PRESSURE-DEPENDENCE OF THE OPTIC PHONON ENERGIES IN ALXGA1-XAS

We have conducted an extensive Raman scattering study of the effects h ydrostatic pressure has on AlxGa1-xAs alloy phonons for 0 less than or equal to x less than or equal to 0.70. The mode-Gruneisen parameter g amma is found to depend on x. The variation is monotonic in dilution a nd increases by 30% over the range of x studied. We find that gamma fo r GaAs-like and AlAs-like longitudinal-optic (LO) phonons correlates w ith 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 sublat tice. Pressure induced resonance Raman scattering is examined for x = 0.40. We observe strong enhancement for both LO phonons when in resona nce with the direct energy gap.