Photodetector Substrate Depth for Faster Detection Recovery
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Solution Overview
Problem
Conventional photodetectors, such as avalanche photodiodes (APDs) and single-photon avalanche diodes (SPADs), suffer from dark current issues due to minority carriers generated in the substrate, leading to spurious signals and extended time constants in detection events, which can affect detection accuracy and increase the time required for the photodetector to return to its resting state.
Innovation Solution
Implementing techniques such as introducing surface defects, crystallographic defects, limiting substrate depth, modifying band structure, using anti-reflective layers, and band-reject optical filters to reduce minority carrier photoexcitation and mitigate dark current in photodetectors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensitive photodetectors (APD/SPAD) are used to detect light, then detection sensitivity is improved, but dark current increases causing spurious signals
Solution Approach 1:
The patent extracts and removes minority carriers (electrons and holes) that cause dark current through recombination centers introduced into the substrate. By selectively removing harmful carriers before they reach the detection region, the patent maintains high detection sensitivity while eliminating spurious signals from dark current.
Solution Approach 2:
The patent converts the harmful effect of minority carrier diffusion into a beneficial recombination process. By introducing recombination centers, the patent causes minority carriers to recombine harmlessly in the substrate rather than reaching the detection region, thus transforming the dark current problem into a solution mechanism.
2Measurement precision
If substrate depth is increased to reduce surface recombination, then detection efficiency improves, but minority carrier diffusion distance increases causing longer time constants
Solution Approach 1:
The patent applies local quality by creating specific recombination regions at controlled depths within the substrate. Rather than uniformly treating the entire substrate, the patent introduces recombination centers at specific locations where they can efficiently remove minority carriers without requiring increased substrate depth, thus maintaining both detection efficiency and short time constants.
Solution Approach 2:
The patent performs preliminary action by pre-introducing recombination centers into the substrate before minority carriers can diffuse to the detection region. This proactive approach ensures that minority carriers are removed early in their diffusion path, preventing them from reaching the detection region and causing dark current, while also reducing the overall time constant.
3Power
If light source irradiation is increased to improve signal strength, then detection signal improves, but minority carrier photoexcitation increases causing more dark current
Solution Approach 1:
The patent introduces recombination centers as intermediary elements between the light source and the detection region. These recombination centers act as mediators that capture and remove minority carriers photoexcited by the light source before they can reach the detection region. This allows the system to use higher light intensities for stronger signals while the intermediary recombination centers prevent the corresponding increase in dark current.
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
Reduces dark current, shortens the time constant of detection events, and enhances photodetector performance by minimizing spurious signals and allowing for faster return to resting state, thereby improving detection accuracy and measurement rate.
Implementation Method 1
minority carriers may be photoexcited in the substrate based on light emitted from the light source
Implementation Method 2
The surface defects allow for recombination of electrons and holes so as to mitigate dark current arising from minority carriers photoexcited in the substrate
Implementation Method 3
polishing or planarizing a backside of the substrate to prevent reflections within the substrate of the light from the light source
Implementation Method 4
introducing an anti-reflective layer to permit photons from the light source to exit the substrate
Implementation Method 5
introducing a band-reject optical filter that filters light of a wavelength corresponding to the light source
Implementation Method 6
a photodetector coupled to the substrate. The photodetector is arranged to detect light emitted from a light source that irradiates a top surface of the device
Data Source
AI summary
Example embodiments relate to controlling detection time in photodetectors. An example embodiment includes a device. The device includes a substrate. The device also includes a photodetector coupled to the substrate. The photodetector is arranged to detect light emitted from a light source that irradiates a top surface of the device. A depth of the substrate is at most 100 times a diffusion length of a minority carrier within the substrate so as to mitigate dark current arising from minority carriers photoexcited in the substrate based on the light emitted from the light source.