PHOTOEXCITATION OF COUPLED PLASMON LO PHONON MODES IN ALXGA1-XAS

We report the micro-Raman scattering by a photoexcited plasma coupled to LO phonon modes in Al(x)Ga(1-x)As at power densities as high as 1.3 x 10(6) W cm-2. There are two polar modes, so three branches of the c oupled plasmon-LO phonon dispersion are expected, but two of those are experimentally observed and only for phonon-like characteristics. Thi s means that the inhomogeneous photoexcited plasma hardly affects the line frequencies, unlike the behaviour of the homogeneous plasma produ ced by doping. Still, altering the high power photoexcitation modifies the various line intensity ratios significantly. We show that by vary ing the free carrier concentration, either by restricting the probe to high densities produced in the central part of the beam or by reducin g the free carrier concentration due to traps created by ion implantat ion, the intensities and the widths of the Raman lines could be contro lled.