Disorder-activated first-order Raman scattering by acoustic phonons in electron-irradiated GaP crystals

Laser Raman spectroscopic studies of electron beam irradiated gallium phosphide monocrystals have been performed. The samples were exposed to a beam of 7.3 MeV electrons at 77 K, the fluence of electrons was varied from 3 x 1015 to 3 x 1018 cm-2. The first-order Raman spectra of GaP single crystals recorded at 80 K under 488.0 nm laser light excitation are shown. The frequencies of the fundamental LO and TO modes are seen not to be affected by irradiation and to be independent of the fluence of electrons. The additional bands at 100 and 220 cm-1 correspond to scattering by disorder-activated transverse- and -longitudinal acoustic phonons