Radiation Detector Semiconductor Layer Impurity Gradients
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Solution Overview
Problem
Radiation detection apparatuses with semiconductor layers separated into islands face issues of leakage paths leading to increased reverse dark current and decreased dynamic range due to residual charge, which existing solutions do not adequately address.
Innovation Solution
The apparatus includes a conversion element with a semiconductor layer positioned outside the electrodes, featuring impurity semiconductor layers and an intrinsic semiconductor layer, with specific resistance and length ratios defined to minimize residual charge and reverse dark current, ensuring the charge is less than 2% after the switching element is turned on.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the semiconductor layer is separated into islands for respective pixels, then a sharp image with less crosstalk between pixels is obtained, but a leakage path is readily formed on the side wall of the semiconductor layer causing increased reverse dark current
Solution Approach 1:
An insulating layer is introduced as an intermediary substance between the semiconductor layer and the surrounding environment. This insulating layer coats the side walls of the semiconductor layer islands, preventing the formation of leakage paths while maintaining the pixel separation benefits. The insulating layer acts as a mediator that blocks harmful electrical leakage without interfering with the intended pixel isolation for image sharpness.
2Object-generated harmful factors
If the periphery of a semiconductor layer is positioned outside the periphery of an electrode to suppress leakage path formation, then reverse dark current is reduced, but residual charge readily occurs
Solution Approach 1:
The invention changes the electrical parameters of the semiconductor layer by controlling impurity concentration distributions. By creating specific impurity concentration gradients in the semiconductor layer, the electrical characteristics are modified to reduce residual charge while maintaining the structural configuration that suppresses reverse dark current. This parameter adjustment allows the system to achieve both low reverse dark current and low residual charge.
Solution Approach 2:
Different regions of the semiconductor layer are given different impurity concentrations to create localized electrical properties. The semiconductor layer has higher impurity concentrations near the electrodes and lower concentrations in the bulk region, creating a gradient that optimizes both leakage suppression and residual charge reduction. This local quality variation allows simultaneous achievement of multiple performance goals.
3Reliability
If impurity concentration in the semiconductor layer is increased to reduce residual charge, then residual charge is reduced, but reverse dark current increases
Solution Approach 1:
The semiconductor layer is designed with spatially varying impurity concentrations, creating regions of high impurity concentration near the electrodes for low residual charge and regions of lower impurity concentration in the bulk for low reverse dark current. This local differentiation of electrical properties resolves the contradiction between reducing residual charge and maintaining low reverse dark current.
Solution Approach 2:
The impurity concentration parameter is changed as a function of position within the semiconductor layer. By creating a controlled gradient or distribution of impurity concentrations rather than a uniform value, the system optimizes both residual charge and reverse dark current characteristics simultaneously through parameter optimization.
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 residual charge and reverse dark current, allowing the apparatus to operate within desired parameters, maintaining image quality and dynamic range, and suppressing leakage currents.
Implementation Method 1
As the conversion element, a PIN diode or a MIS diode is used. In particular, a PIN structure in which a semiconductor layer is sandwiched between two electrodes can be easily manufactured
Implementation Method 2
a sheet resistance R□L1 of the first impurity semiconductor layer, a sheet resistance RU of the second impurity semiconductor layer
Data Source
AI summary
A radiation detection apparatus includes conversion elements including a first electrode, a semiconductor layer, and a second electrode that are divided for each pixel; switching elements electrically connected to the first electrodes; and a first insulating layer that separates the conversion elements of adjacent pixels. The semiconductor layer is located between the first and second electrodes. A periphery of the semiconductor layer is located outside peripheries of the first and second electrodes. The semiconductor layer includes a first impurity semiconductor layer, a second impurity semiconductor layer, and an intrinsic semiconductor layer located between the first and second impurity semiconductor layers. Parameters of the apparatus are defined to set a residual charge 10 μs after the switching element is turned on to be not higher than 2%.