Grant: Strategic Projects - Group

NSERC strategic involves the preparation, fabrication and characterization of amorphous selenium (a-Se) based alloys for use in ultra high resolution direct conversion x-ray image detectors (image sensors), for small area imaging. In a recent NIH (USA) grant with Sunnybrook Hospital we were able to demonstrate a prototype high resolution a-Se/CCD based small area x-ray detector suitable for slot scanning mammography in which the resolution was limited by charge carrier trapping in a-Se. In previous strategic and CRD (with Anrad) grants we have shown the relationship between resolution and charge trapping in the photoconductor. If charge trapping in a-Se can be reduced (ideally, eliminated) there is no reason why a-Se/CCD detectors with pixel sizes as small as 3 micron cannot be made feasible for ultra high resolution x-ray imaging of small areas. Such ultra-high resolution real time imaging x-ray devices would be highly beneficial because they would enable low-cost imaging with low maintenance and the early detection of various forms of cancer or malignant growths. (Both the latter factors are within NSERC's strategic grant target "biomedical technologies"). Specifically we need to understand the factors that control the electron and hole lifetimes and how these critica quantities depend on the structure, preparation of the starting material (such as the quench temperature), alloying and dopants. We intent to use the Canadian Light Source at the university to carry out EXAFS and XANES studies of the structure of various doped a-Se alloys to obtain a better understating of their properties. The sponsoring company (Anrad) will provide the photoconductor source materials. Doping and alloying will be done at the U of S where we have extensive experience. We will also fabricate various a-Se photoconductor films as used in the actual detector. Interrupted field time-of-flight transient photoconductivity measurements and temperature modulated differential scanning calorimetric measurements will be used to electrically and thermally characterize the doped a-Se alloys. The synchrotron provides us with an excellent tool, and a unique opportunity, to improve a-Se alloys towards ultra-high resolution imaging.