Silicon electro-optical modulator
Disclosed are designs and methods of fabrication of silicon carrier-depletion based electro-optical modulators having doping configurations that produce modulators exhibiting desirable modulation efficiency, optical absorption loss and bandwidth characteristics. The disclosed method of fabrication of a modulator having such doping configurations utilizes counter doping to create narrow regions of relatively high doping levels near a waveguide center.
1. An electro-optical modulator, comprising:
a semiconductor material waveguide having four doped regions of a same dopant type but different doping concentrations, wherein
the four doped regions include first, second, third, and fourth doped regions, wherein the first doped region is closest to a center of the semiconductor material waveguide compared to the second and third doped regions, the second doped region is laterally between the first and third doped regions, and the fourth doped region is laterally adjacent to the third doped region such that the third doped region is between the second and fourth doped regions, wherein the third doped region has a greater doping concentration than the first doped region and the first doped region has a greater doping concentration than the second doped region, and wherein the fourth doped region has a greater doping concentration than the third doped region.
2. The electro-optical modulator of claim 1 , wherein the third doped region is outside an optical mode field in the semiconductor material waveguide.
3. The electro-optical modulator of claim 1 , wherein one of the four doped regions extends from a core of the semiconductor material waveguide to a slab of the semiconductor material waveguide.
4. The electro-optical modulator of claim 1 , wherein the first and second doped regions are at least partially within a ridge of the semiconductor material waveguide.
5. The electro-optical modulator of claim 1 , wherein the second doped region extends from a core of the semiconductor material waveguide to a slab of the semiconductor material waveguide.
6. The electro-optical modulator of claim 1 , wherein the first doped region has a width of 150 nm or less.
7. The electro-optical modulator of claim 1 , wherein a doping concentration of the second doped region is a concentration of net activated dopants.
8. The electro-optical modulator of claim 1 , wherein the same dopant type is n-type.
9. The electro-optical modulator of claim 1 , wherein the same dopant type is p-type.
10. The electro-optical modulator of claim 1 , wherein the four doped regions are laterally arranged with respect to each other along a direction perpendicular to a direction of travel of light in the semiconductor material waveguide.