Avalanche Photodiode Layout for Uniform Breakdown Voltage
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Solution Overview
Problem
Avalanche photodiode sensors exhibit significant variation in characteristics due to high impurity concentration in the n-type semiconductor region, leading to variations in breakdown voltage and photon detection efficiency.
Innovation Solution
The design includes a first semiconductor region with a different impurity concentration forming the pn junction, a low-impurity-concentration region, and strategically positioned contact regions to reduce impurity concentration variation and improve photon detection efficiency, while incorporating a charge accumulation layer and on-chip lens for enhanced performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the n-type semiconductor region is configured to have a high impurity concentration to enable contact formation, then the contacts can be disposed, but the variation in impurity concentration becomes large leading to variation in sensor characteristics
Solution Approach 1:
The patent divides the n-type semiconductor region into two distinct zones: a first n-type semiconductor region with high impurity concentration for contact formation, and a second n-type semiconductor region with low impurity concentration for avalanche multiplication. This local differentiation allows each region to optimize its function independently, resolving the contradiction between ease of manufacture (contact formation in high impurity region) and manufacturing precision (low variation in the low impurity region that forms the sensor characteristics).
2Ease of manufacture
If the impurity concentration in the n-type semiconductor region is high, then contacts can be formed, but the variation in characteristics such as breakdown voltage becomes large
Solution Approach 1:
The patent implements local quality by creating spatially differentiated impurity concentrations within the n-type semiconductor region. The first region (high impurity) supports contact formation while the second region (low impurity, specifically 1×10^16 to 1×10^18 atoms/cm³) ensures consistent breakdown voltage and photon detection efficiency. This resolves the contradiction by confining the manufacturing-friendly high impurity zone to areas where it doesn't affect sensor characteristics.
Solution Approach 2:
The n-type semiconductor region is segmented into functionally distinct sub-regions: a contact region with high impurity concentration and an avalanche region with low impurity concentration. This segmentation allows independent optimization of each function - contacts can be formed in the high impurity region without compromising the uniformity and reliability of the low impurity avalanche region where sensor characteristics are determined.
3Ease of manufacture
If a separation region is used to separate avalanche photodiodes, then the photodiodes can be separated, but dark current is generated due to interface levels
Solution Approach 1:
The patent introduces a p-type semiconductor region as an intermediary between adjacent n-type semiconductor regions. This p-type region acts as a mediator that prevents electron diffusion from one n-type region to another across the separation region, thereby blocking the generation of dark current through interface levels while still allowing physical separation of the photodiodes for manufacturing purposes.
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 reduces the variation in avalanche photodiode sensor characteristics, enhances photon detection efficiency, and prevents dark current issues, leading to improved reliability and sensitivity.
Implementation Method 1
A strong electric field is formed at the pn junction when a reverse voltage is applied to the anode and cathode, and the avalanche multiplication of the carriers generated in the well layer can be performed.
Implementation Method 2
Avalanche breakdown due to a high electric field can be used to multiply the carriers generated by a photoelectric effect and improve sensitivity.
Implementation Method 3
The hole accumulation layer is located below the anode at a position adjacent to the separation region. That is, the hole accumulation layer is disposed between the separation region and the well layer. Holes are accumulated in this hole accumulation layer. The accumulated holes can trap the electrons generated at the interface, and the dark current can be reduced.
Data Source
AI summary
To reduce a variation in the characteristics of avalanche photodiode sensors. An avalanche photodiode sensor includes a first semiconductor region, a second semiconductor region, a low-impurity-concentration region, a first contact region, and a second contact region. The first semiconductor region is disposed on a surface of a semiconductor substrate. The second semiconductor region is disposed below the first semiconductor region and has a different conductivity type from the first semiconductor region. The low-impurity-concentration region is disposed adjacent to the second semiconductor region. The first contact region is disposed on the surface of the semiconductor substrate to be adjacent to the first semiconductor region and has electrodes connected thereto. The second contact region is disposed adjacent to the low-impurity-concentration region and has electrodes connected thereto.