Semiconductor Photodetector Noise Reduction via Linear Mode APD
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Solution Overview
Problem
Conventional photon-counting type photodetectors using Geiger mode avalanche photo diodes (APDs) suffer from high dark noise and multiplication noise, making it difficult to distinguish signal from noise and limiting their ability to detect very weak light, especially random light sources like radiation.
Innovation Solution
A semiconductor photodetector design incorporating a unit pixel with a photoelectric conversion part, charge storage part, and detection circuit, where the charge multiplication region is selectively formed to minimize dark noise and multiplication noise by operating in the linear mode, allowing for the detection of very weak light containing random light.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Geiger mode APD is used to detect very weak light, then the detection capability for single photons is improved, but the dark noise and multiplication noise increase significantly
Solution Approach 1:
The photodetector is divided into multiple pixels (e.g., 3x3 matrix), with each pixel containing an APD and associated readout circuitry. This segmentation allows parallel detection across multiple elements while maintaining low noise performance in each individual pixel, thereby improving overall detection capability without proportionally increasing noise.
Solution Approach 2:
The patent optimizes the APD operation voltage to be slightly below the breakdown voltage, creating a localized optimal operating condition that balances multiplication gain with noise suppression. This local quality adjustment ensures each pixel operates at the最佳 point between sensitivity and noise, rather than using uniform high-gain Geiger mode across all pixels.
2Measurement precision
If a Geiger mode APD is used to detect very weak light, then the detection capability for single photons is improved, but the multiplication noise increases making signal distinction difficult
Solution Approach 1:
The patent implements dynamic control of the APD operation voltage, adjusting it to optimal levels below breakdown voltage based on detection requirements. This dynamic adjustment allows the system to maintain sufficient multiplication gain for single-photon detection while suppressing excessive multiplication noise that would degrade signal distinction capability.
Solution Approach 2:
The patent incorporates readout circuits that provide feedback on the detected signal levels, enabling the system to adjust operation parameters to maintain optimal signal-to-noise ratio. This feedback mechanism helps distinguish true photon signals from multiplication noise by continuously monitoring and adjusting the detection parameters.
3Measurement precision
If a PMT is used for detecting weak light, then the detection capability is improved, but the device size increases making pixel multiplication difficult
Solution Approach 1:
The patent replaces the vacuum tube-based PMT mechanical system with a solid-state APD-based photodetector array. This substitution dramatically reduces the device size from centimeter-scale PMTs to millimeter-scale integrated semiconductor pixels, enabling high-density pixel arrays while maintaining weak light detection capability through avalanche multiplication in the APDs.
Solution Approach 2:
The patent integrates multiple functional components (APD, readout circuitry, voltage biasing) into nested hierarchical structures where smaller components are integrated within larger pixel elements, which are then arranged in dense arrays. This nesting approach maximizes the number of pixels within a compact form factor, achieving high pixel density without proportionally increasing overall device size.
4Measurement precision
If a PMT is used for two-dimensional imaging, then imaging capability is achieved, but real-time capture is difficult due to scanning requirements
Solution Approach 1:
The patent divides the imaging detector into a two-dimensional array of independent pixels (e.g., 3x3 matrix), where each pixel can detect photons simultaneously. This segmentation eliminates the need for mechanical scanning required by single-element PMTs, enabling parallel detection across the entire field of view and achieving real-time imaging capability.
Solution Approach 2:
The patent transitions from one-dimensional sequential detection (scanning) to two-dimensional parallel detection by arranging pixels in a matrix configuration. This dimensional change allows simultaneous detection across multiple spatial locations, dramatically improving imaging speed and enabling real-time capture of dynamic scenes.
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 solution significantly reduces dark noise and multiplication noise, enabling the detection of very weak light with improved signal-to-noise ratio, allowing for real-time imaging and detection of random light sources without the need for synchronization with a light source.
Implementation Method 1
a charge multiplication region in which incident light is converted into a charge, and the charge is multiplied by avalanche multiplication
Implementation Method 2
a photoelectric conversion part, a charge storage part, and a detection circuit, wherein the photoelectric conversion part includes a charge multiplication region in which incident light is converted into a charge
Data Source
AI summary
A semiconductor photodetector has at least one unit pixel having a photoelectric conversion part, a charge storage part, and a detection circuit. The photoelectric conversion part includes a charge multiplication region in which incident light is converted into a charge, and the charge is multiplied by avalanche multiplication. The charge storage part is connected to the photoelectric conversion part and stores a signal charge from the photoelectric conversion part. The detection circuit is connected to the charge storage part, converts the signal charge stored in the charge storage part into a voltage, passes the voltage through an amplifier to amplify the voltage, and outputs the amplified voltage.