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Sample records for cdte cdznte detectors

  1. Progress in the Development of CdTe and CdZnTe Semiconductor Radiation Detectors for Astrophysical and Medical Applications

    PubMed Central

    Sordo, Stefano Del; Abbene, Leonardo; Caroli, Ezio; Mancini, Anna Maria; Zappettini, Andrea; Ubertini, Pietro

    2009-01-01

    Over the last decade, cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) wide band gap semiconductors have attracted increasing interest as X-ray and gamma ray detectors. Among the traditional high performance spectrometers based on silicon (Si) and germanium (Ge), CdTe and CdZnTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact and reliable detection systems. In this paper, we review the current status of research in the development of CdTe and CdZnTe detectors by a comprehensive survey on the material properties, the device characteristics, the different techniques for improving the overall detector performance and some major applications. Astrophysical and medical applications are discussed, pointing out the ongoing Italian research activities on the development of these detectors. PMID:22412323

  2. Energy dispersive CdTe and CdZnTe detectors for spectral clinical CT and NDT applications

    NASA Astrophysics Data System (ADS)

    Barber, W. C.; Wessel, J. C.; Nygard, E.; Iwanczyk, J. S.

    2015-06-01

    We are developing room temperature compound semiconductor detectors for applications in energy-resolved high-flux single x-ray photon-counting spectral computed tomography (CT), including functional imaging with nanoparticle contrast agents for medical applications and non-destructive testing (NDT) for security applications. Energy-resolved photon-counting can provide reduced patient dose through optimal energy weighting for a particular imaging task in CT, functional contrast enhancement through spectroscopic imaging of metal nanoparticles in CT, and compositional analysis through multiple basis function material decomposition in CT and NDT. These applications produce high input count rates from an x-ray generator delivered to the detector. Therefore, in order to achieve energy-resolved single photon counting in these applications, a high output count rate (OCR) for an energy-dispersive detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) compound semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel provided the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions, and at a sufficiently high detective quantum efficiency (DQE). We have developed high-flux energy-resolved photon-counting x-ray imaging array sensors using pixellated CdTe and CdZnTe semiconductors optimized for clinical CT and security NDT. We have also fabricated high

  3. Energy dispersive CdTe and CdZnTe detectors for spectral clinical CT and NDT applications

    PubMed Central

    Barber, W. C.; Wessel, J. C.; Nygard, E.; Iwanczyk, J. S.

    2014-01-01

    We are developing room temperature compound semiconductor detectors for applications in energy-resolved high-flux single x-ray photon-counting spectral computed tomography (CT), including functional imaging with nanoparticle contrast agents for medical applications and non destructive testing (NDT) for security applications. Energy-resolved photon-counting can provide reduced patient dose through optimal energy weighting for a particular imaging task in CT, functional contrast enhancement through spectroscopic imaging of metal nanoparticles in CT, and compositional analysis through multiple basis function material decomposition in CT and NDT. These applications produce high input count rates from an x-ray generator delivered to the detector. Therefore, in order to achieve energy-resolved single photon counting in these applications, a high output count rate (OCR) for an energy-dispersive detector must be achieved at the required spatial resolution and across the required dynamic range for the application. The required performance in terms of the OCR, spatial resolution, and dynamic range must be obtained with sufficient field of view (FOV) for the application thus requiring the tiling of pixel arrays and scanning techniques. Room temperature cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) compound semiconductors, operating as direct conversion x-ray sensors, can provide the required speed when connected to application specific integrated circuits (ASICs) operating at fast peaking times with multiple fixed thresholds per pixel provided the sensors are designed for rapid signal formation across the x-ray energy ranges of the application at the required energy and spatial resolutions, and at a sufficiently high detective quantum efficiency (DQE). We have developed high-flux energy-resolved photon-counting x-ray imaging array sensors using pixellated CdTe and CdZnTe semiconductors optimized for clinical CT and security NDT. We have also fabricated high

  4. PERFORMANCE-LIMITING DEFECTS IN CDZNTE DETECTORS.

    SciTech Connect

    BOLOTNIKOV, A.E.; CAMARDA, G.S.; CUI, Y.; KOHMAN, K.T.; LI, L.; SALOMON, M.B.; JAMES, R.B.

    2006-10-29

    We studied the effects of small, <20 {micro}m, Te inclusions on the energy resolution of CdZnTe gamma-ray detectors using a highly collimated X-ray beam and gamma-rays, and modeled them via a simplified geometrical approach. Previous reports demonstrated that Te inclusions of about a few microns in diameter degraded the charge-transport properties and uniformity of CdZnTe detectors. The goal of this work was to understand the extent to which randomly distributed Te-rich inclusions affect the energy resolution of CZT detectors, and to define new steps to overcome their deleterious effects. We used a phenomenological model, which depends on several adjustable parameters, to reproduce the experimentally measured effects of inclusions on energy resolution. We also were able to hound the materials-related problem and predict the enhancement in performance expected by reducing the size and number of Te inclusions within the crystals.

  5. Optimal width of barrier region in X/{gamma}-ray Schottky diode detectors based on CdTe and CdZnTe

    SciTech Connect

    Kosyachenko, L. A.; Melnychuk, S. V.; Sklyarchuk, V. M.; Maslyanchuk, O. L.; Sklyarchuk, O. V.; Aoki, T.; Lambropoulos, C. P.; Gnatyuk, V. A.; Grushko, E. V.

    2013-02-07

    The spectral distribution of quantum detection efficiency of X- and {gamma}-ray Schottky diodes based on semi-insulating CdTe or Cd{sub 0.9}Zn{sub 0.1}Te crystals is substantiated and obtained in analytical form. It is shown that the width of the space charge region (SCR) of 6-40 {mu}m at zero bias in CdTe (Cd{sub 0.9}Zn{sub 0.1}Te) Schottky diode is optimal for detecting radiation in the photon energy range above 5-10 keV. Based on the Poisson equation, the relationship between the SCR width and the composition of impurities and the degree of their compensation are investigated. It is shown that the presence of deep levels in the bandgap leads to a considerable increase in space charge density and electric field strength near the crystal surface. However, this effect contributes a small error in the determination of the SCR width using the standard formula for the Schottky diode. It is also shown that the concentration of uncompensated impurities in CdTe and Cd{sub 0.9}Zn{sub 0.1}Te crystals within the 4 Multiplication-Sign 10{sup 11}-10{sup 13} cm{sup -3} range is optimal for the detection efficiency of X- and {gamma}-rays in the photon high-energy range. The record-high values of energy resolution have been obtained in the spectra of {sup 241}Am, {sup 57}Co, {sup 133}Ba and {sup 137}Cs isotopes measured using CdTe crystals with Schottky diodes because the concentration of uncompensated donors in the CdTe crystals (1-2) Multiplication-Sign 10{sup 12} cm{sup -3} falls on an interval of maximum detection efficiency. In the spectrum of {sup 57}Co isotope, the limiting energy resolution has been achieved.

