Photon counting performance of amorphous selenium and its dependence on detector structure

Area of Science:

• Medical Imaging
• Materials Science
• Detector Physics

Background:

• Photon counting detectors (PCDs) offer improved x-ray imaging but face challenges with high costs and performance limitations.
• Amorphous selenium (a-Se) presents a cost-effective alternative for PCDs, enabling large-area deposition.
• Existing a-Se detectors suffer from low carrier mobility and charge conversion gain, hindering their widespread adoption.

Purpose of the Study:

• To develop a novel direct conversion field-shaping multiwell avalanche detector (SWAD) utilizing amorphous selenium.
• To overcome the limitations of low carrier mobility and charge conversion gain in a-Se based PCDs.
• To investigate the impact of unipolar time differential (UTD) charge sensing and avalanche gain on detector performance.

Main Methods:

• Development of a SWAD with a dual-grid design, creating separate nonavalanche (bulk) and avalanche (well) regions.
• Implementation of unipolar time differential (UTD) charge sensing with tunable avalanche gain.
• Utilized a probability-based numerical simulation to model detector performance and analyze pulse height spectra (PHS).

Main Results:

• The SWAD design achieves depth-independent avalanche gain.
• Simulated PHS for 59.5 and 30 keV photons showed excellent agreement with prior experimental measurements.
• Significant improvement in energy resolution from 33 keV (planar detector) to $$ (SWAD).
• SWAD demonstrated a linear response approaching $$ .

Conclusions:

• The SWAD architecture effectively enhances the performance of a-Se based photon counting detectors.
• The developed numerical model accurately predicts detector performance, validating the simulation approach.
• SWAD shows significant potential for cost-effective, high-performance x-ray imaging applications.