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Title: High-Resolution X-ray Mapping of CdZnTe Detectors

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
929933
Report Number(s):
BNL-80527-2008-JA
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Nuclear Instruments and Methods A; Journal Volume: 579
Country of Publication:
United States
Language:
English
Subject:
national synchrotron light source

Citation Formats

Carini,G., Bolotnikov, A., Camarda, G., and James, R.. High-Resolution X-ray Mapping of CdZnTe Detectors. United States: N. p., 2007. Web. doi:10.1016/j.nima.2007.04.078.
Carini,G., Bolotnikov, A., Camarda, G., & James, R.. High-Resolution X-ray Mapping of CdZnTe Detectors. United States. doi:10.1016/j.nima.2007.04.078.
Carini,G., Bolotnikov, A., Camarda, G., and James, R.. Mon . "High-Resolution X-ray Mapping of CdZnTe Detectors". United States. doi:10.1016/j.nima.2007.04.078.
@article{osti_929933,
title = {High-Resolution X-ray Mapping of CdZnTe Detectors},
author = {Carini,G. and Bolotnikov, A. and Camarda, G. and James, R.},
abstractNote = {},
doi = {10.1016/j.nima.2007.04.078},
journal = {Nuclear Instruments and Methods A},
number = ,
volume = 579,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • The leakage current of CdTe detectors can be significantly reduced by processing detector crystals with p-i-n structures. Leakage currents of the order of several nA/mm{sup 2} are achieved at room temperature which compares well with the leakage current of commercially available CdZnTe detectors. The leakage current can be reduced further by cooling the detector to about {minus}30 C, where values of about pA/mm{sup 2} are achieved. These low values enable the use of low-noise, pulsed-optical feedback preamplifiers and higher bias voltages. High bias voltage is necessary for efficient charge collection which reduces spectrum background and peak tailing. Applying rise timemore » discrimination circuitry to the linear amplifier reduces the tailing effect even further, especially at higher radiation energies. The authors tested several 4 to 30-mm{sup 2}, 0.6 to 1-mm thick p-i-n structure CdTe detector crystals at {minus}20 to {minus}30 C with a low-noise pulsed-optical feedback preamplifier and rise-time discriminator, and at best obtained energy resolutions of 700 eV at the 59.5-keV line of {sup 241}Am, 1.2 keV at the 122-keV line of {sup 57}Co, and 2.5 keV at the 662-keV line of {sup 137}Cs. A similar p-i-n structure was processed on a 4-mm{sup 2} Cd{sub 0.9}Zn{sub 0.1}Te detector crystal in order to reduce its leakage current, and energy resolutions of 368 eV at the 5.9-keV line of {sup 55}Fe, 670 eV at the 59.5-keV line of {sup 241}Am, and 2.6 keV at the 662-keV line of {sup 137}Cs were obtained. However, the detector suffered from a charge collection problem yielding relatively high background under the peaks.« 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 towardsmore » the side 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 control of the concentration of Zn and its fluctuation in the high pressure Bridgman grown CdZnTe crystals is part of the characterization work on the ternary grown ingots grown in house. In order to reach both high sensitivity and high position resolution, the authors have developed a new system consisting of a X-ray generator, coupled to a focusing X-ray capillary, delivering intense beams in the micron scale, since the intensity gain is around a factor of 100 compared to conventional methods. The characteristic X-rays are measured through a high resolution CdZnTe detector (225 eV at 5.9 keV FWHM) cooledmore » by a Peltier system. The results of the investigations on different kinds of crystals will be discussed.« less
  • The spectroscopic analysis of X-ray magnetic circular dichroism (XMCD), which serves as strong and element-specific magnetic contrast in full-field magnetic transmission soft x-ray microscopy, is shown to provide information on the local distribution of spin (S) and orbital (L) magnetic moments down to a spatial resolution of 25 nm limited by the x-ray optics used in the x-ray microscope. The spatially resolved L/S ratio observed in a multilayered (Co 0.3 nm/Pt 0.5 nm) × 30 thin film exhibiting a strong perpendicular magnetic anisotropy decreases significantly in the vicinity of domain walls, indicating a non-uniform spin configuration in the vertical profile of a domainmore » wall across the thin film. Quantitative XMCD mapping with x-ray spectro-microscopy will become an important characterization tool for systems with topological or engineered magnetization inhomogeneities.« less