Raman study of Fano interference in p-type doped silicon

As the silicon industry continues to push the limits of device dimensions,tools such as Raman spectroscopy are ideal to analyze and characterize the dopedsilicon channels. The effect of inter-valence band transitions on the zonecenter optical phonon in heavily p-type doped silicon is studied by Ramanspectroscopy for a wide range of excitation wavelengths extending from the red(632.8 nm) into the ultra-violet (325 nm). The asymmetry in the one-phonon Ramanlineshape is attributed to a Fano interference involving the overlap of acontinuum of electronic excitations with a discrete phonon state. We identify atransition above and below the one-dimensional critical point(EaΓ₁ = 3.4 eV) in the electronic excitation spectrum ofsilicon. The relationship between the anisotropic silicon band structure and thepenetration depth is discussed in the context of possible device applications.