A photoluminescence study was made of Cd-related defects in annealed (600C, 0.5h) Czochralski material. This revealed zero phonon lines near to 1.026, 0.983 and 0.935eV. The 0.983eV defect had previously been reported, and attention was devoted here to the 1.026 and 0.935eV defects. Revised uniaxial stress data for the 0.983eV center furnished proof that the transition occurred at a site of rhombic I (C2v) symmetry. Stress measurements of the 1.026 and 0.935eV centers indicated rhombic and monoclinic (C1h) symmetries, respectively. Zeeman experiments revealed no shifts or splitting of any of the lines, and they were therefore attributed to recombination between a tightly-bound hole and a loosely bound electron at iso-electronic centers. The use of Cd isotope substitution furnished proof for the involvement of one Cd atom in the 3 defects, and indicated that local mode vibrations of the defects were due mainly to the motion of the Cd atom alone. These defects were seen only in Czochralski material; thus indicating that O was likely to be involved in the defect formation. There was no evidence for the involvement of other common impurities, such as C or H.

E.McGlynn, M.O.Henry, K.G.McGuigan, M.C.Do Carmo: Physical Review B, 1996, 54[20], 14494-503