Charge Sharing and Charge Loss in High-Flux Capable Pixelated CdZnTe Detectors

Abstract

Cadmium zinc telluride (CdZnTe) detectors are known to suffer from polarization effects under high photon flux due to poor hole transport in the crystal material. This has led to the development of a high-flux capable CdZnTe material (HF-CdZnTe). Detectors with the HF-CdZnTe material have shown promising results at mitigating the onset of the polarization phenomenon, likely linked to improved crystal quality and hole carrier transport. Better hole transport will have an impact on charge collection, particularly in pixelated detector designs and thick sensors (>1 mm). In this paper, the presence of charge sharing and the magnitude of charge loss were calculated for a 2 mm thick pixelated HF-CdZnTe detector with 250 μm pixel pitch and 25 μm pixel gaps, bonded to the STFC HEXITEC ASIC. Results are compared with a CdTe detector as a reference point and supported with simulations from a Monte-Carlo detector model. Charge sharing events showed minimal charge loss in the HF-CdZnTe, resulting in a spectral resolution of 1.63 ± 0.08 keV Full Width at Half Maximum (FWHM) for bipixel charge sharing events at 59.5 keV. Depth of interaction effects were shown to influence charge loss in shared events. The performance is discussed in relation to the improved hole transport of HF-CdZnTe and comparison with simulated results provided evidence of a uniform electric field.

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

“…As is clearly shown in Figures 4 and 5, the energy deficit after CSA is less severe for the HF-CZT detectors. Recently, similar results were obtained by other researchers [29]; in particular, they measured less-incomplete charge collection after CSA in HF-CZT pixel detectors, in comparison with CdTe pixel detectors, attributing this to the better hole transport properties of the HF-CZT crystals than the CdTe ones. We believe that this difference is not dependent on the charge transport properties of the carriers but is strictly related to the characteristics of the electric field lines near the inter-pixel gaps.…”

“…Enhancements in hole charge transport properties are necessary to minimize the effects of radiation-induced polarization phenomena at high fluxes [23][24][25][26]. Recently, high-µ h τ h THM-CZT crystals (µ h τ h > 10 −4 cm 2 /V) are provided by Redlen for high-flux applications [27][28][29]. Therefore, high-µ h τ h CZT detectors (high-flux HF-CZT detectors) are typically used for high-flux measurements, while high-µ e τ e CZT materials (low flux LF-CZT) for thick electron-sensing detectors generally work at low flux conditions.…”

“…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].…”

“…In this work, we investigated the effects of charge losses near the inter-pixel gap in LF/HF-THM CZT pixel detectors. The detectors are fabricated on THM-CZT crystals recently produced by Redlen Technologies company (Canada), for both low-(LF-CZT) [19][20][21][22] and high-(HF-CZT) flux applications [27][28][29]. Measurements with uncollimated radiation sources and collimated synchrotron X-ray beams were performed on LF/HF-CZT pixel detectors characterized by the same crystal dimensions, electrical layout, bias voltage operation, and readout electronics.…”

Physical Properties of Candidate X-ray Detector Material Rb4Ag2BiBr9

“…4−6 CdZnTe detectors offer the superior energy resolution but suffer from the poor hole transport. 7 While TlBr is a promising compound semiconductor material, the TlBr detector performance degrades over time due to the charge polarization, which is caused by the bromide anion migration. 8 Recently, three-dimensional (3D) halide perovskites with the general chemical formula of ABX 3 (where A = Cs + , methylammonium (MA) or formamidinium (FA); B = Pb 2+ ; X = I − , Br − , Cl − ) have emerged as potential next-generation room-temperature X-ray detector materials due to a unique combination of their excellent charge carrier transport properties, suitable band gap energies (MAPbI 3 : 1.57 eV, FAPbI 3 : 1.48 eV, CsPbI 3 : 1.73 eV), 9 high semiconductor resistivity (>10 7 Ω•cm) for leakage current reduction, high average atomic number Z for photon attenuation, and low material cost due to their solution processability.…”