Comparative study of Pbl 2 and Hgl 2 as direct detector materials for high-resolution x-ray image sensors

Abstract

X-ray imaging properties are reported for HgI<SUB>2</SUB> and PbI<SUB>2</SUB>, as candidate materials for future direct detection x- ray image sensors, including the first results from screen- printed HgI<SUB>2</SUB> arrays. The leakage current of PbI<SUB>2</SUB> is reduced by using new deposition conditions, but is still larger than HgI<SUB>2</SUB>. Both HgI<SUB>2</SUB> and PbI<SUB>2</SUB> have high spatial resolution but new data shows that the residual image spreading of PbI<SUB>2</SUB> is not due to k-edge fluorescence and its possible origin is discussed. HgI<SUB>2</SUB> has substantially higher sensitivity than PbI<SUB>2</SUB> at comparable bias voltages, and we discuss the various loss mechanisms. Unlike PbI<SUB>2</SUB>, HgI<SUB>2</SUB> shows a substantial spatially non-uniform response that is believed to originate from the large grain size, which is comparable to the pixel size. We obtain zero spatial frequency DQE values of 0.7 - 0.8 with PbI(subscript 24/ under low energy exposure conditions. A model for signal generation in terms of the semiconducting properties of the materials is presented.