Raman scattering lineshapes in GaAs and InP

We report Raman spectra of InP and GaAs in the vicinity of 1LO phonon energy, with a spectral resolution of 0.2 cm(-1) which is sufficient to see broadening associated with the anharmonic decay lifetime of the LO mode. New phenomena become apparent when resonant excitation is used. Near to the 1LO phonon energy, the scattering from InP occurs at different values of Stokes' shift when measured in parallel and perpendicular linear polarisations, with the larger shift in the perpendicular case. The deconvolved full width at half maximum (FWHM) for the phonon at 4 K is 0.2(2) cm(-1), corresponding to 48 ps phonon dephasing time. The splitting between the two lines depends on injection power and is of the order of 0.3-0.6 cm(-1), and so has been unresolved in all previous studies. When surface recombination is suppressed GaAs shows the same two-mode structure as InP, thus confirming the assignment of the higher-energy mode to excitations of the photoinjected plasma. Copyright (C) 1996 Elsevier Science Ltd