Enhanced detection efficiency of direct conversion X-ray detector using polyimide as hole-blocking layer.

Area of Science:

• Medical Physics
• Materials Science
• Semiconductor Devices

Background:

• Direct conversion X-ray detectors utilize amorphous selenium (a-Se) for efficient X-ray to charge conversion.
• Optimizing detector performance requires managing charge carrier transport and minimizing leakage currents.

Purpose of the Study:

• To evaluate the performance enhancement of a-Se X-ray detectors using a novel polyimide (PI) hole-blocking layer.
• To investigate the impact of the PI layer on detector operation at high electric fields and assess charge carrier dynamics.

Main Methods:

• Fabrication of a-Se detectors incorporating a biphenyldisnhydride/1,4 phenylenediamine (BPDA/PPD) PI hole-blocking layer.
• Time-of-flight (TOF) measurements to determine hole mobility under varying electric fields.
• Characterization of detector performance including dark current, transient response, and avalanche multiplication.

Main Results:

• The PI/a-Se device operated effectively at high electric fields (≥10 V/μm) with low dark current and stable transient performance.
• Hole mobility reached up to 0.75 cm²/Vs in the PI/a-Se structure, significantly enhanced by increasing electric fields.
• Avalanche multiplication was demonstrated, and increasing electric fields within a-Se reduced ionization energy, boosting dynamic range and sensitivity.

Conclusions:

• The PI hole-blocking layer is crucial for high-performance a-Se X-ray detectors.
• The enhanced hole mobility and achievable avalanche multiplication indicate significant improvements in detector sensitivity and dynamic range.
• This technology holds promise for advanced X-ray imaging applications requiring high sensitivity and resolution.