NSF Award
9261557
New techniques for digital X-ray imaging have been under investigation for decades. Some of the most promising techniques incorporate solid-state X-ray detectors, which are attractive because of their compactness. High-Z semiconductor X-ray detectors have further advantages due to their high stopping power. One of the drawbacks of high-Z semiconductor detectors was the cost of producing large-area arrays. The usual approach was to assemble an array of isolated, individually-fabricated detector elements. A competing technology is to enhance large area arrays of amorphous silicon (a-Si) photodiodes by coating them with a film of high-Z scintillating material (e.g. CsI) by evaporation. While this technique is more effective in stopping X-rays than using "naked" silicon photodiodes, the poor conversion efficiency of scintillators limits the signal amplitude. We propose producing sublimed films of a new, high-Z semiconductor (thallium bromide), and to characterize their utility as pixilated detectors for X-ray image detection. We have made measurements of sublimed TlBr films produced in our laboratories and have noted that these detectors maintain surprisingly good charge carrier transport properties in spite of their poor crystallinity. We propose that these films will be read out by depositing them on an amorphous silicon thin-film transistor array. These detectors would yield a larger signal than the scintillator-enhanced detectors, due to their high conversion efficiency while maintaining high X-ray stopping power.
