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1.
The charge collection efficiency of CdZnTe radiation detectors with two different configurations: aSchottky diode detector and aresistive detector are compared. The average charge collection efficiencies for three different directions of irradiation (negative electrode,
positive electrode and perpendicular to the electric field) are calculated. The mobility-lifetime product of the CdZnTe substrates
is evaluated from the dependence of the measured spectra upon detector bias voltage. The measurement of the average charge
collection efficiency is based on monitoring the shift of the peak channel with bias voltage in an experimental setup which
is well calibrated. Two types of radiation are used:gamma photons from several radioactive sources andalpha particles from an241Am source. The models for the evaluation of mobility-lifetime product from the measured data for the two types of detector
configurations as well as for the two types of radiation sources, are compared and discussed. The CdZnTe (Zn = 10%) substrates
under study are obtained commercially and are grown by the high pressure Bridgeman method. The mobility-lifetime products
and specific resistivity of the two types of detectors are evaluated and compared. A lower resistivity material has a narrower
depletion region and behaves like a thinner detector thus exhibiting better collection efficiencies. Therefore, medium resistivity
material which is completely inadequate for resistive detectors can still yield high performance Schottky detectors. The preferred
direction of irradiation, i.e. from the negative electrode, is possible only in the case of n-type material which is reverse
biased by negative voltages applied to the Schottky gate. The mobility-lifetime products that are derived on both the resistive
detector (with specific resistivity of ≈1.1010 ω.cm) and the Schottky diode (with specific resistivity of ≈1.106 Ω.cm) are μnτn ≈-4.10−4 cm2V−1 and μpτp≅ 8.10−5 cm2V−1. 相似文献
2.
Study of contacts to CdZnTe radiation detectors 总被引:1,自引:0,他引:1
This study characterizes, for the first time, contacts to CdZnTe radiation detectors by measuring the dark noise spectra as
a function of the applied bias. The noise currents are correlated with the dc dark current-voltage characteristics of CdZnTe
x-ray and gamma-ray detectors. In order to identify and separate the role of the contacts in the overall performance, the
measured noise phenomena is correlated with detector configuration and contact design as well as the growth method of the
CdZnTe crystals, contact technology, and passivation. Several contact technologies (electroless gold, and a number of evaporated
metallic contacts including gold, indium, zinc, titanium, aluminum, and platinum contacts) are compared. Contacts to CdZnTe
crystals grown by high pressure Bridgman are compared with contacts to CdZnTe crystals grown by modified Bridgman. Contacts
of resistive detectors as well as of Schottky detectors are reported. Large area symmetric contacts are compared with small
area pixelized contacts. The role of the metallization used for contacts, the role of surface effects and passivation, and
the role of contact design are discussed. 相似文献
3.
H. B. Barber H. H. Barrett F. L. Augustine W. J. Hamilton B. A. Apotovsky E. L. Dereniak F. P. Doty J. D. Eskin J. P. Garcia D. G. Marks K. J. Matherson J. M. Woolfenden E. T. Young 《Journal of Electronic Materials》1997,26(6):765-772
Previous work has shown that hybrid semiconductor detector arrays similar to those used in infrared focal-plane arrays are
very attractive for use in nuclear medicine and other gamma-ray imaging applications. In this paper, we describe the development
of a 64 × 64 readout multiplexer specifically for use in gamma-ray imaging; we also describe the construction of 64 × 64 CdZnTe
hybrid detector arrays using the new readout. The readout and detector array are both about one inch square (2.5 cm × 2.5
cm) and have 380 μm pixel pitch. Some initial assembly problems have been resolved by stabilizing the hybrids with epoxy.
Preliminary testing results are presented that verify that the 64 × 64 CdZnTe arrays perform as excellent imaging spectrometers. 相似文献
4.
