Semiconductor Detector Charge Trapping Barrier
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Solution Overview
Problem
Semiconductor-based detectors for electromagnetic or particle radiation face challenges in achieving high charge collection efficiency while minimizing photodiode capacitance and cross-talk between pixels, leading to reduced image sharpness and increased noise performance.
Innovation Solution
A detector structure with a third region of higher doping density than the substrate, acting as a charge-trapping barrier, is implemented to guide charge carriers towards the photodiode junction, reducing cross-talk and maintaining minimal photodiode capacitance, and a fourth region with even higher doping levels is used to control the operation of unrelated junctions independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the photodiode junction size is minimized to reduce photodiode capacitance, then noise performance is improved, but charge collection efficiency decreases due to increased cross-talk between pixels
Solution Approach 1:
A third region with higher doping density than the substrate is introduced as an intermediary charge-trapping barrier between the photodiode junction and unrelated junctions. This intermediate region captures charge carriers that would otherwise diffuse to neighboring pixels, reducing cross-talk while allowing the photodiode junction to remain small for low capacitance operation.
Solution Approach 2:
The doping density is varied locally across different regions: the substrate has a base doping density, the photodiode junction region maintains low doping for large depletion volume, while the third region has higher doping density specifically to create charge-trapping barriers. This local variation in doping quality enables simultaneous optimization of charge collection and cross-talk reduction.
2Quantity of substance
If the photodiode junction size is minimized, then photodiode capacitance is reduced, but cross-talk between neighboring pixels increases
Solution Approach 1:
The third region acts as an intermediary barrier that intercepts charge carriers before they can diffuse to neighboring pixels. By positioning this higher-doping region between the small photodiode junction and unrelated junctions, cross-talk is reduced without requiring an increase in photodiode junction size.
3Device complexity
If unrelated junctions are placed near the photodiode for compact pixel design, then device complexity is reduced, but charge collection efficiency decreases due to charge theft by unrelated junctions
Solution Approach 1:
The third region serves as a protective intermediary that prevents charge carriers from being stolen by unrelated junctions. This allows unrelated junctions to be positioned close to the photodiode for compact pixel design while the third region ensures that generated charges are funneled to the correct photodiode junction.
Solution Approach 2:
The doping density is locally increased in the third region surrounding the photodiode junction, creating localized charge-trapping barriers that guide charges to the intended collection point while allowing compact integration of unrelated junctions nearby.
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 achieves high charge collection efficiency with minimal cross-talk and low photodiode capacitance, enhancing image sharpness and noise performance by ensuring that charge carriers are trapped within the intended pixel, rather than diffusing to neighboring pixels.
Implementation Method 1
All charges generated within the so-called diffusion length from the collecting junction have a chance of diffusing towards that junction
Implementation Method 2
The third region having dopants of the first conductivity type at a higher doping density than the substrate forms a barrier for substantially impeding the diffusion of carriers to the second region
Data Source
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AI summary
A semiconductor detector for particle or electromagnetic radiation comprises an epitaxial layer (1) having dopants of a first conductivity type. The detector also comprises a first region (2) and a second region (3) both having net dopants of a second conductivity type. The first region (2) is adapted for collecting charge carriers generated in the epitaxial layer (1) by the radiation and the second region (3) forms part of another junction of the detector. The detector further comprises a third region (4) having net dopants of the first conductivity type at a lower doping level than the epitaxial layer. The third region is positioned beneath the first and second regions (2), (3) and forms a charge-trapping region for collecting charge carriers generated in the epitaxial layer (1) and for channelling them towards the first region (2).