Optical modulator using monocrystalline and polycrystalline silicon

A method, comprising:

• forming a lower waveguide from monocrystalline silicon doped to exhibit a first conductivity type, wherein the lower waveguide includes:
• a lower hub;
• a first lower wing that extends in a first direction from the lower hub;
• a second lower wing that extends in a second direction from the lower hub;
• and
• a lower ridge that extends upward from the lower hub, wherein the lower ridge is doped less than the first lower wing and the second lower wing;
• depositing a gate oxide layer on an upper surface of the lower waveguide;
• forming an upper waveguide, doped to exhibit a second conductivity type that is different from the first conductivity type, wherein the upper waveguide includes:
• an upper ridge, made of monocrystalline silicon, that is aligned with the lower ridge on a first axis and extends upward from the gate oxide layer to form a waveguide region with the lower ridge and the gate oxide layer;
• a first upper wing, made of polycrystalline silicon that is doped greater than the upper ridge, that extends in the first direction perpendicularly from the upper ridge;
• a second upper wing, made of polycrystalline silicon that is doped greater than the upper ridge, that extends in the second direction perpendicularly from the upper ridge;
• and
• an upper hub, made of polycrystalline silicon, that extends upward from the upper ridge, is aligned with the upper ridge on the first axis, and is aligned with the first upper wing and the second upper wing on a second axis perpendicular to the first axis.