Nonlocal theory of collective excitations in doped semiconducting films: The effect of depletion and accumulation layers

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Abstract
We discuss the collective electronic excitations of semiconducting films, through use of the random-phase approximation, and wave functions generated from an appropriate self-consistent potential. The calculations are carried out for n-type GaAs, with depletion or accumulation layers induced by suitable charge sheets on the film surfaces. We find and discuss the properties of surface plasmons and standing-wave bulk plasmons, and in the case of a strong accumulation layer we also find collective modes localized in the accumulation region that are only weakly Landau damped even at rather large wave vectors. We apply our calculations to the description of electron-energy-loss studies of semiconducting films.