Grant: Collaborative Research and Development Grants

This is the second phase of an ongoing collaborative research and development (CRD) program with Anrad that aims to enhance the properties of a-Se alloys, and aims to develop models for a-Se photoconductors used in recently commercialized a-Se based x-ray image detectors for medical imaging. Recent research has shown clearly that the one of the most promising digital radiographic systems is a flat panel sensor system that would directly replace the outdated film cassette technology in present day x-ray clinics. This system is based on using a large area TFT active matrix array panel with an electroded x-ray photoconductor. Although the a-Se based flat panel detector has been already commercialized, there are still a number of unsolved technological problems that must be overcome to enhance the detector performance. One of the most important enhancements that can be made is in the n-like a-Se layer that is used to reduce the dark current. We hope to use the CRD project to carry out the following research: (i) Examine the addition of IIA dopants to stabilized a-Se to extend the earlier work to see whether stable material can be synthesized at all. (ii) Measure the charge carrier ranges??drift mobility x lifetime) in n-type a-Se by the IFTOF (Interrupted Field time-of-flight) transient photoconductivity. (iii) Continue the experimental work on the relaxation of the properties of a-Se alloys to examine the relaxation of the properties of n-layers as well and layers with As greater than 0.2%. (iv) Measure the dark current in p-i-n, i-n and single layers as a function of time and applied nominal field. (v) Develop useful models for the dark current so that it can be predicted as a function of time and applied field from the intrinsic material properties; and examine its dependence on x-ray exposure.(vi) Examine the charge carrier and ghosting properties of a-Se layers as a function of exposure and temperature.Some of the alloys and films will be prepared at Anrad. During the tenure of the CRD grant we will concentrate our research efforts in these six areas in collaboration with Anrad. The proposed CRD grant builds on the expertise gained in the last phase and therefore starts from an already established know-how.