J. M. Van Scyoc J. C. Lund D. H. Morse A. J. Antolak R. W. Olsen R. B. James M. Schieber H. Yoon M. S. Goorsky J. Toney T. E. Schlesinger 《Journal of Electronic Materials》1996,25(8):1323-1327
Cadmium zinc telluride (Cd1−x ZnxTe or CZT) has shown great promise as a material for room temperature x-ray and gamma-ray detectors. In particular, polycrystalline
material grown by the high pressure Bridgman method with nominal Zn fraction (x) from 0.1 to 0.2 has been used to fabricate
high resolution gamma-ray spectrometers with resolution approaching that of cooled high-purity Ge. For increased sensitivity,
large areas (> 1 cm2) are required, and for good sensitivity to high energy gamma photons, thick detectors (on the order of 1 cm) are required.
Thus, there has been a push for the development of CZT detectors with a volume greater than 1 cm3. However, nonuniformities in the material over this scale degrade the performance of the detectors. Variations in the zinc
fraction, and thus the bandgap, and changes in the impurity distributions, both of which arise from the selective segregation
of elements during crystal growth, result in spectral distortions. In this work, several materials characterization techniques
were combined with detector evaluations to determine the materials properties limiting detector performance. Materials measurements
were performed on detectors found to have differing performance. Measurements conducted include infrared transmission, particle
induced x-ray emission, photoluminescence, and triaxial x-ray diffraction. To varying degrees, these measurements reveal that
“poor-performance” detectors exhibit higher nonuniformities than “spectrometer-grade” detectors. This is reasonable, as regions
of CZT material with different properties will give different localized spectral responses, which combine to result in a degraded
spectrum for the total device. 相似文献
5.
Readout electronics,especially digital electronics,for two-element CdZnTe(CZT) detectors in parallel are developed.The preliminary results show the detection efficiency of the two-element CZT detectors in parallel with analog electronics is as many as 1.8 and 2.1 times the single ones,and the energy resolution(FWHM) is limited by that of the single one by the means of analog electronics.However,the digital method for signal processing will be sufficiently better by contrast with an analog method especial... 相似文献
6.
7.
The transport, trapping, and subsequent detrapping of charge in single crystals of semi-insulating cadmium zinc telluride
(CdZnTe) has been analyzed using multiple-scale perturbation techniques. This method has the advantage of not only treating
impulse charge generation typical in spectroscopic analysis, but also a large class of continuous generation sources more
relevant to high-flux x-ray imaging applications. We first demonstrate that the multiple-scale solutions obtained for small-current
transients induced by an impulse generation of charge are consistent with well-known exact solutions. Further, we use the
multiple-scale solutions to derive an analytic generalization of the Hecht equation that incorporates detrapping over times
much longer than the carrier transit time (i.e., delayed signal components). The method is then applied to a continuous charge
generation source that approximates that of an x-ray source. The space–time solutions obtained are relevant to detector design
in high-flux x-ray imaging applications. Throughout this work the multiple-scale solutions are compared with exact solutions
as well as full numerical solutions of the fundamental charge conservation equations. 相似文献
8.
Martine C. Duff Douglas B. Hunter Patterson Nuessle David R. Black Harold Burdette Joseph Woicik Arnold Burger Michael Groza 《Journal of Electronic Materials》2007,36(8):1092-1097
Synthetic CdZnTe (CZT) crystals can be used for the room temperature-based detection of gamma radiation. Structural/morphological
heterogeneities within CZT, such as secondary phases (namely, precipitates and inclusions), can negatively affect detector
performance. We used a synchrotron-based x-ray technique, specifically extended x-ray absorption fine-structure (EXAFS) spectroscopy,
to determine whether there are differences on a local structural level between intact CZT of high and low radiation detector
performance. These studies were complemented by data on radiation detector performance and transmission infrared (IR) imaging.
The EXAFS studies revealed no detectable local structural differences between the two types of CZT materials. 相似文献
9.
