Field-Shaping Multi-Well Avalanche Detector for Amorphous Selenium
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Solution Overview
Problem
Conventional amorphous selenium radiation detectors face challenges with field hot-spots, low carrier mobility, and irreversible material breakdown due to high electric fields, limiting their practical implementation for direct conversion avalanche gain.
Innovation Solution
A field-shaping multi-well avalanche detector structure with insulated wells and controlled electric field distribution, using double-grid electrodes to create a semi-Gaussian field distribution and reduce peak electric fields at the metal-semiconductor interface, preventing field hot-spots and enabling stable avalanche multiplication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a separate localized avalanche multiplication region is implemented in amorphous selenium, then gain variation is minimized compared to bulk avalanche, but field hot-spots form where F exceeds 150 V/μm leading to irreversible material breakdown
Solution Approach 1:
The patent applies local quality by creating distinct regions with different electric field characteristics: a high-field avalanche multiplication region for gain and a low-field drift region for charge collection. The drift region maintains F < 150 V/μm to prevent breakdown while the avalanche region achieves F > 30 V/μm for multiplication, with each region optimized for its specific function.
Solution Approach 2:
The detector is segmented into functionally distinct regions: an avalanche multiplication region with field-shaping electrodes for gain generation, and a drift region for charge collection. This segmentation allows independent optimization of each region's electric field profile, enabling stable operation with uniform gain without material breakdown.
2Productivity
If the electric field is increased above 30 V/micron to improve conversion of a-Se, then conversion efficiency is improved, but reliable detector construction and operation becomes extremely challenging and virtually impractical
Solution Approach 1:
High electric field (>30 V/μm) is applied locally only in the avalanche multiplication region where it is needed for efficient charge generation, while the drift region maintains low field (<150 V/μm) for stable charge collection. This localized high-field approach achieves improved conversion efficiency without requiring the entire detector structure to withstand high fields, making construction and operation practical.
3Productivity
If a unipolar solid-state detector with Frisch grid is used, then avalanche gain is achieved, but the highest electric field develops at the interface between semiconductor and pixel electrode resulting in high dark current due to large charge injection and potentially irreversible detector damage
Solution Approach 1:
The patent creates a low-field drift region between the avalanche multiplication region and pixel electrode where F < 150 V/μm. This local quality modification prevents high field formation at the semiconductor-pixel electrode interface, thereby reducing dark current and charge injection while maintaining avalanche gain in the separate multiplication region.
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 allows for stable and continuous avalanche multiplication gain in amorphous selenium detectors, improving temporal and energy resolution, reducing dark current, and enabling practical direct conversion avalanche detectors with lower bias voltage requirements.
Implementation Method 1
amorphous selenium (a-Se) which was previously developed for photocopying machines, has been commercially revived as a direct x-ray photoconductor
Implementation Method 2
Avalanche multiplication in selenium can be used to increase the electric charge gain
Data Source
AI summary
A field shaping multi-well avalanche detector and method for fabrication thereof are disclosed. The field shaping multi-well avalanche detector provides stable avalanche multiplication gain in direct conversion amorphous selenium radiation detectors. The detector provides stable avalanche multiplication gain by eliminating field hot-spots using high-density avalanche wells with insulated wells and field-shaping within each well.