Revealing Raman Spectral Parameters’ Sensitivity Hierarchy toward Fano Resonance in a Semiconductor

Abstract

Fano resonance is known to affect the Raman line shape through changes in its width, peak position, and the induction of an antiresonance dip, which varies with the Fano coupling strength. In this connection, it has remained an inquisitive question to identify which, out of width, peak shift, and antiresonance, starts responding first when Fano resonance is present in a solid. The sensitivity of the Fano coupling parameter to the Raman parameter has been investigated here analytically, followed by its experimental verification. The latter has been carried out through Raman scattering experiments on degenerate silicon (Si), where the Fano effect is inherently present because of doping. The coupling strength has been varied through two routes, namely excitation wavelength and doping concentration. The evolution of the red shift of the resonance maximum with the increase in Fano coupling strength, due to rising boron concentration, reveals a distinctly different behavior when compared to the usual Fano-dependent Raman behavior. Furthermore, the theoretical analysis confirms its connection with the weakening of the lattice-restoring force. However, the phonon energy remains invariant with wavelength, while the blue shift is attributed to changes in the electronic continuum of Si with excitation wavelength. Additionally, the present study shows that the Fano interaction remains identifiable even when the antiresonance dip or visible asymmetry is weak, by comparing the Raman line-shaped width in regimes where Fano coupling is effectively weak or absent. These findings offer profound insights into the electronic and vibrational correlations of semiconducting materials. © 2026 American Chemical Society