  6. Optimal width of barrier region in X/γ-ray Schottky diode detectors based on CdTe and CdZnTe

    NASA Astrophysics Data System (ADS)

    Kosyachenko, L. A.; Aoki, T.; Lambropoulos, C. P.; Gnatyuk, V. A.; Melnychuk, S. V.; Sklyarchuk, V. M.; Grushko, E. V.; Maslyanchuk, O. L.; Sklyarchuk, O. V.

    2013-02-01

    The spectral distribution of quantum detection efficiency of X- and γ-ray Schottky diodes based on semi-insulating CdTe or Cd0.9Zn0.1Te crystals is substantiated and obtained in analytical form. It is shown that the width of the space charge region (SCR) of 6-40 μm at zero bias in CdTe (Cd0.9Zn0.1Te) Schottky diode is optimal for detecting radiation in the photon energy range above 5-10 keV. Based on the Poisson equation, the relationship between the SCR width and the composition of impurities and the degree of their compensation are investigated. It is shown that the presence of deep levels in the bandgap leads to a considerable increase in space charge density and electric field strength near the crystal surface. However, this effect contributes a small error in the determination of the SCR width using the standard formula for the Schottky diode. It is also shown that the concentration of uncompensated impurities in CdTe and Cd0.9Zn0.1Te crystals within the 4 × 1011-1013 cm-3 range is optimal for the detection efficiency of X- and γ-rays in the photon high-energy range. The record-high values of energy resolution have been obtained in the spectra of 241Am, 57Co, 133Ba and 137Cs isotopes measured using CdTe crystals with Schottky diodes because the concentration of uncompensated donors in the CdTe crystals (1-2) × 1012 cm-3 falls on an interval of maximum detection efficiency. In the spectrum of 57Co isotope, the limiting energy resolution has been achieved.

  7. CdZnTe technology for gamma ray detectors

    SciTech Connect

    Stahle, Carl; Shi, Jack; Shu, Peter; Barthelmy, Scott; Parsons, Ann; Snodgrass, Steve

    1998-01-15

    CdZnTe detector technology has been developed at NASA Goddard for imaging and spectroscopy applications in hard x-ray and gamma ray astronomy. A CdZnTe strip detector array with capabilities for arc second imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. CdZnTe detectors also have applications for medical imaging, environmental protection, transportation safety, nuclear safeguards and safety, nuclear non-proliferation, and national security. This can be accomplished from space and also from portable detectors on earth. One of the great advantages of CdZnTe is that the detectors can be operated at room temperature which eliminates the need for cryogenic cooling. CdZnTe detectors have good energy resolution (3.6 keV at 60 keV) and excellent spatial resolution (<100 microns). NASA Goddard has developed the fabrication technology to make a variery of planar, strip, and pixel detectors and integrated these detectors to high density electronics. We have built a 2x2 and a large area (60 cm{sup 2}, 36 detectors) 6x6 strip detector array. This paper will summarize the CdZnTe detector fabrication and packaging technology developed at Goddard.

  8. Development of prototype pixellated PIN CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Narita, Tomohiko; Bloser, Peter F.; Grindlay, Jonathan E.; Sudharsanan, R.; Reiche, C.; Stenstrom, Claudia

    1998-07-01

    We report initial results from the design and evaluation of two pixellated PIN Cadmium Zinc Telluride detectors and an ASIC-based readout system. The prototype imaging PIN detectors consist of 4 X 4 1.5 mm square indium anode contacts with 0.2 mm spacing and a solid cathode plane on 10 X 10 mm CdZnTe substrates of thickness 2 mm and 5 mm. The detector readout system, based on low noise preamplifier ASICs, allows for parallel readout of all channels upon cathode trigger. This prototype is under development for use in future astrophysical hard X-ray imagers with 10 - 600 keV energy response. Measurements of the detector uniformity, spatial resolution, and spectral resolution will be discussed and compared with a similar pixellated MSM detector. Finally, a prototype design for a large imaging array is outlined.

  9. READOUT SYSTEM FOR ARRAYS OF FRISCH-RING CDZNTE DETECTORS.

    SciTech Connect

    CUI, Y.; BOLOTNIKOV, A.E.; CAMARDA, G.S.; DE GERONIMO, G.; O'CONNOR, P.; JAMES, R.B.; KARGAR, A.; HARRISON, M.J.; MCGREGOR, D.S.

    2006-10-29

    Frisch-ring CdZnTe detectors have demonstrated good energy resolution for identifying isotopes, <1% FWHM at 662 keV, and good efficiency for detecting gamma rays. We will fabricate and test at Brookhaven National Laboratory an integrated module of a 64-element array of 6 x 6 x 12 mm{sup 3} Frisch-ring detectors, coupled with a readout electronics system. It supports 64 readout channels, and includes front-end electronics, signal processing circuit, USB interface and high-voltage power supply. The data-acquisition software is used to process the data stream, which includes amplitude and timing information for each detected event. This paper describes the design and assembly of the detector modules, readout electronics, and a conceptual prototype system. Some test results are also reported.

  10. CHARACTERIZATION OF DETECTOR GRADE CDZNTE MATERIAL FROM REDLEN TECHNOLOGIES

    SciTech Connect

    Duff, M

    2008-07-09

    CdZnTe (or CZT) crystals can be used in a variety of detector-type applications. This large band gap material shows great promise for use as a gamma radiation spectrometer. Historically, the performance of CZT has typically been adversely affected by point defects, structural and compositional heterogeneities within the crystals, such as twinning, pipes, grain boundaries (polycrystallinity) and secondary phases (SP). The synthesis of CZT material has improved greatly with the primary performance limitation being attributed to mainly SP. In this presentation, we describe the extensive characterization of detector grade material that has been treated with post growth annealing to remove the SPs. Some of the analytical methods used in this study included polarized, cross polarized and transmission IR imaging, I-V curves measurements, synchrotron X-ray topography and electron microscopy.

  11. Nuclear reactor pulse calibration using a CdZnTe electro-optic radiation detector.

    PubMed

    Nelson, Kyle A; Geuther, Jeffrey A; Neihart, James L; Riedel, Todd A; Rojeski, Ronald A; Saddler, Jeffrey L; Schmidt, Aaron J; McGregor, Douglas S

    2012-07-01

    A CdZnTe electro-optic radiation detector was used to calibrate nuclear reactor pulses. The standard configuration of the Pockels cell has collimated light passing through an optically transparent CdZnTe crystal located between crossed polarizers. The transmitted light was focused onto an IR sensitive photodiode. Calibrations of reactor pulses were performed using the CdZnTe Pockels cell by measuring the change in the photodiode current, repeated 10 times for each set of reactor pulses, set between 1.00 and 2.50 dollars in 0.50 increments of reactivity.

  12. Performance of CdZnTe detectors passivated with energetic oxygen atoms

    SciTech Connect

    Prettyman, T.H.; Hoffbauer, M.A.; Rennie, J.

