Backside Photodetector Texture Layout for Long-Wavelength Sensitivity
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Solution Overview
Problem
Back-illuminated semiconductor photodetectors face challenges in enhancing spectral sensitivity characteristics, particularly in the long wavelength range, due to carrier recombination and stress-induced dark currents, which affect detection sensitivity and leakage currents.
Innovation Solution
The photodetector design includes a semiconductor substrate with a textured surface on one region and a non-textured surface on another, where the textured surface is positioned closer to the light incident surface, reducing carrier recombination and stress, and the thickness of the textured region is optimized to minimize dark currents and leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the thickness of the second semiconductor region is increased to reduce stress and dark currents, then reliability improves, but carrier recombination increases and spectral sensitivity deteriorates
Solution Approach 1:
The second semiconductor region is segmented into two distinct regions: a first region with a textured surface and a second region without a textured surface. This segmentation allows each region to have optimized thickness for its specific function - the first region for light absorption and the second region for stress reduction and dark current suppression.
Solution Approach 2:
Different regions of the second semiconductor region are given different local properties: the first region has a textured surface and specific thickness for maximizing light absorption, while the second region has a smooth surface and different thickness for minimizing carrier recombination and stress-induced dark currents. This local differentiation resolves the contradiction between absorption efficiency and carrier loss.
2Measurement precision
If the distance between the textured surface and pn junction is reduced to improve spectral sensitivity, then carrier recombination decreases, but stress concentration increases and dark currents worsen
Solution Approach 1:
The second semiconductor region is divided into two regions with different thicknesses. The first region (with textured surface) has smaller thickness to reduce carrier recombination distance, while the second region (without textured surface) has larger thickness to reduce stress concentration and dark currents.
Solution Approach 2:
The first region is designed with specific local properties (textured surface, smaller thickness) for maximizing light absorption and minimizing carrier recombination, while the second region has different local properties (smooth surface, larger thickness) for stress distribution and dark current suppression. This local quality differentiation allows simultaneous optimization of sensitivity and dark current characteristics.
3Measurement precision
If light absorption path is extended to improve long wavelength sensitivity, then spectral response improves, but carrier recombination in the second semiconductor region increases
Solution Approach 1:
The second semiconductor region is segmented into a first region for light absorption (with textured surface and smaller thickness) and a second region for carrier collection (without textured surface and larger thickness). This segmentation ensures that light absorption occurs in the first region where carriers are generated close to the pn junction, minimizing recombination loss, while the second region provides a buffer zone for stress management.
Solution Approach 2:
The patent converts the potential harm of extended light absorption paths (which would increase carrier recombination) into a benefit by using the textured surface in the first region to enhance light absorption efficiency through light scattering and multiple reflections, allowing shorter effective absorption paths while maintaining high spectral sensitivity.
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 configuration improves spectral sensitivity in the long wavelength range by reducing carrier recombination and dark currents, while preventing alloy spikes from reaching the pn junction, thus enhancing detection sensitivity and reducing leakage currents.
Implementation Method 1
The light having reached the textured surface is reflected or diffused at the textured surface, and further travels in the semiconductor substrate
Implementation Method 2
The light in the long wavelength range travels a long distance within the semiconductor substrate, and thus is absorbed by the semiconductor substrate
Implementation Method 3
Each of the plurality of second semiconductor regions constitutes a pn junction with the first semiconductor region
Implementation Method 4
Back-illuminated semiconductor photodetector
Data Source
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AI summary
A semiconductor substrate includes a first main surface and a second main surface opposing each other. The semiconductor substrate includes a first semiconductor region of a first conductivity type, and a plurality of second semiconductor regions constituting pn junctions with the first semiconductor region. The semiconductor substrate includes the plurality of second semiconductor in a side of the second main surface. Each of the plurality of second semiconductor regions includes a first region including a textured surface, and a second region where a bump electrode is disposed. A thickness of the first region at a deepest position of recesses of the textured surface is smaller than a distance between a surface of the second region and the deepest position in a thickness direction of the semiconductor substrate. The first main surface is a light incident surface of the semiconductor substrate.