SPAD Pixel Structure With Potential Barrier for After-Pulse Suppression
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Solution Overview
Problem
Single photon avalanche diodes (SPADs) generate after-pulses, which are difficult to distinguish from light pulses and cause malfunction in light detection, leading to reduced detection efficiency due to their temporal correlation with photon detection.
Innovation Solution
A pixel structure for SPADs is designed with a third semiconductor layer of higher impurity concentration ahead of the junction, guiding electrons or holes generated through a potential barrier to a discharge path, reducing after-pulse influence by directing them away from the avalanche amplification region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a SPAD is used for light detection, then high sensitivity and single-photon detection capability are achieved, but after-pulses are generated causing detection malfunction
Solution Approach 1:
The semiconductor structure is divided into multiple functional layers: a light absorption layer for photon detection, an avalanche amplification layer for signal multiplication, and a field effect layer for electron control. This segmentation allows each layer to perform its specific function while isolating the after-pulse generation to a controlled region, preventing false detections in the light absorption layer.
Solution Approach 2:
A third semiconductor layer with higher impurity concentration is introduced as an intermediary between the avalanche amplification region and the light absorption layer. This intermediate layer creates a potential barrier that selectively blocks electrons generated by after-pulses while allowing photons to pass through to the absorption layer, thus mediating between the amplification function and detection accuracy.
2Measurement precision
If the avalanche amplification region is made larger to improve signal amplification, then detection sensitivity increases, but after-pulse generation probability increases
Solution Approach 1:
The third semiconductor layer with higher impurity concentration is localized specifically at the interface between the avalanche amplification layer and the light absorption layer. This local modification creates a potential barrier precisely where needed to block after-pulse electrons, while the rest of the avalanche amplification region maintains its larger size for sufficient signal amplification.
3Reliability
If a third semiconductor layer with higher impurity concentration is added to reduce after-pulses, then detection reliability improves, but device complexity increases
Solution Approach 1:
The third semiconductor layer is created by modifying the impurity concentration parameter of the existing semiconductor structure. Rather than adding a completely new material layer, the invention changes the electrical parameter (impurity concentration) of an existing layer to create the desired potential barrier, simplifying the manufacturing process while achieving after-pulse suppression.
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 pixel structure effectively reduces the occurrence of after-pulses, allowing for high-speed and repetitive light detection by preventing unnecessary electrons from entering the avalanche amplification region, thereby enhancing detection efficiency.
Implementation Method 1
a light absorption layer that absorbs light and generates electrons through photoelectric conversion
Implementation Method 2
The SPAD is a photodiode configured to perform avalanche amplification of electrons generated upon incidence of incident light
Data Source
AI summary
To reduce the influence of generation of after-pulses when a pixel including a SPAD is used. In a SPAD pixel, a PN junction part of a P+ type semiconductor layer and an N+ type semiconductor layer is formed, a P type semiconductor layer having a concentration higher than the concentration of a silicon substrate is formed in a region deeper than the PN junction part and close to a light absorption layer. With no quenching operation generating no after-pulse, electrons generated in the light absorption layer are guided to the PN junction part and subjected to avalanche amplification. When the quenching operation is performed after avalanche amplification, the electrons are guided to the N+ type semiconductor layer by a potential barrier to prevent avalanche amplification. The present disclosure is applicable to an image sensor including a SPAD.