High-Resistance Semiconductor Structure for Avalanche Radiation Detector
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Solution Overview
Problem
Current semiconductor detectors with low-impedance substrates face challenges in producing larger pixel structures with better quantum yield and reduced 'after pulsing' due to geometric limitations and high capacitance, leading to inefficient detection and high yield losses.
Innovation Solution
A semiconductor structure with a high-resistance substrate and additional doping regions is used, allowing for precise setting of operating points and decoupling charge carrier depletion zones, enabling larger pixel geometries and improved quantum efficiency while reducing 'after pulsing' through a planar arrangement of doping zones and a cap layer forming a pn junction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low-impedance semiconductor substrates are used to ensure reliable functioning and suitable operating point, then the detector can operate in Geiger mode, but the device complexity increases and manufacturing precision requirements become very narrow due to the need for precise coordination of geometric dimensions and layer thickness
Solution Approach 1:
The patent changes the electrical parameter of the substrate from low-impedance to high-impedance (specific resistance of at least 500 ohm cm). This parameter change allows the detector to maintain reliable Geiger mode operation while significantly reducing the sensitivity to geometric dimensions and layer thickness variations, thereby reducing device complexity and manufacturing precision requirements.
Solution Approach 2:
Instead of using the conventional low-impedance substrate approach, the patent inverts the approach by using a high-impedance substrate. This inversion fundamentally changes the electrical characteristics of the detector, allowing it to achieve the desired operating point without the stringent geometric coordination requirements that plague low-impedance designs.
2Reliability
If low-impedance substrates are used, then the detector can function, but the pixel geometry is limited to very small sizes because only small layer thicknesses can be depleted before breakdown field strengths are reached
Solution Approach 1:
By changing the substrate impedance parameter from low to high (specific resistance ≥ 500 ohm cm), the patent enables the depletion of much thicker semiconductor layers without reaching breakdown field strengths. This allows pixel geometries to be scaled up from micrometer to millimeter dimensions while maintaining functional capability.
3Productivity
If small gap areas between pixels are designed to achieve good quantum yield, then detection efficiency improves, but after pulsing becomes a major problem due to photons traveling 7-8 micrometers before absorption and triggering adjacent pixels
Solution Approach 1:
The high-impedance substrate parameter enables the creation of sufficiently large gap areas between pixels that prevent cross-pixel triggering from after-pulsing photons, while still maintaining good quantum yield. The high impedance prevents the propagation of spurious signals that would otherwise cause adjacent pixels to fire.
4Ease of manufacture
If epitaxial layer thickness fluctuates from center to edge of wafer, then manufacturing variations occur, but with low-impedance substrates this leads to considerable yield losses due to the narrow technological window
Solution Approach 1:
By using a high-impedance substrate, the patent creates a much wider technological window that is insensitive to epitaxial layer thickness fluctuations. This allows standard manufacturing variations to be tolerated without causing device failure, thereby dramatically improving yield while maintaining ease of manufacture.
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 supports the production of larger pixel structures with enhanced quantum yield and reduced 'after pulsing', allowing for more precise operating point settings and improved detection efficiency by utilizing high-resistance substrates and additional doping regions to manage charge carrier depletion and avalanche effects effectively.
Implementation Method 1
Semiconductor detectors with a signal amplification by means of the avalanche effect are often used in radiation receivers for single-photon detection
Implementation Method 2
the depletion region of the first pn junction covers the open further region reaches a further range before the first pn junction breaks down
Data Source
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Figure 3
Figure 4~5
AI summary
The invention relates to a semiconductor structure for a radiation detector, comprising a substrate (12) made of a semiconductor material of a first conductivity type, a semiconductor substrate (14), wherein the semiconductor substrate (14) has a semiconductor layer arranged on the substrate (12) which has a higher resistance compared to the substrate (12) and is of the first conductivity type, doping regions (13), wherein the doping regions (13) are embedded in the semiconductor substrate (14) and are isolated from one another, and are of a second conductivity type, at least one further doping region (15), wherein the at least one further doping region (15) is embedded in the semiconductor substrate (14) and is associated with one or more of the doping regions, and is of the first conductivity type, and a cover layer (10) arranged on the semiconductor substrate (14) and of the second conductivity type.wherein an avalanche region is formed in the semiconductor substrate (14) between the doping regions (13, 15) arranged therein and the cover layer (10) arranged on the semiconductor substrate (14), in which a multiplication of free charge carriers takes place during operation due to collisions, and wherein an quenching region is formed in the semiconductor substrate (14) between the doping regions (13, 15) arranged therein and the substrate (12). The invention further relates to a radiation detector.