Figure 4. Light-induced surface carrier density in Si waveguides.

Density of free carriers ΔN_s located on the surface of the 1-μm wide waveguide at the core/cladding interface (indicated with dark grey in the inset). The carrier density obtained from the optical loss measurement of Figs 2 and 3 (blue circles) is in good agreement with that provided in the electrical domain by a surface-state photodetector (red triangles).