    1998-12-01

    Noise caused by surface-leakage current can degrade the performance of CdZnTe spectrometers, particularly devices with closely spaced contacts such as coplanar grid detectors. In order to reduce surface leakage, the authors are treating CdZnTe detector surfaces with energetic, neutral oxygen atoms. Energetic oxygen atoms react with the surface to form a resistive oxide layer. Because the reaction is effective at room temperature, deleterious heating of the substrate is avoided. In most cases, leakage current and noise are shown to decrease significantly after treatment. The effect of the treatment on the performance of coplanar grid detectors is presented.

  13. The X-ray response of CdZnTe detectors to be used as future spectroscopic detectors for X-ray astronomy

    NASA Astrophysics Data System (ADS)

    Kraft, S.; Bavdaz, M.; Castelletto, B.; Peacock, A.; Scholze, F.; Ulm, G.; Gagliardi, M.-A.; Nenonen, S.; Tuomi, T.; Juvonen, M.; Rantamäki, R.

    1998-12-01

    The next generation of X-ray astrophysics missions may well extend the energy range beyond the current limit of about 10keV studied by the existing X-ray Astrophysics space missions such as ASCA or future missions such as AXAF and XMM to be launched in the next few years. To address with a high degree of sensitivity the astrophysical problems associated with X-ray emission in the X-ray band from 0.2 to 100keV a significant extension of the capabilities of focusing X-ray optics and imaging broad band hard X-ray detectors will be required. Future missions such as INTEGRAL, BASIS and EXIST will make use of CdZnTe or CdTe detectors for imaging spectroscopy down to about 5keV with a spectral resolution between 3% and 7% at 100keV. This is about a factor of 10 away from what is theoretically possible and mainly caused by the poor crystal quality. In this paper experimental results on the study of the X-ray response of CdZnTe detectors are presented. The detector response to photons with energies between 1 and 5keV has been investigated using synchrotron radiation and a preliminary model to describe the detector response developed. The limitations on the energy resolution, due to incomplete charge collection and spatial non-uniformities, are presented based on the detailed mapping of the energy response of a detector exposed to highly monochromatised synchrotron radiation. At higher energies results have been obtained using a 241Am radioactive source and an electron cyclotron resonance source so as to establish the detector performance and overall response to medium- and higher-energy X-ray photons up to 60keV. Based on these results the performance of the detectors are compared with Si(Li) and HPGe solid-state detectors.

  14. Fabrication of CdZnTe strip detectors for large area arrays

    SciTech Connect

    Stahle, C.M.; Shi, Z.Q.; Hu, K.

    1998-12-31

    A CdZnTe strip detector large area array ({approximately} 60 cm{sup 2} with 36 detectors) with capabilities for high resolution imaging and spectroscopy has been built as a prototype for a space flight gamma ray burst instrument. The detector array also has applications in nuclear medical imaging. Two dimensional orthogonal strip detectors with 100 {micro}m pitch have been fabricated and tested. Details for the array design, fabrication and evaluation of the detectors will be presented.

  15. Ruggedization of CdZnTe detectors and detector assemblies for radiation detection applications

    NASA Astrophysics Data System (ADS)

    Lu, P. H.; Gomolchuk, P.; Chen, H.; Beitz, D.; Grosser, A. W.

    2015-06-01

    This paper described improvements in the ruggedization of CdZnTe detectors and detector assemblies for use in radiation detection applications. Research included experimenting with various conductive and underfill adhesive material systems suitable for CZT substrates. A detector design with encapsulation patterning was developed to protect detector surfaces and to control spacing between CZT anode and PCB carrier. Robustness of bare detectors was evaluated through temperature cycling and metallization shear testing. Attachment processes using well-chosen adhesives and PCB carrier materials were optimized to improve reliability of detector assemblies, resulted in Improved Attachment Detector Assembly. These detector assemblies were subjected to aggressive temperature cycling, and varying levels of drop/shock and vibration, in accordance with modified JEDEC, ANSI and FedEx testing standards, to assess their ruggedness. Further enhanced detector assembly ruggedization methods were investigated involving adhesive conformal coating, potting and dam filling on detector assemblies, which resulted in the Enhanced Ruggedization Detector Assembly. Large numbers of CZT detectors and detector assemblies with 5 mm and 15 mm thick, over 200 in total, were tested. Their performance was evaluated by exposure to various radioactive sources using comprehensive predefined detector specifications and testing protocols. Detector assemblies from improved attachment and enhanced ruggedization showed stable performances during the harsh environmental condition tests. In conclusion, significant progress has been made in improving the reliability and enhancing the ruggedness of CZT detector assemblies for radiation detection applications deployed in operational environments.

  16. Preliminary results obtained from novel CdZnTe pad detectors

    SciTech Connect

    Tuemer, T.O.; Joyce, D.C.; Yin, S.; Willson, P.D.; Parnham, K.B.; Glick, B.

    1996-06-01

    CdZnTe pad detectors with a novel geometry and approximately 1 mm{sup 2} pad sizes are being developed. These detectors have been specially designed for high energy resolution up to 300 keV energies. The contacts are produced through a unique technique developed by eV Products to achieve high reliability low resistance coupling to the substrate. A ceramic carrier is developed for low capacitance coupling of the detectors to NOVA`s FEENA chip. The detectors have been tested using the ultra low noise single and 3-channel amplifiers developed by eV Products. The CdZnTe detectors are tested for dark current. The charge energy resolutions and collection times are also measured using natural radiation sources. The measured detector parameters and the test results are showing that linear pad arrays can have good uniformity and excellent application potential for imaging x-rays and gamma-rays.

  17. Hard x-ray response of pixellated CdZnTe detectors

    SciTech Connect

    Abbene, L.; Caccia, S.; Bertuccio, G.

    2009-06-15

    In recent years, the development of cadmium zinc telluride (CdZnTe) detectors for x-ray and gamma ray spectrometry has grown rapidly. The good room temperature performance and the high spatial resolution of pixellated CdZnTe detectors make them very attractive in space-borne x-ray astronomy, mainly as focal plane detectors for the new generation of hard x-ray focusing telescopes. In this work, we investigated on the spectroscopic performance of two pixellated CdZnTe detectors coupled with a custom low noise and low power readout application specific integrated circuit (ASIC). The detectors (10x10x1 and 10x10x2 mm{sup 3} single crystals) have an anode layout based on an array of 256 pixels with a geometric pitch of 0.5 mm. The ASIC, fabricated in 0.8 mum BiCMOS technology, is equipped with eight independent channels (preamplifier and shaper) and characterized by low power consumption (0.5 mW/channel) and low noise (150-500 electrons rms). The spectroscopic results point out the good energy resolution of both detectors at room temperature [5.8% full width at half maximum (FWHM) at 59.5 keV for the 1 mm thick detector; 5.5% FWHM at 59.5 keV for the 2 mm thick detector) and low tailing in the measured spectra, confirming the single charge carrier sensing properties of the CdZnTe detectors equipped with a pixellated anode layout. Temperature measurements show optimum performance of the system (detector and electronics) at T=10 deg.C and performance degradation at lower temperatures. The detectors and the ASIC were developed by our collaboration as two small focal plane detector prototypes for hard x-ray multilayer telescopes operating in the 20-70 keV energy range.