S. Terterian M. Chu D. Ting L. C. Wu C. C. Wang M. Szawlowski G. Vissor P. N. Luke 《Journal of Electronic Materials》2003,32(7):796-802
A large number of room-temperature detectors have been produced from CdZnTe crystals grown with 10% Zn and 1.5% excess tellurium
by the low-pressure, vertical-Bridgman technique. Radiation spectra obtained by these crystals using a 241Am source reveal the characteristic 59.5-keV line as well as the six low-energy peaks, which include the Cd and Te escape
peaks. Similarly, 57Co spectra obtained also show a very well-defined 122-keV peak with a 3:1 peak-to-valley ratio. Seven CdZnTe crystals have
been grown for reproducibility studies. Four of these crystals have resistivities over 1E9 Ω-cm. Considering that the indiumdoping
level is on the order of 2E15 cm−3, the reproducibility is excellent. The theoretical basis of the high-resistivity phenomenon in CdZnTe is discussed in reference
to a previous paper. The uniformity of these 6-in.-long CdZnTe crystals is studied, and various measurements are carried out,
both laterally and vertically, along the boule. It is determined that, in general, roughly a 3.5-in. section near the middle
of the 6-in. boule has sufficient resistivity for producing radiation detectors. This nonuniformity along the vertical direction
is caused mostly by the composition change of Cd, Zn, Te, and In-doping level in the growth melt caused by differences in
the segregation coefficients of these elements. Although, variations in resistivity are seen across some of the wafer slices,
most show very good uniformity with high breakdown voltage. Some of the variations are attributed to the different grains
within the boule. Similar results are seen in the measured radiation spectra obtain on 4 mm × 4 mm × 2 mm samples from different
locations across the wafer, where some samples show well-resolved secondary peaks, while others display only the primary spectral
lines. 相似文献
10.
J. C. Erickson H. W. Yao R. B. James H. Hermon M. Greaves 《Journal of Electronic Materials》2000,29(6):699-703
A time of flight technique was used to study the carrier trapping time, τ, and mobility, μ, in CdZnTe (CZT) and CdTe radiation
detectors. Carriers were generated near the surface of the detector by a nitrogen-pumped pulsed dye laser with wavelength
∼500 nm. Signals from generated electrons or holes were measured by a fast oscilloscope and analyzed to determine the trapping
time and mobility of carriers. Electron mobility was observed to change with temperature from 1200 cm2/Vs to 2400 cm2/Vs between 293 K and 138 K, respectively. Electron mobilities were observed between 900 cm2/Vs and 1350 cm2/Vs at room temperature for various CZT detectors. Electron mobilities in various CdTe detectors at room temperature were
observed between 740 cm2/Vs and 1260 cm2/Vs. Average electron mobility was calculated to be 1120 cm2/Vs and 945 cm2/Vs for CZT and CdTe, respectively. Hole mobilities in both CZT and CdTe were found to vary between 27 cm2/Vs and 66 cm2/Vs. Electron trapping times in CZT at room temperature varied from 1.60 μs to 4.18 μs with an average value of about 2.5
μs. Electron trapping time in CdTe at room temperature varied between 1.7 μs and 4.15 μs with an average value of about 3.1
μs. 相似文献
11.
This work focuses on the evaluation of the spectroscopic performance of n-type CdZnTe gamma-ray spectrometers, grown by a
modified horizontal Bridgman Technique developed at IMARAD Imaging Systems Ltd. Two types of devices are studied: (i) detector
arrays grown and produced by IMARAD and employing ohmic indium contacts and (ii) detectors and arrays fabricated at Technion
in crystals provided by IMARAD, employing different types of contacts. Alpha particle spectroscopy as well as gamma-ray spectroscopy
is used to evaluate and characterize the energy resolution of gamma-ray spectrometers fabricated on n-type CdZnTe grown by
a modified horizontal Bridgman and doped with indium. The electron and hole mobility lifetime products of the n-type CdZnTe
material grown by IMARAD are estimated by measuring the dependence of charge collection efficiency upon the bias voltage,
using a calibrated multichannel analyzer. The measured results indicate that the average electron and hole mobility-lifetime
products are, respectively, of the order of μnτn=(1–2)·10−3 cm2/V and μpτp=6·10−6 cm2/V. The measured energy resolution of 122 keV photons is −(5–6)% when the source is not collimated and is reduced to −4.5%
when the source is collimated. These results are obtained with ohmic cathode as well as with a rectifying cathode. A statistical
model for the calculation of the pulse height spectra as a function of photon energy, electron and hole mobility-lifetime
products and applied electric field, which has been recently reported in Applied Physical Letters, is used to determine the role of incomplete charge collection in the spectral performance of the n-type CdZnTe spectrometers.
