Optimizing parylene and photoconductor thickness in indirect conversion amorphous selenium detectors.

Area of Science:

• Materials Science
• Medical Imaging Physics
• Semiconductor Device Physics

Background:

• Amorphous selenium (a-Se) is a cost-effective material for photodetectors in indirect conversion imaging.
• A-Se's wide bandgap limits sensitivity to longer wavelengths, such as the 550 nm light from CsI:Tl scintillators.
• Incorporating tellurium into a-Se (a-Se-Te) reduces the bandgap, enhancing sensitivity to longer wavelengths.

Purpose of the Study:

• To evaluate the impact of varying amorphous selenium-tellurium (a-Se-Te) and parylene layer thicknesses on photodetector performance.
• To optimize layer thicknesses for high sensitivity, low leakage, and minimal lag and ghosting in indirect conversion detectors.
• To understand the trade-offs between dark current and residual charge influenced by parylene layer thickness.

Main Methods:

• Fabrication and testing of single-pixel Se-Te photodetector devices with variable parylene and a-Se-Te layer thicknesses.
• Analysis of device performance metrics including dark current, signal levels, lag, and residual charge.
• Investigation of the role of the parylene layer as a hole blocking layer.

Main Results:

• Thicker a-Se-Te and parylene layers result in lower dark current, expected signal levels, and reduced lag.
• Thinner a-Se-Te and parylene layers lead to signal loss and residual charge accumulation.
• Parylene layer thickness influences a trade-off between dark current and residual charge.

Conclusions:

• Optimizing a-Se-Te and parylene layer thicknesses is crucial for achieving high-performance indirect conversion detectors.
• Thicker photoconductor and parylene layers are necessary for effective hole blocking and improved overall device performance.
• Further optimization is required to balance dark current and residual charge for advanced imaging applications.