Lattice Disorder in Br, Cl, and F Implanted CdS — Channeling Study
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.
KeywordsAmorphous Layer Annealing Stage Lattice Disorder Saturation Fluence Random Spectrum
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