The comparison between the measured and modeled results indicates that the dark noise, cross talk and non-uniformity are the
main limiting factors of the spectral performance of the n-type spectrometers rather than incomplete charge collection. The
good spectroscopic performance of the arrays under study is attributed to an adequate hole mobility lifetime for the geometry
of the pixilated arrays. The study indicates that the n-type CdZnTe spectrometers are useful for a wide range of imaging applications. 相似文献
12.
W. J. Hamilton D. R. Rhiger S. Sen M. H. Kalisher G. R. Chapman R. E. Mills 《Journal of Electronic Materials》1996,25(8):1286-1292
Classical solid-state detection of x-ray and gamma-ray radiation consists of a high voltage applied between two metallic contacts
sandwiching a high resistivity, high dielectric strength material; high voltage and high resistivity are required to enable
complete charge collection while minimizing the resolution-degrading leakage current (dark current). We report here the conception
and successful fabrication and test of a new device construct which changes this paradigm. P-type and n-type layers are fabricated
by mercury cadmium telluride (HC.T) liquid phase epitaxy (LPE) on opposite sides of a high-quality wafer of CdZnTe (CZT) in
order to construct a p-i-n diode structure. Wafers up to 9 cm2 area have been grown. This diode structure provides an extremely high effective resistivity and barrier to the flow of dark
current in the device. Several wafer lots have repeatably yielded p-i-n detectors which exhibit typical diode current-voltage
(I-V) curves with very low dark currents at very high bias voltages. Spectra obtained from these detectors produce exceptionally
sharp photopeaks which exhibit very little low-energy tailing. 相似文献
13.
碲锌镉(CdZnTe)半导体材料具有探测效率高、能量分辨率高和体积小重量轻的特点,是公认的最有希望成为下一代伽马射线探测装置的材料。然而,空穴俘获导致的电荷收集不完全限制了碲锌镉半导体探测器的性能。解决空穴俘获最有效的方法是单极型探测器技术。文章首先简要介绍半导体探测器中电荷收集的相关理论,然后重点阐述单极型探测器技术的实现方法,包括各种电极的结构设计原理、典型的探测器原型机介绍、性能特点及其结构设计的优缺点。最后简要展望了碲锌镉半导体探测器未来的发展方向。 相似文献
14.
H. Bradford Barber 《Journal of Electronic Materials》1996,25(8):1232-1240
Semiconductor gamma-ray detector arrays made of II-VI materials such as CdTe or CdZnTe hold great promise for improving the
spatial resolution and energy resolution of nuclear medicine imaging systems. This field has benefited greatly from technologies
developed in infrared imaging. This report surveys the state of the art for producing high-resolution semiconductor arrays
with emphasis on II-VI materials and considers the prospects for producing a semiconductor detector gamma camera. A number
of practical designs are reviewed that make use of single-charge-carrier dominance effects to improve useful photopeak fraction
and thus efficiency. 相似文献
15.
Fabrication and characterization of CdZnTe radiation detectors with a new P-I-N design 总被引:2,自引:0,他引:2
We report on the design, fabrication, and performance of CdZnTe gamma-ray detectors with a new P-I-N structure for spectroscopic
applications. Highpressure and conventional vertical-Bridgman CdZnTe crystals were used for detector fabrication. P and n
layers were deposited by thermal evaporation, and by optimizing the deposition conditions we achieved low leakage current
(approximately 15 nA at 1000 V) and good performance. Spectral response data at high bias voltages showed improved energy
resolution and peak-to-valley ratios for 241Am and 57Co compared to metal-semiconductor-metal detectors. 相似文献
16.
17.
A CdZnTe detector grown by the high pressure Bridgman (HPB) growth technique was tested using high energy x-rays (30∼100 keV),
and the performance was compared with a commercially available Nal scintillating detector of 5 cm thickness. The charge collection
efficiency of a CdZnTe detector is as high as 90% at relatively low electric field, 600 V/cm. At high x-ray photon energies,
the detection efficiency is reduced due to the thickness of the CdZnTe. A 32 channel linear array was fabricated on 1.2∼1.7
mm thick CdZnTe, of which the detector area was 175 × 800 μm2 and the pitch size 250 μm. The measured dark current for the 16 element detector was as low as 0.1 pA at 800 V/cm with an
excellent uniformity. Energy spectra were measured using a Co57 radiation source. A small pixel effect and charge sharing were observed. The energy resolution was improved and compared
with the large area detector. The array detector gave an average 5.8% full-width-half-maximum (FWHM) at 122 keV photopeak.
