Silicon Electro-Optic Modulator Fabricated on Silicon Substrate Utilizing the Three-Terminal Transistor Waveguide Structure

The fabrication and characterization of the three-terminal transistor-based optical waveguide modulators fabricated on silicon substrate are reported. The modulation scheme was achieved via the carrier injection, or plasma dispersion effect. The spin-on-dopant (SOD) method was conducted at 1000 °C in a mixture of nitrogen/oxygen ambient to separately pattern the heavily-doped source (n+), gate (p+), and drain (n+) regions. The corresponding p- and n-type dopant profiles were determined using the spreading resistance probe (SRP) technique, of which the highest surface concentrations of ~2.09×1020 and ~3.53×1020 cm-3 were respectively achieved. The resultant dopant concentrations and diffusion depths were found to be critically dependent on the diffusion time and temperature. The results of our experiments revealed that there are virtually little or no dependencies of the modulation depth on the gate current and modulation length. Finally, the modulators thus fabricated showed an ultra-sensitivity on the drain–source voltage (VDS), with a modulation depth close to 100% at VDS~±5 V when a 5 mA gate current was applied.