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Title: Correlation between Electrical Field Distribution and Defect levels of CdZnTe Radiation Detectors

Authors:
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
OSTI Identifier:
1376084
Report Number(s):
BNL-113827-2017-CP
DOE Contract Number:
SC00112704
Resource Type:
Conference
Resource Relation:
Conference: 2017 SPIE Optics+Optoelectronics; Prague, Czech Republic; 20170424 through 20170427
Country of Publication:
United States
Language:
English
Subject:
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL PROTECTION

Citation Formats

Yang G. Correlation between Electrical Field Distribution and Defect levels of CdZnTe Radiation Detectors. United States: N. p., 2017. Web.
Yang G. Correlation between Electrical Field Distribution and Defect levels of CdZnTe Radiation Detectors. United States.
Yang G. 2017. "Correlation between Electrical Field Distribution and Defect levels of CdZnTe Radiation Detectors". United States. doi:. https://www.osti.gov/servlets/purl/1376084.
@article{osti_1376084,
title = {Correlation between Electrical Field Distribution and Defect levels of CdZnTe Radiation Detectors},
author = {Yang G.},
abstractNote = {},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = 2017,
month = 4
}

Conference:
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  • The ideal operation of CdZnTe devices entails having a uniformly distributed internal electric field. Such uniformity especially is critical for thick long-drift-length detectors, such as large-volume CPG and 3-D multi-pixel devices. Using a high-spatial resolution X-ray mapping technique, we investigated the distribution of the electric field in real devices. Our measurements demonstrate that in thin detectors, <5 mm, the electric field-lines tend to bend away from the side surfaces (i.e., a focusing effect). In thick detectors, 21 cm, with a large aspect ratio (thickness-to-width ratio), we observed two effects: the electric field lines bending away from or towards the sidemore » surfaces, which we called, respectively, the focusing field-line distribution and the defocusing field-line distribution. In addition to these large-scale variations, the field-line distributions were locally perturbed by the presence of extended defects and residual strains existing inside the crystals. We present our data clearly demonstrating the non-uniformity of the internal electric field.« less
  • The ideal operation of CdZnTe devices entails having a uniformly distributed internal electric field. Such uniformity especially is critical for thick long-drift-length detectors, such as large-volume CPG and 3-D multi-pixel devices. Using a high-spatial resolution X-ray mapping technique, we investigated the distribution of the electric field in real devices. Our measurements demonstrate that in thin detectors, <5 mm, the electric field-lines tend to bend away from the side surfaces (i.e., a focusing effect). In thick detectors, >1 cm, with a large aspect ratio (thickness-to-width ratio), we observed two effects: the electric field lines bending away from or towards the sidemore » surfaces, which we called, respectively, the focusing field-line distribution and the defocusing field-line distribution. In addition to these large-scale variations, the field-line distributions were locally perturbed by the presence of extended defects and residual strains existing inside the crystals. We present our data clearly demonstrating the non-uniformity of the internal electric field.« less
  • In this work we measured the crystal defect levels and tested the performance of CdZnTe detectors by diverse methodologies, viz., Current Deep Level Transient Spectroscopy (I-DLTS), Transient Current Technique (TCT), Current and Capacitance versus Voltage measurements (I-V and C-V), and gamma-ray spectroscopy. Two important characteristics of I-DLTS technique for advancing this research are (1) it is applicable for high-resistivity materials (>10{sup 6} {Omega}-cm), and, (2) the minimum temperature for measurements can be as low as 10 K. Such low-temperature capability is excellent for obtaining measurements at shallow levels. We acquired CdZnTe crystals grown by different techniques from two different vendorsmore » and characterized them for point defects and their response to photons. I-DLTS studies encompassed measuring the parameters of the defects, such as the energy levels in the band gap, the carrier capture cross-sections and their densities. The current induced by the laser-generated carriers and the charge collected (or number of electrons collected) were obtained using TCT that also provides the transport properties, such as the carrier life time and mobility of the detectors under study. The detector's electrical characteristics were explored, and its performance tested using I-V, C-V and gamma-ray spectroscopy.« less
  • Homogeneity of properties related to material crystallinity is a critical parameter for achieving high-performance CdZnTe (CZT) radiation detectors. Unfortunately, this requirement is not always satisfied in today's commercial CZT material due to high concentrations of extended defects, in particular subgrain boundaries, which are believed to be part of the causes hampering the energy resolution and efficiency of CZT detectors. In the past, the effects of subgrain boundaries have been studied in Si, Ge and other semiconductors. It was demonstrated that subgrain boundaries tend to accumulate secondary phases and impurities causing inhomogeneous distributions of trapping centers. It was also demonstrated thatmore » subgrain boundaries result in local perturbations of the electric field, which affect the carrier transport and other properties of semiconductor devices. The subgrain boundaries in CZT material likely behave in a similar way, which makes them responsible for variations in the electron drift time and carrier trapping in CZT detectors. In this work, we employed the transient current technique to measure variations in the electron drift time and related the variations to the device performances and subgrain boundaries, whose presence in the crystals were confirmed with white beam X-ray diffraction topography and infrared transmission microscopy.« less