HOLE-PLASMON DAMPING ON HEAVILY DOPED P-TYPE GAAS(110)

The free-carrier-induced plasma excitation in heavily doped p-type GaAs(110) is studied by means of high-resolution electron-energy-loss spectroscopy. This surface hole-plasmon feature is very broad and approximately centered at 60 meV. The large broadening is due to the low hole mobility and its value depends on the energy of the incident-electron beam. Two causes can concur to determine this behavior: the momentum dependence of the Landau damping of the plasmon (due to the nonlocal nature of the free-carrier response) and the dependence of the hole mobility on the distance from the surface in the crystal. Measurements performed after increasing hydrogen exposures, which modify the subsurface charge region, allowed us to conclude that the momentum dependence of the Landau damping is the cause of the observed variation of the plasmon damping with the primary beam energy.