Raman scattering from a p(+)-type porous silicon layer

A Raman scattering investigation has been performed on a p(+)-type porous silicon layer using both 488.0 and 514.5 nm Ar+ laser excitations. The Raman spectrum collected using 488.0 nm light exhibits an asymmetrically broadened peak with a lower Raman shift (Delta omega = 514.5 cm(-1)) than that for crystalline silicon (Delta omega = 520.5 cm(-1)) while the 514.5 nm spectrum consists of a sharp peak located at a Raman shift of 521 cm(-1) and a second broad peak at a shift of 517.6 cm(-1). The sharp peak in this spectrum is due to the presence of an Ar+ plasma line at 528.7 nm, which is a coincidence that seems to have gone unnoticed in the literature. The broad asymmetric component of the Raman spectrum excited with 514.5 nm light has a narrower linewidth and larger Raman shift than the corresponding peak in the 488.0 nm spectrum. This suggests that the nanocrystallite size increases with depth.