Optical phonons of circular wires in porous GaP

The reflection spectra of porous gallium phosphide samples are investigated in the far infrared region of wave numbers (10-700 cm(-1)). In addition of the longitudinal and transverse optical phonon modes corresponding to the bulk material, additional vibrational modes are detected. Their number and spectral position are correctly described by a model of a dispersive dielec tric medium under the assumption that porous gallium phosphide is formed by crystallites whose shape is close to cylindrical. It is concluded that suc h vibrational modes are optical phonons confined by the volume of the quant um wire. The experimental optical reflection spectra are used to obtain est imates of the average diameter of nanocrystallites forming the porous GaP l ayer. (C) 2001 MAIK "Nauka/Interperiodica".