Experimental investigation of direct-indirect flat-panel imager using tellurium doped amorphous selenium

Active matrix flat panel imagers (AMFPIs) are widely used in digital radiography, but direct and indirect conversion technologies each have limitations. Direct conversion detectors suffer from low x-ray quantum efficiency, while indirect conversion detectors experience spatial resolution degradation due to optical photon scatter. A direct-indirect “Hybrid” AMFPI, which combines both technologies, has previously shown potential to address these limitations. This hybrid design includes an amorphous selenium (a-Se) layer in contact with a scintillator, functioning as both an x-ray and optical sensor. This study builds on the first Hybrid AMFPI prototype, aiming to improve its detective quantum efficiency (DQE). Two key enhancements were explored: (1) increasing the a-Se layer thickness and (2) improving optical quantum efficiency (OQE) through tellurium (Te) doping. A 6.5 x 6.5 cm² prototype was fabricated with 700 µm a-Se, a Te-doped a-Se optical sensing layer, and a removable 1000 µm CsI:Tl scintillator. The Hybrid configuration showed a 42% (RQA5) and 91% (RQA9) increase in x-ray sensitivity compared to the direct AMFPI, attributed to an approximate tenfold improvement in OQE due to Te doping. The Hybrid achieved a DQE(0) of 0.90 (RQA5) and 0.75 (RQA9), marking it the highest-performing imager for digital radiography applications at RQA9. Preliminary real-time imaging (i.e., 30 frames-per-second) temporal performance measurements indicated minimal ghosting (below 2%) but up to 12% lag, attributed to electron trapping in the Te-doped layer. Future research will explore co-doping with arsenic to enhance electron transport to allow for real-time imaging.