Charge Collection I.N A Se Photoconductor on a Thin Film Transistor Array during X-Ray Imaging

Abstract

ABSTRACTThis paper deals with performance aspects of a selenium photoconductor on a thin film transistor array when used in x-ray imaging, e.g. for medical applications. We present the effects of doping structures within the Se on the spatial resolution, temporal response and dark current characteristics. Measurements were done on a 1922 pixel array with 200 μm pitch and a collecting electrode covering 50 % of the pixel area. Without additional measures the detector has a prohibitively slow response. With properly chosen doping structures the lateral conductivity can be engineered in a manner that the speed of the Se-TFT detector is increased to a level acceptable for video rate imaging. There is also a critical relationship between doping structures in the photoconductor and the spatial resolution of the detector. An idea of how these doping structures work in terms of resolution and speed of the detector is presented, together with proposals for an optimized doping scheme.