Lattice Disorder in Br, Cl, and F Implanted CdS — Channeling Study

Abstract

Backscattering of 2 MeV He⁺ has been used to examine lattice disorder production and annealing of CdS implanted with keV Br, Cl, and F at fluences ranging between 1 × 10¹⁴ cm^-2 to 1 × 10¹⁷ cm^-2. Using a calculated value of 60 eV/Å for the dE/dx of 1.80 MeV He⁺ in CdS, the measured depths of the disorder peaks are 82 Å, 144 Å, and 422 Å, respectively. The measured depths of the Cl and Br disorder peaks are only 42% as deep as their calculated projected ranges, whereas the measured F peak is 71% as deep as that calculated. For each ion species, the number of scattering centers produced increased linearly with log fluence, and for Br a satxiration value of 2.4 × 10¹⁶ atoms/cm² was reached. The Cl implants approach a saturation greater than 5.3 × 10¹⁶ atoms/cm², and no saturation was observed for the F implants. The rates at which Cd atoms are displaced from the lattice are 10 atoms/Br ion, 3 atoms/Cl ion, and 2.5 atoms/F ion. The backscattering spectra do not indicate amorphous layer formation for the saturation Br implants, but do indicate this for the 8 × 10¹⁶ Cl/cm² and the 1 × 10¹⁷ F/cm² implants. The saturation fluence for Br appears consistent with qualitative electron microscopy results for Ag implants in CdS which indicate fluences greater than 1 x× 10¹⁵ Ag/ cm² are required to produce overlapping of discrete disorder clusters observed at lower fluences.

Isochronal anneal studies performed up to 500° C show that a significant amount of disorder is removed between 200° C and 300° C for the F and Cl implants, whereas disorder annealing is found approximately between 100° C and 250° C and between 400° C and 500° C in the Br implanted samples. Reverse annealing was observed for the F and Cl implants in the temperature range 25° C to 200° C. For Br implants, the reverse annealing peaked at 100° C. Previous studies of fast neutron irradiation effects in CdS reveal an anneal stage between room temperature and 300° C. Also, electron microscopy of Ag implants reveal an annealing stage above 400° C, These results tentatively suggest similar defects are present in the neutron, F, and Cl implants and that an additional defect is present in the Ag and Br implants.