Progress in Lead OxideX‐Ray Photoconductive Layers

X-ray imaging detectors rely on either indirect or direct conversion of X-ray quanta to an electrical signal. Most commonly used in commercial systems, the indirect scheme involves a multistage conversion process that begins with a scintillator converting X-ray quanta into optical photons. The optical photons in turn diffuse through a phosphor and then are converted to electrons by an array of photodiodes. In the direct method, the X-ray quanta are absorbed in a photoconductor that directly creates electron–hole pairs. The electrons and holes are then separated by a bias electric field to generate an electrical signal in the imaging array. With the right photoconductor, the direct conversion scheme offers a high spatial resolution, limited only by the pixel size of the imaging array, and improved dose efficiency down to the lowest required radiation exposure. Here we present the results of materials science research into new X-ray photoconductive structures based on two different polymorphs of lead oxide (PbO) photoconductors for application in direct conversion X-ray detectors, namely, polycrystalline lead oxide ( poly-PbO ) and amorphous lead oxide ( a-PbO ). Optimization of PbO technology was focused on improving the collection of the X-ray–generated charge and solving the problem of signal lag, that is, the residual signal after the end of X-ray exposure. The latter is one of the main obstacles to the use of disordered semiconductors as X-ray-to-charge transducers since the presence of signal lag limits the application of direct conversion detectors to static imaging only and obscures the full potential of this detection method in diagnostic imaging. The approaches we have taken to improve the X-ray performance of PbO-based photoconductive structures can be applied to other promising materials to solve the problems common to disordered photoconductors, paving a way for their use in practical detectors.