Using ambipolar sensitivity in pixelated semiconductor detectors

Abstract

Significant hole motion has previously been observed in thick pixelated semiconductor detectors such as TlBr. This has been shown to affect depth reconstructions when using simple cathode-to-anode amplitude ratios by altering planar-cathode signals. In this work, a complementary effect altering pixelated-anode signals from a TlBr detector was observed. This effect increases the radiation-sensitive volume of a detector to include the region near the pixelated electrodes. A new depth analog based on the hole-induced pixel signal is introduced for near-pixel events. Applying an additional calibration with this new parameter improved the FWHM at 662 keV of a TlBr detector by 3–4 keV during room-temperature operation. The analysis and techniques are generalizable to ambipolar-sensitive pixelated detectors whose dominant charge carriers are either electrons or holes, allowing extension to promising hole-dominant semiconductors.