Study of argon-irradiation-induced defects and amorphization in silicon using a positron beam, Raman spectroscopy and ion channelling

Abstract

Studies of irradiation-induced defects have been carried out on silicon single-crystal samples, irradiated with 140 keV argon ions to doses in the range 5 × 1014 to 5 × 1016 cm-2, using a variable-low-energy positron beam, Raman spectroscopy and ion channelling. The Doppler broadening lineshape S-parameter has been found to exhibit a peak as a function of the positron beam energy Ep and a subsequent saturation behaviour for all irradiated samples. The peak damage occurs at a depth of 100 nm, consistent with TRIM code calculations. The measured S-Ep curves are analysed using a positron diffusion model to obtain the depth profile of positron-trapping defects. The behaviour of the S-W correlation plots and the variation of the R-parameter indicate that the nature of the open-volume defects is independent of the dose and the dominant defects are vacancy clusters larger than divacancies. Raman spectroscopic studies indicate that all of the irradiated samples are amorphized, and the degree of residual crystallinity across the irradiated zone of the sample is obtained. Ion-channelling studies carried out on the samples have yielded thicknesses of the amorphized layer which are consistent with positron beam results. In contrast to the TRIM code calculations, the present results show the presence of defects at depths far beyond the Ar-ion range. The results of the positron beam, Raman and ion-channelling studies are discussed in the context of ion-induced defects and amorphization.