Optical properties and surface damage studies of crystalline silicon caused by swift iron ions

Abstract

p-Type silicon samples irradiated with 70MeV 56Fe5+ ions for various fluences varying between 5×1012 and 4×1014ionscm−2 have been studied using spectroscopic ellipsometry and Fourier transform infrared spectroscopy. The microstructure of the irradiated samples was modeled from ellipsometric data, using a multilayer optical model and Bruggeman effective medium approximation. The values of pseudodielectric function, absorption coefficient and Penn gap energy were determined with respect to ion fluence. The effective medium analysis suggests that the superficial silicon layer can be explained as a mixture of crystalline and damaged silicon. The thickness of the damaged layer and percentage of voids present in the layer were found to increase with increase in the ion fluence. The effect of disorder on the interband optical spectra, especially on the critical point E1 at 3.4eV was found to vary with ion fluence. A red shift in the critical point E1 with increasing ion fluence was observed. FTIR study showed of silicon samples irradiated with 70MeV 56Fe5+ ions produced the oscillations in the spectral region 1000–400cm−1. As irradiated sample showed more pronounced fringes, while contrast of the fringes and amplitude both were found to decrease with increase in depth.