Modelling Polarization Effects in a CdZnTe Sensor at Low Bias

Area of Science:

• Materials Science
• Solid-State Physics
• Radiation Detection

Background:

• Semi-insulating Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) pixelated sensors are crucial for photon-counting applications like medical computed tomography (CT), airport scanners, and non-destructive testing (NDT).
• These applications often involve rapidly changing and high-flux X-ray irradiation environments, posing significant operational challenges for detector performance and stability.

Purpose of the Study:

• To investigate the operational feasibility of CdTe and CdZnTe detectors under high-flux X-ray irradiation using a low electric field.
• To numerically simulate and analyze electric field profiles, polarization effects, and charge transport phenomena in these detectors.
• To evaluate the impact of detector electronics on spectral quality and propose optimization strategies for spectral CT applications.

Main Methods:

• Numerical simulation of coupled drift-diffusion and Poisson's equations to model electric field profiles and charge transport.
• Pockels effect measurements to visualize electric field profiles under high-flux polarization.
• Defect model development to consistently depict polarization phenomena.
• Simulation of X-ray spectrum construction on a 2-mm-thick pixelated CdZnTe detector (330 µm pixel pitch).

Main Results:

• The study successfully simulated detector performance under high-flux X-ray irradiation with a low electric field, demonstrating satisfactory counting operation.
• The numerical model accurately depicted polarization effects caused by high flux, correlating with Pockels effect measurements.
• Analysis revealed the influence of allied electronics on spectral quality, with simulated optimization strategies showing potential for improvement.

Conclusions:

• Pixelated CdTe and CdZnTe detectors are viable for high-flux X-ray applications requiring stable counting performance.
• Numerical simulations provide valuable insights into detector physics, enabling the prediction and mitigation of performance limitations like polarization.
• Optimization of detector setup and associated electronics is key to enhancing spectral resolution and overall performance in spectral CT systems.