X-ray Detector Ohmic Contact Energy Matching
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Solution Overview
Problem
Direct-conversion semiconductor detectors in CT systems face limitations due to non-ideal ohmic contacts, leading to charge carrier accumulation and polarization, which restricts the detection of high radiation fluxes and results in inaccurate measurement results.
Innovation Solution
Achieving ideal ohmic contacts by selecting contact materials with excitation energies matching those of the semiconductor materials, such as iridium, palladium, and specific alloys or stack sequences, ensuring a deviation of no more than 100 meV, thereby preventing space charge formation and polarization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional contact materials (platinum or gold) are used, then electrical connection is achieved, but charge carrier accumulation and polarization occur due to non-ideal ohmic contacts
Solution Approach 1:
The patent changes the energy parameter (excitation energy) of the contact material to match the semiconductor material's excitation energy. This parameter matching eliminates the energy barrier at the interface, preventing charge carrier accumulation and space charge formation while maintaining reliable electrical connection.
Solution Approach 2:
The patent uses contact materials with excitation energies copied from or matching the semiconductor material's excitation energy (e.g., CdTe contact for CdTe semiconductor). This copying of the energy characteristic creates an ideal ohmic contact without the harmful space charge effects associated with conventional platinum or gold contacts.
2Measurement precision
If direct-conversion semiconductor detectors are used, then individual photon detection is enabled, but polarization limits the maximum detectable flux
Solution Approach 1:
The patent changes the contact material's excitation energy parameter to match the semiconductor material, eliminating the energy mismatch that causes charge carrier accumulation. This resolves the polarization effect that limits maximum detectable flux, enabling both precise photon detection and high flux measurement capability.
3Ease of manufacture
If non-matching contact materials are used, then manufacturing is simplified, but charge carrier separation and transport are impeded
Solution Approach 1:
The patent specifies a particular parameter relationship (matching excitation energies within 100 meV) that must be satisfied for ideal ohmic contact. This parameter matching ensures efficient charge carrier separation and transport while maintaining manufacturing feasibility through the selection of appropriate contact materials.
4Device complexity
If conventional contacts are used, then device structure is simple, but measurement results are inaccurate under high radiation density
Solution Approach 1:
The patent changes the energy parameter of the contact material to match the semiconductor material's excitation energy. This simple parameter change in material selection eliminates space charge formation and polarization effects, enabling accurate measurement results under high radiation density without complicating the device structure.
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
Enables precise measurement of high current flows and accurate detection of radiation fluxes, improving signal-to-noise ratio and measurement stability by minimizing charge carrier trapping in deep defects, and allowing for efficient conversion of radiation into electrical pulses.
Implementation Method 1
realize an ideal ohmic contact in a direct-conversion detector
Implementation Method 2
injection of holes occurs in the case of platinum contacts and injection of electrons occurs in the case of gold contacts
Implementation Method 3
the direct-conversion detectors based on semiconductor materials such as CdTe, CdZnTe, CdTeSe and CdZnTeSe, for example, are able to count individual photons, and hence detect the radiation directly
Implementation Method 4
the thermal excitation energy of the charge carriers, e.g. electrons, is 25 meV at room temperature. However, since this only corresponds to the average energy of the entire particles of an ensemble, a portion of the charge carriers of this ensemble consequently has a higher energy and, when thermally excited, can surmount this relatively small barrier
Implementation Method 5
These deep defects can trap the charge carriers generated by radiation and recombine with them
Implementation Method 6
The space charge therefore leads to an amplification of the effect of polarization. Polarization is understood to mean the reduction of the electric field by stationary charges that are generally bound to deep defects
Data Source
AI summary
At least one embodiment of the invention relates to an X-ray radiation detector, in particular for use in a CT system. In at least one embodiment, the X-ray radiation detector includes a semiconductor material used for detection, at least two ohmic contacts between the semiconductor material and a contact material, the semiconductor material and contact material each having a specific excitation energy of the charge carriers, with the excitation energy of the contact material corresponding to the excitation energy of the semiconductor material. At least one embodiment of the invention furthermore relates to a CT system in which an X-ray radiation detector is used, the X-ray radiation detector advantageously having at least two ideal ohmic contacts according to at least one embodiment of the invention.