  18. CdZnTe detectors for gamma-ray Burst ArcSecond Imaging and Spectroscopy (BASIS)

    NASA Astrophysics Data System (ADS)

    Stahle, C. M.; Palmer, D.; Bartlett, L. M.; Parsons, A.; Shi, Zhiqing; Lisse, C. M.; Sappington, C.; Cao, N.; Shu, P.; Gehrels, N.; Teegarden, B.; Birsa, F.; Singh, S.; Odom, J.; Hanchak, C.; Tueller, J.; Barthelmy, S.; Krizmanic, J.; Barbier, L.

    A CdZnTe detector array is being developed for the proposed gamma-ray Burst ArcSecond Imaging and Spectroscopy (BASIS) spaceflight mission to accurately locate gamma-ray bursts, determine their distance scale, and measure the physical characteristics of the emission region. Two-dimensional strip detectors with 100 μm pitch have been fabricated and wire bonded to readout electronics to demonstrate the ability to localize 60 and 122 keV gamma-rays to less than 100 μm. Radiation damage studies on a CdZnTe detector exposed to MeV neutrons showed a small amount of activation but no detector performance degradation for fluences up to 1010 neutrons/cm2. A 1 × 1 in. CdZnTe detector has also been flown on a balloon payload at 115 000 ft in order to measure the CdZnTe background rates.

  19. The Effect of Twin Boundaries on the Spectroscopic Performance of CdZnTe Detectors

    NASA Technical Reports Server (NTRS)

    Parker, Bradford H.; Stahle, C. M.; Roth, D.; Babu, S.; Tueller, Jack; Powers, Edward I. (Technical Monitor)

    2001-01-01

    Most single grains in cadmium zinc telluride (CdZnTe) grown by the high-pressure Bridgman (HPB) technique contain multiple twin boundaries. As a consequence, twin boundaries are one of the most common macroscopic material defects found in large area (400 to 700 sq mm) CdZnTe specimens obtained from HPB ingots. Due to the prevalence of twin boundaries, understanding their effect on detector performance is key to the material selection process. Twin boundaries in several 2 mm thick large area specimens were first, documented using infrared transmission imaging. These specimens were then fabricated into either 2 mm pixel or planar detectors in order to examine the effect of the twin boundaries on detector performance. Preliminary results show that twin boundaries, which are decorated with tellurium inclusions, produce a reduction in detector efficiency and a degradation in resolution. The extent of the degradation appears to be a function of the density of tellurium inclusions.

  20. Response of CdZnTe Detectors on the Swift Burst Alert Telescope

    NASA Astrophysics Data System (ADS)

    Suzuki, M.; Tashiro, M.

    Swift (Gehrels, 2000) is the Gamma Ray Bursts (GRBs) explorer, that is scheduled for launch in 2004. The Swift's major instrument Burst Alert Telescope (BAT) detector array sits Cadmium Zinc Telluride (CdZnTe, CZT) semiconductor devices under a coded mask. The array has 32,768 individual Cd0.9Zn0.1Te1.0 detectors (4 × 4 mm^2 large, 2mm thick) that have a total detector area of 5240 cm^2. CdZnTe materials are able to operate at room temperature for its large band gap, and also have a high average atomic number which makes them sensitive to hard X-rays (15 ˜ 150 keV). We investigate energy response of the BAT detector for which to dedicate spectroscopy and imaging in observations of GRBs.

  1. Design and study of a coplanar grid array CdZnTe detector for improved spatial resolution.

    PubMed

    Ma, Yuedong; Xiao, Shali; Yang, Guoqiang; Zhang, Liuqiang

    2014-12-01

    Coplanar grid (CPG) CdZnTe detectors have been used as gamma-ray spectrometers for years. Comparing with pixelated CdZnTe detectors, CPG CdZnTe detectors have either no or poor spatial resolution, which directly limits its use in imaging applications. To address the issue, a 2×2 CPG array CdZnTe detector with dimensions of 7×7×5mm(3) was fabricated. Each of the CPG pairs in the detector was moderately shrunk in size and precisely designed to improve the spatial resolution while maintaining good energy resolution, considering the charge loss at the surface between the strips of each CPG pairs. Preliminary measurements were demonstrated at an energy resolution of 2.7-3.9% for the four CPG pairs using 662keV gamma rays and with a spatial resolution of 3.3mm, which is the best spatial resolution ever achieved for CPG CdZnTe detectors. The results reveal that the CPG CdZnTe detector can also be applied to imaging applications at a substantially higher spatial resolution.

  2. De-polarization of a CdZnTe radiation detector by pulsed infrared light

    SciTech Connect

    Dědič, V. Franc, J.; Rejhon, M.; Grill, R.; Zázvorka, J.; Sellin, P. J.

    2015-07-20

    This work is focused on a detailed study of pulsed mode infrared light induced depolarization of CdZnTe detectors operating at high photon fluxes. This depolarizing effect is a result of the decrease of positive space charge that is caused by the trapping of photogenerated holes at a deep level. The reduction in positive space charge is due to the optical transition of electrons from a valence band to the deep level due to additional infrared illumination. In this paper, we present the results of pulse mode infrared depolarization, by which it is possible to keep the detector in the depolarized state during its operation. The demonstrated mechanism represents a promising way to increase the charge collection efficiency of CdZnTe X-ray detectors operating at high photon fluxes.

  3. Surface Passivation of CdZnTe Detector by Hydrogen Peroxide Solution Etching

    NASA Technical Reports Server (NTRS)

    Hayes, M.; Chen, H.; Chattopadhyay, K.; Burger, A.; James, R. B.

    1998-01-01

    The spectral resolution of room temperature nuclear radiation detectors such as CdZnTe is usually limited by the presence of conducting surface species that increase the surface leakage current. Studies have shown that the leakage current can be reduced by proper surface preparation. In this study, we try to optimize the performance of CdZnTe detector by etching the detector with hydrogen peroxide solution as function of concentration and etching time. The passivation effect that hydrogen peroxide introduces have been investigated by current-voltage (I-V) measurement on both parallel strips and metal-semiconductor-metal configurations. The improvements on the spectral response of Fe-55 and 241Am due to hydrogen peroxide treatment are presented and discussed.

