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

Photocarrier diffusion in Si at ambient temperature in the carrier density range of 4×10¹⁷ to 4×10¹⁹cm^-3 has been characterized by the transient grating technique. Measurements show a strong density dependence in ambipolar diffusivity with a minimum of 4.7cm²s^-1, a factor of 4 lower than the intrinsic value, at 10¹⁹cm^-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.