Geiger-Mode Avalanche Photodiode Gettering for Low Crosstalk Noise
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Solution Overview
Problem
Geiger-mode avalanche photodiodes (GMAPs) suffer from optical crosstalk and increased dark-noise rates due to secondary photons emitted during avalanche multiplication, which reduces their detection efficiency and makes it difficult to quench avalanche currents in a timely manner, especially in large arrays operating at high biasing voltages.
Innovation Solution
The design includes a semiconductor body with a specific epitaxial layer structure and gettering regions to reduce the lifetime of minority carriers, preventing secondary photons from interfering with adjacent photodiodes, thereby reducing afterpulsing and delayed crosstalk. This is achieved by creating a semiconductor structure with epitaxial layers of varying doping levels and gettering regions with high lattice defectiveness to quickly recombine minority carriers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If Geiger-mode avalanche photodiodes operate at high reverse-biasing voltages above breakdown voltage, then avalanche carrier multiplication gain is achieved, but optical crosstalk and afterpulsing increase due to secondary photons and minority carriers
Solution Approach 1:
The patent extracts and removes harmful minority carriers from the system by introducing gettering regions that act as traps, separating the harmful carriers from the useful detection function. This allows the photodiode to maintain high gain operation while removing the source of optical crosstalk and afterpulsing.
Solution Approach 2:
The gettering regions serve as intermediary elements between the depleted region and the substrate, capturing minority carriers before they can cause harmful effects. These intermediary trap regions mediate the interaction between high voltage operation and noise reduction.
2Measurement precision
If the depleted region volume is increased to improve photon detection efficiency, then more secondary photons are generated through electroluminescence, but optical crosstalk to adjacent photodiodes increases
Solution Approach 1:
The patent converts the harmful secondary photons into a beneficial effect by having them absorbed by the substrate and generating minority carriers that are then captured by gettering regions. The harmful electroluminescence photons are transformed into trapped carriers that cannot cause crosstalk.
Solution Approach 2:
The substrate acts as an intermediary layer that absorbs secondary photons and converts them to minority carriers, which are then captured by gettering regions. This intermediary conversion process prevents direct optical crosstalk while maintaining detection efficiency.
3Productivity
If minority carrier lifetime is extended to improve carrier collection efficiency, then carriers can diffuse to adjacent photodiodes, but afterpulsing and delayed crosstalk increase
Solution Approach 1:
The patent extracts minority carriers from the diffusion path by introducing gettering regions that trap them before they can diffuse to adjacent photodiodes. This removal of carriers eliminates the mechanism for afterpulsing and delayed crosstalk while maintaining collection efficiency through the primary detection mechanism.
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
This approach results in a low-noise Geiger-mode avalanche photodiode with reduced crosstalk and dark-noise rates, allowing for high-sensitivity detection without the need to decrease the biasing voltage or photodiode size, thus maintaining a high fill factor and signal-to-noise ratio in large arrays.
Implementation Method 1
generation of a single electron-hole pair, caused by absorption in the depleted region of a photon impinging upon the SPAD
Implementation Method 2
This ionization process in turn causes an avalanche carrier multiplication, with gains of around 10^6
Implementation Method 3
the SPADs operating above the breakdown voltage, and in particular the corresponding depleted regions, emit in an isotropic way secondary photons, on account of different mechanisms such as (direct and indirect) interband recombinations
Implementation Method 4
this minority carrier (for example, a hole, in the case of a substrate of an N type) can diffuse until the depleted region of i) the original SPAD or else ii) another SPAD of the array is reached
Data Source
AI summary
In at least one embodiment, a Geiger-mode avalanche photodiode, including a semiconductor body, is provided. The semiconductor body includes a semiconductive structure and a front epitaxial layer on the semiconductive structure. The front epitaxial layer has a first conductivity type. An anode region having a second conductivity type that is different from the first conductivity type extends into the front epitaxial layer. The photodiode further includes a plurality of gettering regions in the semiconductive structure.