Recently developed semiconducting HgI2 polymeric composite x-ray detectors are very promising for digital radiography and non-destructive testing. We present a new model that explains well the variation of the detector's sensitivity with applied bias and crystallite shape and size, based on charge transport between grain boundaries through the polymeric layer gaps. A previously published model, which was developed for a different polymer/semiconductor composite failed to account for many details of our experimental results. The new polymeric binder presented in the present paper showed non-linear dark current versus voltage dependence, and a higher sensitivity. At the low voltage range, it showed a higher sensitivity for a reduced grain size. The new model addresses the grain geometry as an important factor, and accounts well to most sensitivity characteristics of our detectors. The model excludes itself from a debate in the literature concerning specifics of charge transport mechanisms in composites containing electrically conducting particles. However, certain charge transport between neighbor crystallites is necessary in order to explain the experimental results.
|