Photocarrier diffusion in Si at ambient temperature in the carrier density range of $4\times {10}^{17}$ to $4\times {10}^{19}{\mathrm{cm}}^{\mathrm{-}3}$ has been characterized by the transient grating technique. Measurements show a strong density dependence in ambipolar diffusivity with a minimum of $4.7{\mathrm{cm}}^2{\mathrm{}\mathrm{s}}^{\mathrm{-}1},$ a factor of 4 lower than the intrinsic value, at ${10}^{19}{\mathrm{cm}}^{\mathrm{-}3}.$ 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.

• Received 29 May 1997

DOI:https://doi.org/10.1103/PhysRevB.56.15252