The large area detector of the same material before fabrication exhibited a low energy tail at the photopeak, which limits
the photopeak FWHM to 8%. 相似文献
18.
Muren Chu Sevag Terterian David Ting C. C. Wang J. D. Benson J. H. Dinan R. B. James Arnold Burger 《Journal of Electronic Materials》2003,32(7):778-782
Room-temperature radiation detectors have been fabricated on high-resistivity, indium-doped Cd0.90Zn0.10Te crystals grown under different amounts of excess Te. The effects of the excess Te on the properties of the detectors are
explained by a simple model using only three parameters: the density of Cd vacancies, the density of Te antisites (Te at Cd
sites), and the deep level of doubly ionized Te antisites. The best detectors, which can resolve the low-energy Np-L and Te-K
peaks as well as Cd and Te escape peaks of 241Am, are produced from crystals grown with 1.5% excess Te. The detectors fabricated from crystals grown without excess Te are
unable to resolve any characteristic-radiation peaks of 241Am and 57Co. This result is explained by a model of networked p-type domains in an n-type matrix or vice versa, which is caused by
the lack of sufficient deep-level Te antisites. Such conduction-type inhomogeneity causes massive electron and hole trapping.
As for the detectors fabricated from Cd0.90Zn0.10Te crystals grown with 2% and 3% excess Te, they are able to resolve the 241Am 59.5-keV, 57Co 122-keV, and 57Co 136-keV radiation peaks. However, the full-width at half-maximum (FWHM) values of these peaks are broadened, especially
the high-energy 57Co peaks. These phenomena are attributed to the hole and, possibly, electron trapping by Cd vacancies and Te antisites, respectively.
The result of the analysis indicates that sufficient Te antisites and a low density of carrier traps in Cd0.90Zn0.10Te are essential for producing high-quality radiation detectors. In the analysis, it was discovered that most of the excess
Te, on the order of 1–2 × 1020 cm−3, remain electrically inactive. A possible explanation for this phenomenon is that the excess Te atoms form neutral Te-antisite
and Cd-vacancy complexes, such as TeCd·(VCd)2, during the post-growth cooling process. 相似文献
19.
红外光热吸收效应作为一种无损伤非接触的检测技术,已经被广泛用于硅等半导体材料中的微缺陷表征分析.采用光热吸收技术对碲锌镉晶体中的缺陷进行扫描成像分析时发现了一种连续性的光貌相条纹,并对这些条纹的形成机理进行了研究.研究表明碲锌镉晶体中的这种连续性条纹源自于光热测试系统中入射光的干涉,这种干涉和入射光参数、测试样品的厚度、禁带宽度以及热导率等材料特性密切相关.最后,实验通过优化红外光热吸收测量系统获得了碲锌镉材料中的微缺陷结构及其在样品深度方向的三维分布图像. 相似文献
20.
Y. Nemirovsky G. Asa C. G. Jakobson A. Ruzin J. Gorelik 《Journal of Electronic Materials》1998,27(6):800-806
The effect on energy resolution of dark noise currents experimentally observed in state of the art CdZnTe spectrometers is
quantitatively analyzed. Expressions for the energy resolution determined by shot noise, generation-recombination noise, and
1/f noise are discussed in turn and are compared with the linewidth due to incomplete charge collection. The effect of the
dark noise upon energy resolution is directly measured by monitoring the broadening of peaks provided by a pulser, due to
biased, non-irradiated CdZnTe spectrometers that are connected in parallel. The noise characteristics of the spectrometers
under study were measured separately and their dominant noise mechanism is characterized. In this manner, the effect on resolution
of the dark noise is correlated not only with the dc value of the dark current but also with the noise spectral behavior which
is determined by the noise mechanism. 相似文献