Photoexcited carrier diffusion near a Si(111) surface: Non-negligible consequence of carrier-carrier scattering

Abstract

Photocarrier diffusion in Si at ambient temperature in the carrier density range of $4\ifmmode\times\else\texttimes\fi{}{10}^{17}$ to $4\ifmmode\times\else\texttimes\fi{}{10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}$ has been characterized by the transient grating technique. Measurements show a strong density dependence in ambipolar diffusivity with a minimum of $4.7{\mathrm{cm}}^{2}{\mathrm{}\mathrm{s}}^{\mathrm{\ensuremath{-}}1},$ a factor of 4 lower than the intrinsic value, at ${10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}.$ The decrease is a result of carrier-carrier scattering at high densities. Measurements on both a Si(111) surface (reflection geometry) and a Si film (transmission geometry) indicate that there is no significant surface effect in diffusivity for carriers generated near the surface.