Silicon Optical Modulator Dopant Profile Control
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Solution Overview
Problem
Silicon-based optical modulators face a trade-off between increasing speed and minimizing optical power loss, as reducing series resistance to achieve higher speeds often results in substantial optical absorption and loss.
Innovation Solution
Modifying the dopant profiles in the gate and body layers, particularly in intermediate regions between contact and active areas, to achieve a dopant concentration that balances low series resistance with minimal optical loss, using either uniform or graded profiles that track the inverse of optical intensity profiles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If contacts are placed close to the active region to reduce series resistance, then operating speed is improved, but optical loss increases due to high optical absorption in heavily-doped contact regions
Solution Approach 1:
The patent applies local quality by creating distinct dopant concentration zones: heavily-doped contact regions for low resistance, lightly-doped active regions for low optical absorption, and intermediate-doped transition regions that bridge these extremes. This spatial variation in dopant concentration allows each region to be optimized for its specific function, resolving the contradiction between speed and optical loss.
Solution Approach 2:
The patent introduces intermediate-doped transition regions as intermediary zones between the heavily-doped contact regions and lightly-doped active regions. These transition regions act as mediators that gradually reduce dopant concentration, providing both electrical connectivity and optical transparency, thus resolving the contradiction between low resistance and low optical loss.
2Reliability
If heavily-doped areas are placed close to optical mode in the active region, then series resistance is reduced, but optical absorption increases causing substantial power loss
Solution Approach 1:
The patent applies local quality by creating distinct dopant concentration zones: heavily-doped contact regions for low resistance, lightly-doped active regions for low optical absorption, and intermediate-doped transition regions that bridge these extremes. This spatial variation in dopant concentration allows each region to be optimized for its specific function, resolving the contradiction between speed and optical loss.
Solution Approach 2:
The patent extends the dopant profile control into the vertical dimension with graded doping profiles that transition from heavy doping at the contact interface to light doping at the optical mode region. This three-dimensional dopant distribution optimizes both electrical and optical performance by considering spatial dimensions beyond simple planar placement.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for increased operating speed of silicon-based optical modulators without significant optical power loss by optimizing dopant concentrations in intermediate regions, thereby reducing series resistance while maintaining optical signal confinement.
Implementation Method 1
Free carriers will accumulate and deplete on either side of dielectric 6 as a function of the voltages applied to SOI layer 3 (V3) and/or doped silicon layer 2 (V2). The modulation of the free carrier concentration results in changing the effective refractive index in the active region, thus introducing phase modulation of an optical signal
Implementation Method 2
The heavily-doped contact areas provide a very low resistance coupling to the contact regions
Implementation Method 3
Modifying the dopant profiles in the gate and body layers, particularly in intermediate regions between contact and active areas, to achieve a dopant concentration that balances low series resistance with minimal optical loss
Data Source
AI summary
A high speed silicon-based optical modulator with control of the dopant profiles in the body and gate regions of the device reduces the series resistance of the structure without incurring substantial optical power loss. That is, the use of increased dopant values in areas beyond the active region will allow for the series resistance to be reduced (and thus increase the modulating speed of the device) without incurring too large a penalty in signal loss. The dopant profiles within the gate and body regions are tailored to exhibit an intermediate value between the high dopant concentration in the contact areas and the low dopant concentration in the carrier integration window area.