  4. Measurements on the spectroscopic performance of CdZnTe coplanar grid detectors.

    PubMed

    Yücel, H; Uyar, E; Esen, A N

    2012-08-01

    A performance study was performed for CdZnTe coplanar grid (CPG) detectors when used as γ-ray spectrometers. The detectors have the crystal volumes of 1, 1.6875 and 2.25 cm(3), respectively. Time stability of each CdZnTe CPG detector was investigated in a long-term operation (time span of 0.25 to about 100 h). The spectroscopic performances were measured at different bias voltages and at various photon energies ranging from 59.6 keV ((241)Am) to 1332.5 keV ((60)Co) for each detector, and evaluated by using the following parameters: energy resolution in FWHM, peak tailing in peak-to-valley (P/V) ratio and in FWHM/FW.25 M ratio, and photofraction using the acquired γ-ray spectra. No polarization effect was observed in terms of count rate, energy resolution and peak centroid shift. The obtained results indicate that better time stability and excellent spectroscopic performances of the present CdZnTe CPG detectors are shown for a room temperature γ-ray spectroscopy. PMID:22738836

  5. Direct measurement of mammographic x-ray spectra using a CdZnTe detector.

    PubMed

    Matsumoto, M; Yamamoto, A; Honda, I; Taniguchi, A; Kanamori, H

    2000-07-01

    Our purpose is to directly measure mammographic x-ray spectra with collimators and a low-efficiency CdZnTe detector developed recently and to find out the best fit response function of CdZnTe detector to correct the measured spectra. Photon spectra (target Mo or Rh) produced by a mammographic x-ray unit at 25-32 kV and 240 mAs (= 3 times of 80 mAs) and transmitted through 0.03 mm Mo or 0.025 mm Rh filter and object (0.1 mm Al to 0.8 mm Al phantoms) have been analyzed. Since detected spectra were distorted by the response of CdZnTe detector and did not present the true photon spectra, the correction was applied by the stripping procedure. The response function of detector used in this procedure has been determined by the evaluation of interactions (K-escape, coherent scattering, and Compton scattering processes) and incomplete charge collection calculated using the Monte Carlo method. We have used Kalpha1, Kalpha2, Kbeta1, Kbeta2 radiations of Cd, Zn, and Te, respectively and have used the weight function for the incomplete charge collection and have considered Compton scattering. The Monte Carlo simulations were continued by changing the important factors (mean path length of hole lambda(h), dead layer of the CZT crystal and weight factor Wq) of incomplete charge collection until the best fit response function was found out. Corrected photon spectra were compared with the mammographic x-ray spectral data of Bureau of Radiological Health (BRH) measured using a Ge detector. Attenuation curves of aluminum for 25-32 kV were calculated from the corrected photon spectra and compared with the attenuation curves measured using an ionization chamber. These results obtained using the CdZnTe detector agreed with the mammographic x-ray spectral data of BRH and attenuation curves obtained by the ionization chamber.

  6. Chemical etching and post-annealing for high performance CdZnTe strip detectors

    SciTech Connect

    Shi, Z.Q.; Stahle, C.M.; Shu, P.

    1998-12-31

    One of the critical issues in CdZnTe detector fabrication is the surface treatment. This will not only affect the electrical properties, such as leakage current, but also influence the physical properties, such as smoothness and adhesion between the metal and the semiconductor. The latter will determine the wire bonding yield. Historically, there has been a problem in achieving both low leakage current and excellent wire bonding yield. In this paper, the authors report their new approach to fabricate high performance doubled sided CdZnTe strip detectors. The new surface treatments involve chemical etching and post-annealing. The leakage current, interstrip resistance and energy resolution were studied as a function of different etchants/time and post-annealing temperature. It was found that a chemical etch with bromine in ethylene glycol (Br/EG) is suitable for the double sided strip detector process. Keeping a relatively smooth surface is critical for achieving a high yield of good strips. To improve the adhesion of the metal to CdZnTe for wire bonding, the detectors were annealed from 100 to 175 C for 10 hours. It has been observed that after annealing, not only has the strip leakage current decreased, but the interstrip resistance is increased for a temperature less than 150 C.

  7. A pixellated γ-camera based on CdTe detectors clinical interests and performances

    NASA Astrophysics Data System (ADS)

    Chambron, J.; Arntz, Y.; Eclancher, B.; Scheiber, Ch; Siffert, P.; Hage Hali, M.; Regal, R.; Kazandjian, A.; Prat, V.; Thomas, S.; Warren, S.; Matz, R.; Jahnke, A.; Karman, M.; Pszota, A.; Nemeth, L.

    2000-07-01

    A mobile gamma camera dedicated to nuclear cardiology, based on a 15 cm×15 cm detection matrix of 2304 CdTe detector elements, 2.83 mm×2.83 mm×2 mm, has been developed with a European Community support to academic and industrial research centres. The intrinsic properties of the semiconductor crystals - low-ionisation energy, high-energy resolution, high attenuation coefficient - are potentially attractive to improve the γ-camera performances. But their use as γ detectors for medical imaging at high resolution requires production of high-grade materials and large quantities of sophisticated read-out electronics. The decision was taken to use CdTe rather than CdZnTe, because the manufacturer (Eurorad, France) has a large experience for producing high-grade materials, with a good homogeneity and stability and whose transport properties, characterised by the mobility-lifetime product, are at least 5 times greater than that of CdZnTe. The detector matrix is divided in 9 square units, each unit is composed of 256 detectors shared in 16 modules. Each module consists in a thin ceramic plate holding a line of 16 detectors, in four groups of four for an easy replacement, and holding a special 16 channels integrated circuit designed by CLRC (UK). A detection and acquisition logic based on a DSP card and a PC has been programmed by Eurorad for spectral and counting acquisition modes. Collimators LEAP and LEHR from commercial design, mobile gantry and clinical software were provided by Siemens (Germany). The γ-camera head housing, its general mounting and the electric connections were performed by Phase Laboratory (CNRS, France). The compactness of the γ-camera head, thin detectors matrix, electronic readout and collimator, facilitates the detection of close γ sources with the advantage of a high spatial resolution. Such an equipment is intended to bedside explorations. There is a growing clinical requirement in nuclear cardiology to early assess the extent of an

  8. Electroless gold contact deposition on CdZnTe detectors by scanning pipette technique

    NASA Astrophysics Data System (ADS)

    Zambelli, N.; Marchini, L.; Benassi, G.; Calestani, D.; Caroli, E.; Zappettini, A.

    2012-08-01

    Gold electroless contacts are commonly used for the preparation of CdZnTe-based detectors. In this work it is shown that it is possible to deposit electroless patterned contacts on CdZnTe detectors without the use of photolithography by means of the scanning pipette technique. The technique is based on the delivery of gold chloride solution by means of a pipette moved by micro-controlled motors. The obtained detectors show optimal current-voltage characteristics and good spectroscopic response.

  9. CdZnTe Image Detectors for Hard-X-Ray Telescopes

    NASA Technical Reports Server (NTRS)

    Chen, C. M. Hubert; Cook, Walter R.; Harrison, Fiona A.; Lin, Jiao Y. Y.; Mao, Peter H.; Schindler, Stephen M.

