High-fluence implantations of silicon: Layer thickness and refractive indices

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Abstract
Refractive-index measurements are given for amorphous Si produced by ion implantation. Reflection interference measurements in the frequency range 250≲ν≲ 7600 cm−1 were made for several Si samples implanted with P-ion fluences between 1.0×1016 and 10×1016 ions/cm2 and ion energies between 0.20 and 2.7 MeV and for Si implants of 1.0×1016 and 3.0×1016 ions/cm2 and an ion energy of 0.30 MeV. The interference measurements were computer analyzed by using a model in which the damaged layer has a refractive index nD and extinction coefficient kD, and the substrate has a refractive index ns and ks=0. The optical constants of the two regions are smoothly connected by a transition region approximated by a half-Gaussian curve of standard deviation σD. The finite-width transition region is necessary for fitting the data. Excellent fits are obtained for literature values of ns and kD with the chi-square being ?10−5. The value of kD has little effect on the analysis. Within the experimental accuracy a single curve for nD(ν) is obtained for the amorphous region where nD(ν) is independent of the ion type, ion energy, ion fluence, or position in the amorphous layer. The thicknesses of the damaged layers deduced from the infrared data agree well with LSS values for Rp+σp and with channeling results. Visual observations of the thicknesses also agree well for the high-energy implants but not for the lower-energy ones.

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