Frohlich modes in porous III-V semiconductors

Porous GaP, InP and GaAs structures fabricated by MeV ion-implantation-assi sted electrochemical etching were investigated by Raman and Fourier transfo rm infrared spectroscopy. Frohlich modes in the frequency gap between the t ransverse optical and longitudinal optical frequencies were observed and th eir longitudinal-transverse splitting was established. The frequency-depend ent optical properties in the infrared region were calculated using a diele ctric function derived on the basis of an appropriate two-dimensional effec tive-medium theory. The theoretical reflectance spectra are found to be in good agreement with the experimental ones and the predicted coupled Frohlic h-plasmon modes for conducting samples were observed experimentally. The wa velength used in Raman measurements did not fulfil the requirements of effe ctive-medium theory, but the resulting spectra could be explained at least qualitatively by taking into account the diffuse scattering.