    2005-01-01

    Arrays of CdZnTe photodetectors and associated electronic circuitry have been built and tested in a continuing effort to develop focal-plane image sensor systems for hard-x-ray telescopes. Each array contains 24 by 44 pixels at a pitch of 498 m. The detector designs are optimized to obtain low power demand with high spectral resolution in the photon- energy range of 5 to 100 keV. More precisely, each detector array is a hybrid of a CdZnTe photodetector array and an application-specific integrated circuit (ASIC) containing an array of amplifiers in the same pixel pattern as that of the detectors. The array is fabricated on a single crystal of CdZnTe having dimensions of 23.6 by 12.9 by 2 mm. The detector-array cathode is a monolithic platinum contact. On the anode plane, the contact metal is patterned into the aforementioned pixel array, surrounded by a guard ring that is 1 mm wide on three sides and is 0.1 mm wide on the fourth side so that two such detector arrays can be placed side-by-side to form a roughly square sensor area with minimal dead area between them. Figure 1 shows two anode patterns. One pattern features larger pixel anode contacts, with a 30-m gap between them. The other pattern features smaller pixel anode contacts plus a contact for a shaping electrode in the form of a grid that separates all the pixels. In operation, the grid is held at a potential intermediate between the cathode and anode potentials to steer electric charges toward the anode in order to reduce the loss of charges in the inter-anode gaps. The CdZnTe photodetector array is mechanically and electrically connected to the ASIC (see Figure 2), either by use of indium bump bonds or by use of conductive epoxy bumps on the CdZnTe array joined to gold bumps on the ASIC. Hence, the output of each pixel detector is fed to its own amplifier chain.

  10. Fluctuations in induced charge introduced by Te inclusions within CdZnTe radiation detectors

    SciTech Connect

    Bale, Derek S.

    2010-07-15

    Recently, homogenization theory based on a multiple-scale perturbation of the electron transport equation has been used to derive a mathematical framework for modeling the excess charge lost to Te inclusions within radiation detectors based on semi-insulating cadmium zinc telluride (CdZnTe). In that theory, the heterogeneous material is mathematically replaced by a homogenized CdZnTe crystal whose effective electron attenuation length incorporates the additional uniform electron trapping caused by the inclusions. In this paper, the homogenization theory is extended to incorporate fluctuations in the induced charge (i.e., charge collection nonuniformities) introduced by the random position and size distributions of a noncorrelated population of small (i.e, <20 {mu}m) Te inclusions. Analysis of the effective parameters derived within the homogenized framework is used to develop a probability distribution of effective electron attenuation lengths, and therefore effective mobility-lifetime products, as a function of both the position and size distribution of Te inclusions. Example distributions are detailed for the case of an exponential size distribution at various number densities. Further, it is demonstrated that the inclusion-induced material nonuniformities derived in this paper can be numerically sampled efficiently, making them applicable to Monte Carlo device simulation of realistic CdZnTe detectors. Simulated charge induction maps and pulse-height spectra are presented and compared to recently published measurements.

  11. Growth of CdZnTe Crystals for Radiation Detector Applications by Directional Solidification

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua

    2014-01-01

    Advances in Cadmium Zinc Telluride (Cd(sub 1-x)Zn(sub x)Te) growth techniques are needed for the production of large-scale arrays of gamma and x-ray astronomy. The research objective is to develop crystal growth recipes and techniques to obtain large, high quality CdZnTe single crystal with reduced defects, such as charge trapping, twinning, and tellurium precipitates, which degrade the performance of CdZnTe and, at the same time, to increase the yield of usable material from the CdZnTe ingot. A low gravity material experiment, "Crystal Growth of Ternary Compound Semiconductors in Low Gravity Environment", will be performed in the Material Science Research Rack (MSRR) on International Space Station (ISS). One section of the flight experiment is the melt growth of CdZnTe ternary compounds. This talk will focus on the ground-based studies on the growth of Cd(sub 0.80)Zn(sub 0.20)Te crystals for radiation detector applications by directional solidification. In this investigation, we have improved the properties that are most critical for the detector applications (electrical properties and crystalline quality): a) Electrical resistivity: use high purity starting materials (with reproducible impurity levels) and controlled Cd over pressure during growth to reproducibly balance the impurity levels and Cd vacancy concentration b) Crystalline quality: use ultra-clean growth ampoule (no wetting after growth), optimized thermal profile and ampoule design, as well as a technique for supercool reduction to growth large single crystal with high crystalline quality

  12. CDZNTE ROOM-TEMPERATURE SEMICONDUCTOR GAMMA-RAY DETECTOR FOR NATIONAL-SECURITY APPLICATIONS.

    SciTech Connect

    CAMARDA,G.S.; BOLOTNIKOV, A.E.; CUI, Y.; HOSSAIN, A.; KOHMAN, K.T.; JAMES, R.B.

    2007-05-04

    One important mission of the Department of Energy's National Nuclear Security Administration is to develop reliable gamma-ray detectors to meet the widespread needs of users for effective techniques to detect and identify special nuclear- and radioactive-materials. Accordingly, the Nonproliferation and National Security Department at Brookhaven National Laboratory was tasked to evaluate existing technology and to develop improved room-temperature detectors based on semiconductors, such as CdZnTe (CZT). Our research covers two important areas: Improving the quality of CZT material, and exploring new CZT-based gamma-ray detectors. In this paper, we report on our recent findings from the material characterization and tests of actual CZT devices fabricated in our laboratory and from materials/detectors supplied by different commercial vendors. In particular, we emphasize the critical role of secondary phases in the current CZT material and issues in fabricating the CZT detectors, both of which affect their performance.

  13. Preliminary Performance of CdZnTe Imaging Detector Prototypes

    NASA Technical Reports Server (NTRS)

    Ramsey, B.; Sharma, D. P.; Meisner, J.; Gostilo, V.; Ivanov, V.; Loupilov, A.; Sokolov, A.; Sipila, H.

    1999-01-01

    The promise of good energy and spatial resolution coupled with high efficiency and near-room-temperature operation has fuelled a large International effort to develop Cadmium-Zinc-Telluride (CdZnTe) for the hard-x-ray region. We present here preliminary results from our development of small-pixel imaging arrays fabricated on 5x5x1-mm and 5x5x2-mm spectroscopy and discriminator-grade material. Each array has 16 (4x4) 0.65-mm gold readout pads on a 0.75-mm pitch, with each pad connected to a discrete preamplifier via a pulse-welded gold wire. Each array is mounted on a 3-stage Peltier cooler and housed in an ion-pump-evacuated housing which also contains a hybrid micro-assembly for the 16 channels of electronics. We have investigated the energy resolution and approximate photopeak efficiency for each pixel at several energies and have used an ultra-fine beam x-ray generator to probe the performance at the pixel boundaries. Both arrays gave similar results, and at an optimum temperature of -20 C we achieved between 2 and 3% FWHM energy resolution at 60 keV and around 15% at 5.9 keV. We found that all the charge was contained within 1 pixel until very close to the pixels edge, where it would start to be shared with its neighbor. Even between pixels, all the charge would be appropriately shared with no apparently loss of efficiency or resolution. Full details of these measurements will be presented, together with their implications for future imaging-spectroscopy applications.

