Abstract
Amorphous selenium (a-Se) is a photoconductive material that has been intensively investigated from its early application in xerography to its present application in flat panel X-ray imagers. It can be deposited up to a few millimeters thick over a large area. Its high vapor pressure yields uniform coverage in novel device structures for low-cost and large-area applications. The evidence of avalanche multiplication in a-Se and application of a-Se in high-gain avalanche rushing photoconductor video-tubes goes back to the early 1980s. Over the past decade there has been increasing research interest in novel detector structures and integration of a-Se with new materials to leverage the avalanche properties. We summarize some of the shortcomings of a-Se such as low charge carrier mobility, low charge conversion efficiency, depth dependence, and high dark current at high electric fields. We then highlight recent developments in a-Se-based devices to address these shortcomings and enable picosecond timing performance and high detection efficiency.
Highlights
A MORPHOUS selenium has a low melting point and high vapor pressure which makes it less complex and more economical to deposit thick and uniform layers over a large area by for example thermal evaporation
Amorphous selenium (a-Se) has good X-ray photoconductivity, discovered in the 1940s, and can be used in X-ray imaging. amorphous selenium (a-Se) was heavily used in the photocopy industry until it was replaced by inexpensive organic photoconductors in the late 1980s [1]
With a strong electric field applied (10 V/μm or higher) [9], a-Se exhibits excellent X-ray photoconductivity, especially in the energy range used for Manuscript received September 7, 2019; revised October 26, 2019; accepted October 26, 2019
Summary
A MORPHOUS selenium has a low melting point and high vapor pressure which makes it less complex and more economical to deposit thick and uniform layers over a large area by for example thermal evaporation. Besides this advantage, amorphous selenium (a-Se) has good X-ray photoconductivity, discovered in the 1940s, and can be used in X-ray imaging. But not least, a-Se direct detectors have been proven to have superior spatial resolution [23] These advantages have kept researchers working to develop better a-Se-based X-ray imagers. The discovery of new materials, and the refinement of manufacturing techniques, many detectors with superior properties have been developed
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