Energy Recovery of Multiple Charge Sharing Events in Room Temperature Semiconductor Pixel Detectors

Abstract

Multiple coincidence events from charge-sharing and fluorescent cross-talk are typical drawbacks in room-temperature semiconductor pixel detectors. The mitigation of these distortions in the measured energy spectra, using charge-sharing discrimination (CSD) and charge-sharing addition (CSA) techniques, is always a trade-off between counting efficiency and energy resolution. The energy recovery of multiple coincidence events is still challenging due to the presence of charge losses after CSA. In this work, we will present original techniques able to correct charge losses after CSA even when multiple pixels are involved. Sub-millimeter cadmium–zinc–telluride (CdZnTe or CZT) pixel detectors were investigated with both uncollimated radiation sources and collimated synchrotron X rays, at energies below and above the K-shell absorption energy of the CZT material. These activities are in the framework of an international collaboration on the development of energy-resolved photon counting (ERPC) systems for spectroscopic X-ray imaging up to 150 keV.

Window-Based Energy Selecting X-ray Imaging and Charge Sharing in Cadmium Zinc Telluride Linear Array Detectors for Contaminant Detection

“…As is well documented in the literature [ 30 , 31 , 32 , 33 , 34 ], the charge sharing events, rejected by CSD, can be recovered in counting and energy through the application of the charge sharing addition (CSA) technique. This technique consists in a simple addition of the energy of the charge sharing events.…”

“…This technique consists in a simple addition of the energy of the charge sharing events. Unfortunately, the summed energy is often characterized by deficits due to incomplete charge collection effects at the inter-pixel gap [ 30 , 31 , 32 , 33 , 34 ]. These energy deficits were also observed in our measurements, as shown in Figure 12 .…”

Incomplete Charge Collection at Inter-Pixel Gap in Low- and High-Flux Cadmium Zinc Telluride Pixel Detectors

“…The detectors are based on THM-CZT crystals provided by Redlen and characterized by gold electro-less contacts. Recently, very-low-noise gold contacts were realized on CZT detectors by our group [19,[35][36][37][38]41], ensuring low leakage currents at room temperature (4.7 nA cm −2 at 1000 V cm −1 ) and good room-temperature operation even at high bias voltages (> 5000 V cm −1 ). The LF-CZT detectors are characterized by µ e τ e ranging from 1 to 3 × 10 −2 cm 2 /V and µ h τ h from 2 to 3 × 10 −5 cm 2 /V [27].…”

“…The cause of these distortions is unclear but may be due to either the presence of crystalline defects (inclusions) or perhaps issues with the electrical contacts. Fortunately, the energy deficits of the shared events after CSA can be recovered through a custom correction technique, recently developed by our group [36,37]. This technique is based on the correction of (i) the shared events after CSA with m = 2, (ii) the events with m > 2, and (iii) the fluorescence crosstalk events.…”

“…As is well known, the most important critical issues in sub-millimeter CZT pixel detectors are represented by charge-sharing and crosstalk effects, with the presence of severe degradations in both the spectral and spatial performance [29][30][31][32][33][34][35][36][37][38][39][40]. Despite the potential of charge-sharing addition (CSA) techniques in reducing the charge-sharing effects, the presence of incomplete charge collection in the summed energy after CSA often prevents full energy recovery in the energy spectra [33][34][35][36][37][38][39][40]. These effects, due to the presence of charge losses at the inter-pixel gaps, are strictly related to the physical properties of the detectors (crystals and electrical contacts) near the gaps between the pixels.…”