Lattice Disorder in Br, Cl, and F Implanted CdS — Optical Reflection Study
Optical reflection spectra (3.45 to 5.90 eV) are presented for CdS implanted with 40 keV Br, Cl, and F at fluences between 1 × 1014 and 1 × 1017 cm-2 and followed by isochronal anneals up to 500° C. Two reflection peaks located at 0.252 μm (E1:A) and 0.226 μm (E1:B) present in crystalline CdS decrease with increasing fluence. The ratio (E1:A/E1:B = r) of the two peaks is ion species dependent. The Fl and Cl implants increase r with fluence, whereas for Br implants r remains constant. For each species, the fractional change of reflectivity (ΔR/Ri) of E1:A increases linearly with log fluence for fluences less than 3 × 1015 cm-2. However, for fluences larger than 7 × 1015 cm-2, ΔR/Ri saturates for Br implants, but increases superlinearly for Cl and F implants. Comparison with similar channeling measurements (CM) indicates that ΔR/Ri provides a more sensitive measurement of disorder for low fluences. For fluences above saturation levels found in CM, the correlation ranges from good for Br and F implants to poor for Cl implants. In the latter case, comparison is complicated by errors introduced into the measurement of Peak E1:A caused by variations of r between samples implanted with equal fluences. By causing fluctuations in peak overlap, these variations of r also produce fluctuations in Peak E1:A, and suggest the use of only isolated peaks in reflection spectroscopic analyses of lattice disorder.
Isochronal anneal studies performed up to 500° C show a significant amount of disorder is removed between 200° C and 500° C for the F and Cl implants and between 200° C and 300° C for the Br implants. Also, all implants show a definite reverse anneal stage for temperatures less than 200° C. The correlation between reflection measurements and CM anneal data is fair for F and Cl implants and poor for the Br implants.
KeywordsReflection Measurement Channel Measurement Reflection Peak Fractional Change Optical Reflection
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