Avalanche Photodiode Contact Layout for Lower Dark Count Rate
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Solution Overview
Problem
The increase in dark count rate (DCR) in avalanche photodiodes (APDs) due to high electric fields is a significant challenge that existing technologies have not adequately addressed.
Innovation Solution
A photoelectric conversion device is designed with a specific structure that includes a first region of a first conductivity type, a second region of a second conductivity type forming an avalanche photodiode, a separation region of the second conductivity type, a contact region of the second conductivity type, and strategically placed contact plugs. This configuration aims to minimize the impact of high electric fields on DCR.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high electric field is applied in the avalanche photodiode to enhance photoelectric conversion efficiency, then the detection sensitivity is improved, but the dark count rate increases
Solution Approach 1:
The semiconductor layer is divided into multiple functional regions: a photoelectric conversion region for detecting photons, a multiplication region for avalanche multiplication, and a separation region to isolate excess carriers. This segmentation allows the high electric field to be confined to specific regions, improving detection sensitivity while limiting dark count generation to controlled areas.
Solution Approach 2:
Different regions of the semiconductor layer are doped with different conductivity types and impurity concentrations to create locally optimized electric field distributions. The multiplication region has high impurity concentration for strong field-induced avalanche multiplication, while the separation region has low impurity concentration to reduce carrier generation and suppress dark count rate.
2Area of moving object
If the distance between contact plugs is reduced to minimize device area, then the device size is decreased, but the electric field distribution becomes non-uniform causing increased dark count rate
Solution Approach 1:
The contact plugs are positioned asymmetrically with respect to the multiplication region, with the first contact plug closer to one side and the second contact plug closer to the opposite side. This asymmetric arrangement, combined with the separation region, creates a more uniform electric field distribution across the multiplication region, reducing localized field enhancements that would increase dark count rate.
Solution Approach 2:
The separation region acts as an intermediary between the contact plugs and the multiplication region, isolating the electric field effects from the contact structures. This intermediary region prevents direct field lines from contact plugs from penetrating into the multiplication region, maintaining uniform field distribution and stable dark count rate even when contact plugs are positioned close together.
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
The proposed solution effectively suppresses the increase in dark count rate caused by high electric fields, thereby enhancing the performance and reliability of APDs in photoelectric conversion devices.
Implementation Method 1
photo charges generated by a single photon cause avalanche multiplication in the p-n junction region
Implementation Method 2
SPAD (Single Photon Avalanche Diode) in which photo charges generated by a single photon cause avalanche multiplication
Data Source
AI summary
Photoelectric conversion device incudes first region of first conductivity type arranged in semiconductor layer having first second surfaces, second region of second conductivity type arranged between the second surface and the first region and forming avalanche photodiode, separation region of the second conductivity type arranged between the first and second surfaces to surround the second region, contact region of the second conductivity type contacted to the separation region, first contact plug connected to the first region, and second contact plug connected to the contact region. The second region has shape of rectangle, and the second contact plug is arranged in diagonal direction of the rectangle. Distance between center of the first contact plug and center of the second contact plug is larger than distance between center of the second region and the center of the second contact plug.