  14. HAND-HELD GAMMA-RAY SPECTROMETER BASED ON HIGH-EFFICIENCY FRISCH-RING CdZnTe DETECTORS.

    SciTech Connect

    CUI,Y.

    2007-05-01

    Frisch-ring CdZnTe detectors have demonstrated good energy resolution, el% FWHM at 662 keV, and good efficiency for detecting gamma rays. This technique facilitates the application of CdZnTe materials for high efficiency gamma-ray detection. A hand-held gamma-ray spectrometer based on Frisch-ring detectors is being designed at Brookhaven National Laboratory. It employs an 8x8 CdZnTe detector array to achieve a high volume of 19.2 cm3, so that detection efficiency is significantly improved. By using the front-end ASICs developed at BNL, this spectrometer has a small profile and high energy resolution. The spectrometer includes signal processing circuit, digitization and storage circuit, high-voltage module, and USB interface. In this paper, we introduce the details of the system structure and report our test results with it.

  15. Hand-Held Gamma-Ray Spectrometer Based on High-Efficiency Frisch-Ring Cdznte Detectors

    SciTech Connect

    Cui, Y.; Bolotnikov, A; Camarda, G; Hossain, A; James, R; DeGeronimo, G; Fried, J; O'Connor, P; Kargar, A; et. al.

    2008-01-01

    Frisch-ring CdZnTe detectors have demonstrated both good energy resolution, <1% FWHM at 662 keV, and good efficiency in detecting gamma rays, highlighting the strong potential of CdZnTe materials for such applications. We are designing a hand-held gamma-ray spectrometer based on Frisch-ring detectors at Brookhaven National Laboratory. It employs an 8 times 8 CdZnTe detector array to achieve a high volume of 19.2 cm3, so greatly improving detection efficiency. By using the front-end application-specific integrated circuits (ASICs) developed at BNL, this spectrometer has a small profile and high energy-resolution. It includes a signal processing circuit, digitization and storage circuits, a high-voltage module, and a universal serial bus (USB) interface. In this paper, we detail the system's structure and report the results of our tests with it.

  16. CdZnTe x-ray detector for 30 {endash} 100 keV energy

    SciTech Connect

    Yoo, S.-S.; Rodricks, B.; Shastri, S.D.; Montano, P.A.

    1996-07-01

    High-pressure-Bridgman (HPB) grown CdZnTe x-ray detectors 1.25-1.7 mm thick were tested using monochromatic x-rays of 30 to 100 keV generated by a high energy x-ray generator. The results were compared with a commercially available 5 cm thick NaI detector. A linear dependence of the counting rate versus the x-ray generator tube current was observed at 58.9 keV. The measured pulse height of the photopeaks shows a linear dependence on energy. Electron and hole mobility-lifetime products ({mu}{tau}) were deduced by fitting bias dependent photopeak channel numbers at 30 keV x-ray energy. Values of 2 x 10{sup -3} cm{sup 2}/V and 2 x 10{sup -4}cm{sup 2}/V were obtained for {mu}{tau}{sub e} and {mu}{tau}{sub p}, respectively. The detector efficiency of CdZnTe at a 100 V bias was as high as, or higher than 90 % compared to a NaI detector. At x-ray energies higher than 70 keV, the detection efficiency becomes a dominant factor and decreases to 75 % at 100 keV.

  17. Investigation of the limitations of the highly pixilated CdZnTe detector for PET applications

    PubMed Central

    Komarov, Sergey; Yin, Yongzhi; Wu, Heyu; Wen, Jie; Krawczynski, Henric; Meng, Ling-Jian; Tai, Yuan-Chuan

    2016-01-01

    We are investigating the feasibility of a high resolution positron emission tomography (PET) insert device based on the CdZnTe detector with 350 μm anode pixel pitch to be integrated into a conventional animal PET scanner to improve its image resolution. In this paper, we have used a simplified version of the multi pixel CdZnTe planar detector, 5 mm thick with 9 anode pixels only. This simplified 9 anode pixel structure makes it possible to carry out experiments without a complete application-specific integrated circuits readout system that is still under development. Special attention was paid to the double pixel (or charge sharing) detections. The following characteristics were obtained in experiment: energy resolution full-width-at-half-maximum (FWHM) is 7% for single pixel and 9% for double pixel photoelectric detections of 511 keV gammas; timing resolution (FWHM) from the anode signals is 30 ns for single pixel and 35 ns for double pixel detections (for photoelectric interactions only the corresponding values are 20 and 25 ns); position resolution is 350 μm in x,y-plane and ~0.4 mm in depth-of-interaction. The experimental measurements were accompanied by Monte Carlo (MC) simulations to find a limitation imposed by spatial charge distribution. Results from MC simulations suggest the limitation of the intrinsic spatial resolution of the CdZnTe detector for 511 keV photoelectric interactions is 170 μm. The interpixel interpolation cannot recover the resolution beyond the limit mentioned above for photoelectric interactions. However, it is possible to achieve higher spatial resolution using interpolation for Compton scattered events. Energy and timing resolution of the proposed 350 μm anode pixel pitch detector is no better than 0.6% FWHM at 511 keV, and 2 ns FWHM, respectively. These MC results should be used as a guide to understand the performance limits of the pixelated CdZnTe detector due to the underlying detection processes, with the understanding of

  18. Direct conversion Si and CdZnTe detectors for digital mammography

    NASA Astrophysics Data System (ADS)

    Yin, Shi; Tümer, Tümay O.; Maeding, Dale; Mainprize, James; Mawdsley, Gord; Yaffe, Martin J.; Gordon, Eli E.; Hamilton, William J.

    2000-07-01

    Hybrid pixel detector arrays that convert X-rays directly into charge signals are under development at NOVA for application to digital mammography. This technology also has wide application possibilities in other fields of radiology or in industrial imaging, nondestructive evaluation (NDE) and nondestructive inspection (NDI). These detectors have potentially superior properties compared to either emulsion-based film-screen systems which has nonlinear response to X-rays, or phosphor-based detectors in which there is an intermediate step of X-ray to light photon conversion (Feig and Yaffe, Radiol. Clinics North America 33 (1995) 1205-1230). Potential advantages of direct conversion detectors are high quantum efficiencies (QE) of 98% or higher (for 0.3 mm thick CdZnTe detector with 20 keV X-rays), improved contrast, high sensitivity and low intrinsic noise. These factors are expected to contribute to high detective quantum efficiency (DQE). The prototype hybrid pixel detector developed has 50×50 μm pixel size, and is designed to have linear response to X-rays, and can support a dynamic range up to 14 bits. Modulation Transfer Function (MTF) is measured on a 1-mm silicon detector system where 10% or better modulations are obtained at 10 lp/mm spatial frequency. Preliminary DQE measurements of the same detector yields a value of 75% at zero spatial frequency. In this paper, we report results obtained from our first full size prototype readout ASIC chips hybridized with both silicon and CdZnTe detector arrays and present preliminary MTF and DQE measurement results as well as some test images.

