Pressure dependence of the optic phonon energies inAlxGa1−xAs

We have conducted an extensive Raman scattering study of the effects hydrostatic pressure has on ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As alloy phonons for 0⩽x⩽0.70. The mode-Grüneisen parameter γ is found to depend on x. The variation is monotonic in dilution and increases by 30% over the range of x studied. We find that γ for GaAs-like and AlAs-like longitudinal-optic (LO) phonons correlates with Born’s transverse dynamic effective charge on the respective alloy component. We suggest that this phenomenon is specific to alloys, and interpret it as a consequence of charge transfer on the cation sublattice. Pressure induced resonance Raman scattering is examined for x=0.40. We observe strong enhancement for both LO phonons when in resonance with the direct energy gap. © 1996 The American Physical Society.