Picosecond Raman scattering from photoexcited plasmas in GaAs and InP: The important role of interfacial recombination

Picosecond Raman scattering is used to compare the properties of coupled nonequilibrium plasmon–LO-phonon modes in photoexcited GaAs and InP. The dependence of the coupled-mode line shape on carrier density is qualitatively the same for uncoated InP and for GaAs when it is overcoated with a thin layer of ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As. Radically different results obtained from bare GaAs are explicitly attributed to the highly inhomogeneous nature of the optically excited plasma at air-GaAs interfaces.