A semiconductor structure includes a photonic modulator and a field effect transistor on a same substrate. The photonic modulator includes a modulator semiconductor structure and a semiconductor contact structure employing a same semiconductor material as a gate electrode of a field effect transistor. The modulator semiconductor structure includes a lateral p-n junction, and the semiconductor contact structure includes another lateral p-n junction. To form this semiconductor structure, the modulator semiconductor structure in the shape of a waveguide and an active region of a field effect transistor region can be patterned in a semiconductor substrate. A gate dielectric layer is formed on the modulator semiconductor structure and the active region, and is subsequently removed from the modulator semiconductor structure. A semiconductor material layer is deposited, patterned, and doped with patterns to form a gate electrode for the field effect transistor and the semiconductor contact structure for the waveguide.