Measuring photocarrier diffusivity near a Si(111) surface by reflective two-color transient grating scattering

Photocarrier diffusion within several hundred angstroms of a Si(111) surface was studied by the transient grating technique in the reflection geometry with independently tunable pump and probe picosecond laser pulses. A monotonous decay of the diffraction signal on 10−10 s scale immediately following the carrier excitation pulse was observed and attributed to band edge carrier diffusion. The ambipolar diffusivity at photocarrier density of 2×1019 cm−3 is determined to be 4.7 cm2/s.