Micro-Raman-scattering study of surface-related phonon modes in porous GaP

Porous GaP layers prepared by electrochemical dissolution of (100)-oriented bulk material have been studied by micro-Raman spectroscopy. The anodization causes a breakdown of the polarization selection rules, inherent to a (100) surface, accompanied by a downward shift of the LO-phonon frequency and by the appearance of a surface-related vibrational mode in the gap between the bulk optical phonons. The frequency of the surface-related mode was found to decrease from 398 to 394.3 ${\mathrm{cm}}^{\mathrm{-}1}$ with increasing anodization current. A Raman line-shape analysis based on the light scattering due to the electro-optic and deformation potential mechanisms is presented.