Back-Illuminated Geiger Mode Avalanche Photodiode Array
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Solution Overview
Problem
Existing avalanche photodiodes have reduced quantum efficiency and speed when detecting shorter wavelength photons due to preferential absorption in the highly doped top layer and diffusion limitations, and array implementations face area efficiency issues due to optical isolation and quenching circuitry.
Innovation Solution
The design includes a semiconductor depletion region for blue photon absorption, with charge carriers undergoing impact ionization to generate an avalanche current, and a silicon on insulator wafer-based manufacturing process forming photodiodes with electrodes on the opposite side of the buried oxide layer for improved light transmission and area utilization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If photons are absorbed in the highly doped top layer, then the device structure is simple, but quantum efficiency is reduced and speed is limited due to diffusion requirements
Solution Approach 1:
The patent inverts the conventional light absorption approach by removing the substrate and illuminating the photodiode through the buried oxide layer from the back side. This causes photons to be absorbed directly in the depletion region rather than in the highly doped top layer, eliminating the need for carrier diffusion and significantly improving quantum efficiency and response speed for blue photons
2Ease of manufacture
If carriers are generated in the highly doped region, then the device structure is simple, but speed is limited due to diffusion time requirements
Solution Approach 1:
By inverting the illumination direction and removing the substrate, the patent enables direct photon absorption in the depletion region. This eliminates the carrier diffusion step that limits speed in conventional structures, achieving sub-nanosecond response times while maintaining device simplicity
Solution Approach 2:
The patent extracts the substrate from the conventional photodiode structure, allowing illumination through the buried oxide layer. This removal enables direct absorption in the depletion region and eliminates the path that would require carriers to diffuse through the highly doped top layer, thereby improving speed
3Reliability
If optical isolation and quenching circuitry are included in arrays, then device functionality is complete, but area efficiency is reduced
Solution Approach 1:
The patent moves the electrodes to the back side of the photodiode structure, on the opposite side of the buried oxide layer from the light-receiving surface. This three-dimensional rearrangement allows optical isolation structures to be positioned between the electrodes rather than around the periphery, significantly increasing the light-sensitive area of each photodiode element in the array
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 enhances quantum efficiency and speed by absorbing blue photons directly in the depletion region, reducing diffusion times and increasing area efficiency, allowing for high-speed and efficient photodetection in photodiode arrays.
Implementation Method 1
Incident photons having a wavelength in the blue end of the visible spectrum are absorbed in the depletion region so as to generate charge carriers
Implementation Method 2
The charge carriers undergo impact ionization in the depletion region so as to generate an avalanche current in the photodiode
Data Source
AI summary
A avalanche mode photodiode array (102) is fabricated using a silicon on insulator wafer and substrate transfer process. The array includes a plurality of photodiodes (100). The photodiodes (100) include an electrically insulative layer (206), a depletion region (204), and first (208) and second (210) doped regions. An interconnection layer (212) includes electrodes (214, 216) which provides electrical connections to the photodiodes. The photodiode array (102) is carried by a handle wafer (217).