Photodiode Absorption Geometry for Space Charge Reduction
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Solution Overview
Problem
Existing photodiodes experience gain saturation when handling high-speed, strong optical signals, leading to degradation in bandwidth and gain due to spatial charge distribution in the depletion region.
Innovation Solution
The use of a photodiode with a non-rectangular absorption region geometry and an optical splitter to split the optical signal, reducing the incident power on each portion of the absorption region and minimizing space charge effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the average transmitted optical power is increased to improve data transmission capability, then the optical signal strength is improved, but the photodiode's bandwidth and gain begin to degrade due to gain saturation
Solution Approach 1:
The absorption region is divided into multiple portions (first portion, second portion, etc.) with different geometries. Each portion receives a fraction of the incident optical power, preventing any single region from experiencing excessive space charge accumulation that would cause gain saturation. This segmentation allows the photodiode to handle higher total optical power while maintaining bandwidth and gain performance.
Solution Approach 2:
Different portions of the absorption region are designed with different geometries (e.g., rectangular, triangular, trapezoidal) to create local variations in how optical power is absorbed. This ensures that high optical power is distributed non-uniformly across the absorption region, with certain areas absorbing more power and others absorbing less, thereby preventing uniform space charge buildup that leads to gain saturation.
2Power
If high optical power is transmitted to improve signal strength, then the data transmission capability is improved, but large space charge distribution is induced in the depletion region which masks the depletion field
Solution Approach 1:
The absorption region is segmented into multiple portions that collectively absorb the incident optical power. By distributing the absorption across multiple regions rather than concentrating it in a single rectangular region, the space charge generation is spread out, preventing the formation of large localized space charge distributions that would mask the depletion field and reduce carrier collection efficiency.
Solution Approach 2:
The geometry parameters of the absorption region portions are specifically designed (different shapes, sizes, and configurations) to control the spatial distribution of optical power absorption. This geometric parameter optimization ensures that the space charge distribution remains manageable even at high optical power levels, maintaining effective depletion field operation.
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 higher incident optical power while maintaining or improving the conversion to electrical signals, thereby enhancing gain bandwidth and reducing noise and space charge effects.
Implementation Method 1
an absorption region, configured to receive the optical signal from the optical coupler and convert the optical signal to an electrical signal
Data Source
AI summary
To improve an optical signal to electrical signal of a photodiode (PD) which is part of an integrated circuit, the PD can be modified to reduce noise and improve the gain bandwidth. In some aspects, the absorption region of the PD can utilize a non-rectangular geometry, for example, a clipped tapered geometry which can absorb the optical signal in more linearly than a rectangular geometry. In some aspects, the input optical signal can be split into two or more split optical signals, where each split optical signal is directed toward a different portion of the absorption region. The incident power of the optical signal transmitted to each respective portion of the absorption region can be reduced by dividing the incident power by the number of split optical signals thereby improving the gain and bandwidth saturation of each portion of the absorption region.