Spectroscopy on thick HgI₂ detectors: a comparison between planar and pixelated electrodes

Thick mercuric iodide (HgI₂) detectors are investigated as potential room temperature gamma-ray spectrometers. By using pixelated anodes the induced charge on the electrode is dependent mainly on electron movement and is almost independent of the depth of interaction. Moreover, by reading out the planar cathode signal simultaneously, the depth of interaction can be determined and any effects of electron charge loss can be corrected. By combining these two methods (pixelated anodes and depth sensing), the resolution from 1 cm thick HgI₂ devices can be improved to 1.4% FWHM when using a Cs-137 point source. These results were obtained using a modest electric field (2500 V/cm) and relatively short shaping times (4-16 μs) for HgI₂. A comparison between conventional planar readout and single polarity charge sensing techniques with wide band-gap semiconductors is discussed.