Infra-red microscopy of Cd(Zn)Te radiation detectors revealing their internal electric field structure under bias

Antonis, P. De; Morton, Edward J.; Podd, Frank

doi:10.1109/23.507089

Cited by 47 publications

(19 citation statements)

References 2 publications

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“…However, the electric field appears to be nonuniform for CZT detectors under infrared (IR) light illumination with certain wavelengths. [2][3][4][5] Secondly, there is an urgency to improve the g-ray energy resolution, especially for large-volume (.1 cm 3 ) detectors and high-energy (. ;300 keV) g rays.…”

Section: Introductionmentioning

confidence: 99%

Characterization of Cd1−xZnxTe crystals grown from a modified vertical bridgman technique

Cui

Groza

Wright

et al. 2006

Journal of Elec Materi

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Cd 1ÿ x Zn x Te (CZT) crystals grown from a modified vertical Bridgman technique were characterized by means of an optical polarized transmission technique using the Pockels effect, low-temperature direct current (DC) photoconductivity technique, low-temperature photoluminescence (PL) spectroscopy, room-temperature PL mapping technique, and detector performance measurements. Electric field mapping indicates that an approximation of a uniform electric field distribution approximation is generally satisfied for CZT detectors operated at room temperature under typical working conditions. A nonuniform electric field distribution is observed under intense infrared (IR) light illumination, and a model is proposed based on charge generation of defects, trapping, and space-charge effects. The largest hole mobility-lifetime product (mt) h of the CZT detector measured by DC photoconductivity is 7.0 3 10 ÿ 4 cm 2 /V. The detector treated with 2% bromine in methanol chemical etch has a relatively small surface recombination velocity at room temperature, which was obtained from DC photocurrent and detector performance tests, as measured by irradiation of 5.5-MeV a particles and 59.6-keV g-rays, respectively. We have clearly shown the equivalence of charge collection efficiency results measured by both DC photocurrent and a particle response. Lowtemperature DC photocurrent measurements show that surface recombination velocity increases significantly with decreasing temperature from 300 K to 250 K. The effective electron mobility-lifetime product-combination effects of bulk and surface of CZT crystal-increases with increment of temperature. Room-temperature PL mapping measurements indicate uniformity of zinc concentration within CZT crystals. Low-temperature PL spectroscopy shows that the dominant emission peaks are excitons, which are bound to either shallow neutral donors (D 0 , X) or neutral acceptors (A 0 , X), depending on the temperature, concentration of donors and acceptors, and the incident light intensity. It was found that the luminescence of (D 0 , X) depends linearly on the incident laser intensity, while (A 0 , X) has a nonlinear dependence.

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Section: Introductionmentioning

confidence: 99%

Characterization of Cd1−xZnxTe crystals grown from a modified vertical bridgman technique

Cui

Groza

Wright

et al. 2006

Journal of Elec Materi

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“…1 we show the effect the presence of an oxide layer under one of the electrodes. The internal electric field was measured and mapped using infrared microscopy of the Pockels electro-optic effect [33]. In practice, both intentional and unintentional oxide layers on CZT surfaces can be encountered, and this fact indicates the need for taking into account the surface effects in future modeling and designing of devices.…”

Section: Detector Fabrication and Evaluationmentioning

confidence: 99%

“…1 The modification of the internal electric field when an oxide layer was intentionally placed partially under one of the electrodes. The photo was obtained utilizing the infrared microscopy of the Pockels effect [33]. Lighter areas indicate a stronger electric field.…”

Section: Detector Fabrication and Evaluationmentioning

confidence: 99%

Development of portable CdZnTe spectrometers for remote sensing of signatures from nuclear materials

Bürger

Groza

Cui

et al. 2005

phys. stat. sol. (c)

