Photo Sensor Buffer Structure for Low-Dark-Current Pixel Scaling
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Solution Overview
Problem
The challenge in photo sensing devices is the increased dark current due to lattice mismatch between semiconductor materials, leading to dislocation defects and degraded performance, especially as pixel sizes decrease, affecting signal-to-noise ratio and device reliability.
Innovation Solution
A photo sensing device design that includes a semiconductor stack with alternating layers of silicon and germanium, forming a buffer between the photosensitive germanium layer and the silicon substrate, which alleviates lattice mismatch and reduces dislocation defects by having a lattice constant closer to the photosensitive material, and surface smoothing techniques to improve epitaxial growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pixel size is reduced to increase device integration, then device complexity is reduced and productivity is improved, but dark current increases and signal-to-noise ratio deteriorates
Solution Approach 1:
A semiconductor stack comprising alternating layers of first semiconductor material and second semiconductor material is introduced as an intermediary structure between the photosensitive member and the substrate. This stack acts as a mediator that gradually transitions the lattice constant, reducing the abrupt mismatch at the interface and minimizing dislocation defects that would otherwise increase dark current and degrade signal-to-noise ratio in scaled-down pixel devices
2Device complexity
If photosensitive member is directly formed on substrate, then device complexity is minimized, but lattice mismatch causes dislocation defects and increased dark current
Solution Approach 1:
The interface between the photosensitive member and substrate is segmented into multiple thin layers of alternating semiconductor materials with different lattice constants. This segmentation creates a gradual lattice constant transition rather than a single abrupt interface, reducing dislocation defects and dark current while maintaining reasonable device complexity through the use of thin-film deposition techniques
3Reliability
If alternating semiconductor layers are introduced to reduce lattice mismatch, then dislocation defects are reduced and dark current decreases, but device complexity increases
Solution Approach 1:
The lattice constant parameter is gradually changed through the alternating semiconductor layers, creating a transition zone that reduces dislocation defects. By controlling the thickness and composition of each layer, the patent achieves effective lattice mismatch reduction while keeping the overall structure manageable through precise parameter control rather than complex multi-component designs
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 effectively reduces dark current, enhances device performance, and improves signal collection by minimizing lattice mismatch and surface roughness, leading to better signal-to-noise ratio and increased reliability.
Implementation Method 1
lattice mismatch between semiconductor materials, leading to dislocation defects
Implementation Method 2
absorb radiation projected thereto and convert the sensed radiation into electrical signals
Data Source
AI summary
The present disclosure provides a photo sensing device including a substrate, including a silicon layer at a front surface, a photosensitive member extending into and at least partially surrounded by the silicon layer, wherein the silicon layer includes a first doped region adjacent to a first side of the photosensitive member, wherein the first doped region has a first conductivity type, and a second doped region adjacent to a second side of the photosensitive member opposite to the first side, wherein the second doped region has a second conductivity type different from the first conductivity type, and a composite layer disposed between the photosensitive member and the silicon layer and surrounding the photosensitive member, and a portion of the composite layer proximal to the first doped region is doped with a dopant having the first conductivity type.