Recent Developments of Amorphous Selenium-Based X-Ray Detectors: A Review

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.