Semiconductor Radiation Detector Infrared Hole Mobility
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Solution Overview
Problem
Ionizing radiation detectors, such as those used in medical imaging, face polarization issues due to the formation of positive space charge, which degrades their performance by reducing the internal electrical field and attracting electrons towards the cathode, especially under high flux conditions, leading to incomplete charge collection and poor energy resolution.
Innovation Solution
The method involves optically coupling infrared radiation into semiconductor radiation detectors to convert heavy holes into lighter holes or spin-orbit holes, increasing their mobility and reducing polarization effects by exciting holes from one valence energy band to another with lower effective masses, thereby improving hole collection and detector performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If detectors are operated at high bias voltage to improve hole drift velocity, then detector performance is improved, but leakage current increases
Solution Approach 1:
The patent applies parameter changes by using infrared radiation to alter the effective mass of holes, transitioning them from heavy-hole bands to light-hole bands. This changes the fundamental parameter of hole mass, enabling faster drift velocity without increasing bias voltage, thus avoiding increased leakage current.
2Speed
If detectors are made thinner to improve hole collection, then detector performance is improved, but stopping power is reduced
Solution Approach 1:
The patent changes the mass parameter of holes through infrared irradiation, enabling them to move faster and be collected more efficiently in thicker detectors. This allows the use of thicker detector materials that provide adequate stopping power while still achieving good hole collection through the enhanced mobility of light-hole-band carriers.
3Productivity
If high flux of ionizing radiation is used to improve imaging speed, then productivity is improved, but polarization effect increases
Solution Approach 1:
The patent changes the effective mass parameter of holes by exciting them to the light-hole band using infrared radiation. This parameter change enables holes to drift faster toward the cathode even under high flux conditions, preventing space charge accumulation and reducing polarization effects that would otherwise limit imaging speed.
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 enhances image quality, reduces polarization, and allows for better contrast and lower dose imaging while eliminating 'after-glow' artifacts, enabling the use of radiation detectors in multiple imaging modalities with improved energy resolution and reduced low energy tails.
Implementation Method 1
The IR radiation has at least one wavelength selected from a spectral range including wavelengths to which the semiconductor plate is partially transparent and which are configured to excite at least some of the holes from a first group at a first valence energy band to a second group at a second valence energy band
Implementation Method 2
each ionizing photon absorbed in the detector may create an electron-cloud and a holes-cloud
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A method 100 is provided including acquiring 506 detection events with a radiation detector 600 including a semiconductor plate 610 and configured to produce electrical signals in response to absorption of ionizing radiation in the semiconductor plate 610, wherein electrons and holes are generated responsive to absorption of the ionizing radiation. The semiconductor plate 610 includes a first surface 611 opposed to a second surface 613, with sidewalls 616 interposed between the first surface 611 and the second surface 613. A cathode electrode 612 is disposed on the first surface 611 and pixelated anode electrodes 614 are disposed on the second surface 613. The method 100 also includes optically coupling 508 infrared IR radiation into a first portion 650 of at least one of the sidewalls 616 of the semiconductor plate 610 of the radiation detector 600, and not coupling IR radiation into a second portion 652 of the at least one of the sidewalls 616.