Avalanche Photodiode Edge Breakdown Suppression
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Solution Overview
Problem
Optical sensing applications, such as LiDAR systems, face challenges in achieving current gain from photodiodes without incurring unacceptable noise penalties, particularly due to edge breakdown in avalanche photodiodes, which leads to higher signal noise and reduced breakdown voltage and gain.
Innovation Solution
The design of an avalanche photodiode with an epitaxial layer and a buried layer of higher carrier concentration, along with semiconductor sublayers of opposite conductivity types, reduces edge breakdown by creating a depletion region with a higher electric field, allowing for larger reverse bias voltage and enhanced avalanche amplification while minimizing noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If reverse bias voltage is increased to achieve current gain in avalanche photodiodes, then gain is improved, but edge breakdown occurs leading to increased noise
Solution Approach 1:
The patent applies local quality by creating a guard ring structure with different doping concentration and geometry around the perimeter of the photodiode active region. This localized modification at the edges creates a different electric field distribution specifically at the vulnerable edge regions, suppressing edge breakdown while maintaining high gain in the central active region.
Solution Approach 2:
The guard ring acts as an intermediary structure between the high-field avalanche region and the substrate. It mediates the electric field distribution, preventing field concentration at the edges that would cause breakdown, while allowing the central region to maintain the high fields necessary for avalanche multiplication and current gain.
2Power
If reverse bias voltage is increased to enhance avalanche amplification, then gain is improved, but breakdown voltage is reduced
Solution Approach 1:
The guard ring structure modifies the local electric field characteristics at the periphery of the photodiode. By creating a graded doping profile and specific geometric configuration in the guard ring, the electric field is redistributed to prevent concentration at edge regions, thereby increasing the overall breakdown voltage while preserving high avalanche amplification in the active region.
Solution Approach 2:
The guard ring structure provides beforehand cushioning by preemptively managing the electric field distribution before breakdown can occur. It creates a protective buffer zone around the active region that prevents field-induced breakdown, allowing the device to operate at higher reverse bias voltages without premature failure.
3Measurement precision
If edge breakdown is suppressed to reduce noise, then signal-to-noise ratio is improved, but device complexity increases
Solution Approach 1:
Rather than redesigning the entire photodiode structure, the patent applies a localized guard ring modification at the edges. This targeted approach suppresses edge breakdown and improves signal-to-noise ratio while adding minimal structural complexity compared to a complete structural redesign.
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 configuration effectively reduces edge breakdown and noise in avalanche photodiodes, improving signal-to-noise parameters and enabling higher gain without increasing noise penalties, making them suitable for optical sensing systems like LiDAR.
Implementation Method 1
Photodetectors detect light and generate electrical signals according to the detected light
Implementation Method 2
The high electric field created with high voltage in the depletion region results in an avalanche current with gain
Data Source
AI summary
An integrated circuit includes a photodetector that has an epitaxial layer with a first conductivity type located over a substrate. A buried layer of the first conductivity type is located within the epitaxial layer and has a higher carrier concentration than the epitaxial layer. A semiconductor layer located over the buried layer has an opposite second conductivity type and includes a first sublayer over the buried semiconductor layer and a second sublayer between the first sublayer and the buried layer. The first sublayer has a larger lateral dimension than the second sublayer, and has a lower carrier concentration than the second sublayer.