photoluminescence study of three Cd-related defects in Czochralski (CZ) silicon annealed at similar to 600 degree s C for 30 min, with zero phonon lines near 1026, 983, and 935 meV. Th e 983-meV defect has been previously reported, while the 1026- and 935 -meV defects are described here. Revised uniaxial stress results on th e 983-meV center give clear proof that the transition occurs at a site of rhombic I (C-2v) symmetry, and stress measurements on the 1026- an d 935 meV centers indicate rhombic I and monoclinic I (C-1h) symmetrie s, respectively. Preliminary Zeeman experiments show no shift or split ting for any of the lines reported, and this leads us to attribute the lines to recombination between a tightly-bound hole and loosely-bound electron at isoelectronic centers. Cadmium-isotope substitution exper iments give unambiguous proof of the involvement of one cadmium atom i n the three defects, and indicate that the local mode vibrations of th e defects are predominantly due to the motion of the cadmium atom alon e. These defects are seen only in CZ silicon, and this indicates that oxygen is likely to be involved in the defect formation, particularly as no evidence is seen for the involvement of other common impurities in CZ silicon such as carbon and hydrogen. Finally, we examine the sim ilarities and differences between these Cd-related defects and previou sly reported Zn-related defects.