P-Type CZT Detector Doping for High-Flux Polarization Resistance
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Solution Overview
Problem
Photon counting X-ray computed tomography (CT) imaging systems experience performance loss due to electrical polarization during high-flux applications, which affects the detector's ability to accurately count X-ray photons at high flux rates.
Innovation Solution
An ionizing radiation detector with a p-type semiconductor single crystal substrate doped with n-type dopant atoms, where the concentration of deep level acceptor defects exceeds that of n-type dopant atoms, preventing detector polarization by maintaining a stable electric field under high X-ray flux conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional charge sensitive amplifier systems are used for photon counting X-ray CT, then the system can operate at standard flux rates, but performance is lost during high-flux applications due to electrical polarization
Solution Approach 1:
The patent changes the electrical parameters of the detector by introducing a p-type layer with specific hole concentration (10^16 to 10^18 cm^-3) and controlling the doping concentration (10^14 to 10^16 cm^-3). This parameter modification enables the detector to maintain stable performance under high-flux conditions by preventing charge accumulation that causes polarization.
Solution Approach 2:
The patent creates a composite semiconductor structure by combining n-type CZT material with a p-type layer. This composite structure leverages the complementary properties of both material types: the n-type material provides good charge transport while the p-type layer with controlled doping prevents polarization, achieving both high flux handling and performance stability.
2Productivity
If the detector is designed to handle high X-ray flux rates, then productivity increases, but electrical polarization occurs causing loss of measurement precision
Solution Approach 1:
The patent modifies the electrical parameters of the detector by introducing a p-type layer with specific hole concentration (10^16 to 10^18 cm^-3) and controlling the doping concentration (10^14 to 10^16 cm^-3). This parameter modification enables the detector to maintain stable performance under high-flux conditions by preventing charge accumulation that causes polarization.
Solution Approach 2:
The patent converts the potentially harmful effect of high flux-induced charge accumulation into a beneficial effect by using the p-type layer to attract and neutralize excess charges. The high flux that would normally cause polarization is instead managed by the p-type material, allowing accurate photon counting even at high counting rates.
3Ease of manufacture
If conventional n-type doped CZT substrates are used, then manufacturing is straightforward, but the detector experiences polarization under high-flux conditions
Solution Approach 1:
The patent creates a composite semiconductor structure by combining n-type CZT material with a p-type layer. This composite structure leverages the complementary properties of both material types: the n-type material provides good charge transport while the p-type layer with controlled doping prevents polarization, achieving both high flux handling and performance stability.
Solution Approach 2:
The patent applies local quality modification by introducing a p-type layer with specific properties (hole concentration 10^16 to 10^18 cm^-3) at a specific location within the detector structure. This localized modification with controlled doping concentration (10^14 to 10^16 cm^-3) provides polarization resistance exactly where needed without compromising the overall detector performance or manufacturing feasibility.
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
The detector operates effectively at high X-ray flux rates without experiencing polarization, ensuring accurate photon counting and maintaining performance across a wide range of X-ray flux conditions.
Implementation Method 1
a concentration of deep level acceptor defects is greater than a concentration of the n-type dopant atoms in the p-type semiconductor single crystal substrate
Implementation Method 2
the charge cloud resulting from an X-ray photon impinging on a sensor is converted to an amplified voltage
Data Source
AI summary
An ionizing radiation detector includes a p-type semiconductor single crystal substrate having first and second major planar opposing surfaces, where the p-type semiconductor single crystal substrate is doped with n-type dopant atoms, and where a concentration of deep level acceptor defects is greater than a concentration of the n-type dopant atoms in the p-type semiconductor single crystal substrate; a cathode electrode on the first major planar opposing surface of the p-type semiconductor single crystal substrate, and a plurality of anode electrodes on the second major planar opposing surface of the p-type semiconductor single crystal substrate.