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Room temperature cadmium zinc telluride (CZT) gamma-ray spectrometers are being developed for a number for years for medical, space and national security applications where high sensitivity, low operating power and compactness are indispensable. The technology has matured now to the point where large volume (several cubic centimeters) and high energy resolution (approximately 1% at 660 eV) of gamma photons, are becoming available for their incorporation into portable systems for remote sensing of signatures from nuclear materials. The straightforward approach of utilizing a planar CZT device has been excluded due to the incomplete collection arising from the trapping of holes and causing broadening of spectral lines at energies above 80 keV, to unacceptable levels of performance. Solutions are being pursued by developing devices aimed at processing the signal produced primarily by electrons and practically insensitive to the contribution of holes, and recent progress has been made in the areas of material growth as well as electrode and electronics design. Present materials challenges are in the growth of CZT boules from which large, oriented single crystal pieces can be cut to fabricate such sizable detectors. Since virtually all the detector grade CZT boules consist of several grains, the cost of a large, single crystal section is still high. Co-planar detectors, capacitive Frisch-grid detectors and devices taking advantage of the small pixel effect, are configurations with a range of requirements in crystallinity and defect content and involve variable degrees of complexity in the fabrication, surface passivation and signal processing. These devices have been demonstrated by several research groups and will be discussed in terms of their sensitivity and availability.

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“…There have been reports of intensified electric field near the cathode, as seen by infrared imaging using the electro-optic effect [14], however the results are controversial due the possibility of photoionization of deep traps during the measurements [15].…”

Section: Hi Methods Of Computationmentioning

confidence: 99%

Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, spectrumplus and coplanar grid

Lee

James

1999

Journal of Elec Materi

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Device simulations of(1) the laterally-contacted-fipo~aI-nuc~em detector (LUND), (2) the SpectrumPlus, (3) and the coplanar grid made of CdO.gZM.ITe (CZT)were performed for 'S7CSirradiation by 662.15 keV gamma-rays. Realistic and controlled simulations of the gamma-ray interactions with the CZT material were done using the MCNP4B2 Monte Carlo program, and the detector responses were simulated using the Sandia three-dimensional multielectrode simulation program (SandTMSP).The simulations were done for the best and the worst expected carrier nobilities and lifetimes of currently commercially available CZT materiaIs for radiation detector applications-For the simulated unipolar devices, the active device volumes were relatively large and the ener~q resolutions were fairly good, but these performance characteristics were found to be very sensitive to the materials properties. The internal electric fields, the weighting potentials, and the charge induced efficiency maps were calculated to give insights into the operation of these devicesTbe snbmittd mannaoript h k authored by a contractor of i&e un~ed States Government under contiad. Accordingly the Lkited States Gov. emment retains a non. excl~i~, royalty-free license to publish or re. produce the published form of this contribution, or aIlow others to do SO, for United Statea Gov~~t ppeeea.,- L IntroductionTheunipol= mdiation detectors madeofsemi-insulating C&.gZm.lTe (CZT),2] have recently received much attention, due to their potential for improved gma-ray detection sensitivi~andenergy resolution [3][4][5][6]. Because theeIectron rnobilities are -20 times larger than the hole nobilities and because the electron lifetimes are at least -10 times longer than the hole lifetimes in these materials [7,8], these unipolar devices are designed to depend only on the electron's transport properties.However, because of the unknown variation in the starting detector materials, the high cost of materials and fabrication, and the relatively complex geometries and operating conditions that are characteristic of these unipolar detector designs, quantitative experimental determination of their active volume and energy resolution are typically extremely difilcult. And it is just as difficult to determine how robust these perfommnce to these difficult tasks is to use validated computer programs for the characteristics are with respect to the inevitable variation of the of the carrier transpofi properties.A solution simulation of these devices. A device simulation can give the total control of the device and materials parameters and, in addition, it can allow the examination of all device finctions. We have performed device simulations of three recendy deveIoped unipolar detectors made of Cc&.gZnO.lTe:(1) the laterally-contacted-unipolar-nuclear detector (LUND) [Ref. 3,41,(2) DISCLAIMERPortions of this document may be illegible in electronic image products.Images are produced from the best available original document.was used for realistic and controlled interaction of gamma...

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Infra-red microscopy of Cd(Zn)Te radiation detectors revealing their internal electric field structure under bias

Cited by 47 publications

References 2 publications

Characterization of Cd1−xZnxTe crystals grown from a modified vertical bridgman technique

Characterization of Cd1−xZnxTe crystals grown from a modified vertical bridgman technique

Development of portable CdZnTe spectrometers for remote sensing of signatures from nuclear materials

Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, spectrumplus and coplanar grid

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