Photodetector Detection-Time Control via Substrate Depth Limitation
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Solution Overview
Problem
Sensitive photodetectors in LIDAR systems, such as APDs and SPADs, face accuracy issues due to dark current caused by minority carriers generated in the substrate, which persist even after the light source is turned off, leading to spurious signals and increased time constants in detection events.
Innovation Solution
The introduction of surface defects, crystallographic defects, limited substrate depth, specific band structures, anti-reflective layers, polishing, and band-reject optical filters to mitigate dark current by reducing minority carrier diffusion and photoexcitation within the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sensitive photodetectors (APDs, SPADs) are used to detect light, then detection sensitivity is improved, but dark current increases due to minority carriers generated in the substrate
Solution Approach 1:
The patent extracts and removes the substrate from the photodetector structure, transitioning from bulk photodetectors to thin-film or substrate-free designs. This eliminates the source of minority carrier generation while preserving the active detection region, thereby reducing dark current without compromising detection sensitivity.
Solution Approach 2:
The patent applies different material compositions and doping concentrations specifically in the detection region rather than uniformly throughout the substrate. This localized optimization enhances detection sensitivity in the active area while minimizing minority carrier generation in regions that would otherwise contribute to dark current.
2Object-generated harmful factors
If surface defects are introduced to reduce dark current, then dark current reduction is improved, but detection accuracy may be affected
Solution Approach 1:
The patent removes the substrate that would require defect engineering, eliminating the trade-off between dark current reduction and detection accuracy. By using thin-film or substrate-free structures, the system achieves dark current reduction through geometric elimination rather than defect introduction, preserving detection accuracy.
Solution Approach 2:
The patent employs composite material structures with carefully engineered interfaces and doping profiles that provide both dark current suppression and maintained detection accuracy without relying on surface defects. The composite structure allows optimization of each layer's properties to simultaneously achieve both goals.
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
These techniques effectively reduce dark current, improving detection accuracy and reducing the time constant associated with illumination events, allowing for faster and more reliable photodetector performance in LIDAR systems.
Implementation Method 1
minority carriers photoexcited in the substrate based on the 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
Implementation Method 3
The photodetector is arranged to detect light emitted from a light source that irradiates a top surface of the device
Data Source
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Figure 2A
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.