  19. Progress in the Development of CdZnTe Unipolar Detectors for Different Anode Geometries and Data Corrections

    PubMed Central

    Zhang, Qiushi; Zhang, Congzhe; Lu, Yanye; Yang, Kun; Ren, Qiushi

    2013-01-01

    CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques. PMID:23429509

  20. Isotope identification software for Gamma spectra taken with CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Brutscher, J.; Arlt, R.; Czock, K. H.

    2001-02-01

    The identification of isotopes in a sample emitting gamma rays is a complex and difficult task particularly if the number of gamma lines is high, detector resolution and statistics are limited and little is known about the history of the sample. The better the resolution the easier this task can be accomplished. High-purity germanium detectors (HPGe) are in this respect the best choice, however, they are difficult to use under field conditions and in spent fuel ponds, since they require liquid nitrogen for cooling. NaI detectors do not require cooling, but have limitations in their resolution. For field applications, e.g., the verification of nuclear material, the use of CdZnTe detectors has advantages over NaI detectors since their resolution is much better. CdZnTe detectors, often exhibit asymmetric peak shapes, particularly at high energies making automated peak fitting methods and sophisticated isotope identification programs difficult to use. In this paper the design and use of a semi-automated isotope identification program is described. It is based on an interactive graphical method to find a simple solution to identifying various isotopes which may be present in a sample. The spectrum to be analyzed and an isotopic library containing a list of suspected isotopes is loaded. After selection of detector type , measurement geometry and starting values for the resolution, a peak search is performed. This can also determine the FWHM of the gamma peaks as function of energy. For each gamma peak found, the software suggests possible candidate isotopes to which the gamma peak may belong. The next, most decisive step to determine to which of the sometimes many choices of isotopes, a certain gamma line belongs to, is visual and interactive. Once one candidate's gamma line is marked, the program overlays the expected gamma peak pattern of this isotope with the measured one. Based on the presence or absence of certain lines in the spectrum (checked visually, aided by a

  1. POLARIZATION STUDIES OF CdZnTe DETECTORS USING SYNCHROTRON X-RAY RADIATION.

    SciTech Connect

    CAMARDA,G.S.; BOLOTNIKOV, A.E.; CUI, Y.; HOSSAIN, A.; JAMES, R.B.

    2007-07-01

    New results on the effects of small-scale defects on the charge-carrier transport in single-crystal CdZnTe (CZT) material were produced. We conducted detailed studies of the role of Te inclusions in CZT by employing a highly collimated synchrotron x-ray radiation source available at Brookhaven's National Synchrotron Light Source (NSLS). We were able to induce polarization effects by irradiating specific areas with the detector. These measurements allowed the first quantitative comparison between areas that are free of Te inclusions and those with a relatively high concentration of inclusions. The results of these polaration studies will be reported.

  2. Analysis of trapping and de-trapping in CdZnTe detectors by Pockels effect

    NASA Astrophysics Data System (ADS)

    Rejhon, M.; Franc, J.; Dědič, V.; Kunc, J.; Grill, R.

    2016-09-01

    In this contribution we introduce a method of deep level spectroscopy in semi-insulating semiconductors demonstrated on detector-grade bulk CdZnTe. The method is based on the measurements of temporal and temperature evolution of the electric field profile in studied samples, which is very sensitive to a change of occupancy of deep levels. The measurement of the electric field is based on the linear electro-optic (Pockels) effect using the InGaAs avalanche photodiode with fast response. The internal electric field profile in studied samples significantly changes under various external conditions represented by the application of the bias and pulsed illumination with below-bandgap light. From the knowledge of the electric field behavior and using a standard analysis based on thermally induced transitions of electrons and holes from the deep levels to the conduction and valence bands, respectively, it is possible to get activation energies of the energy levels, their types (donor or acceptor) and corresponding capture cross-sections. By this method we have found deep levels responsible for the polarization of CdZnTe detector under high photon-fluxes. Identified deep levels {{E}\\text{v}}+0.41 eV, {{E}\\text{v}}+0.77 eV and {{E}\\text{v}}+0.94 eV can capture the photo-generated holes and thus form a positive space charge, which is responsible for polarization of the detector.

  3. EFFECT OF SURFACE PREPARATION TECHNIQUE ON THE RADIATION DETECTOR PERFORMANCEOF CDZNTE

    SciTech Connect

    Duff, M

    2007-05-23

    Synthetic CdZnTe (CZT) semiconducting crystals are highly suitable for the room temperature-based detection of gamma radiation. The surface preparation of Au contacts on surfaces of CZT detectors is typically conducted after (1) polishing to remove artifacts from crystal sectioning and (2) chemical etching, which removes residual mechanical surface damage however etching results in a Te rich surface layer that is prone to oxidize. Our studies show that CZT surfaces that are only polished (as opposed to polished and etched) can be contacted with Au and will yield lower surface currents. Due to their decreased dark currents, these as-polished surfaces can be used in the fabrication of gamma detectors exhibiting a higher performance than polished and etched surfaces with relatively less peak tailing and greater energy resolution. CdZnTe or ''CZT'' crystals are attractive to use in homeland security applications because they detect radiation at room temperature and do not require low temperature cooling as with silicon- and germanium-based detectors. Relative to germanium and silicon detectors, CZT is composed of higher Z elements and has a higher density, which gives it greater ''stopping power'' for gamma rays making a more efficient detector. Single crystal CZT materials with high bulk resistivity ({rho}>10{sup 10} {Omega} x cm) and good mobility-lifetime products are also required for gamma-ray spectrometric applications. However, several factors affect the detector performance of CZT are inherent to the as grown crystal material such as the presence of secondary phases, point defects and the presence of impurities (as described in a literature review by R. James and researchers). These and other factors can limit radiation detector performance such as low resistivity, which causes a large electronic noise and the presence of traps and other heterogeneities, which result in peak tailing and poor energy resolution.

  4. Analysis of Surface Chemistry and Detector Performance of Chemically Process CdZnTe crystals

    SciTech Connect

    HOSSAIN, A.; Yang, G.; Sutton, J.; Zergaw, T.; Babalola, O. S.; Bolotnikov, A. E.; Camarda. ZG. S.; Gul, R.; Roy, U. N., and James, R. B.

    2015-10-05

    The goal is to produce non-conductive smooth surfaces for fabricating low-noise and high-efficiency CdZnTe devices for gamma spectroscopy. Sample preparation and results are discussed. The researachers demonstrated various bulk defects (e.g., dislocations and sub-grain boundaries) and surface defects, and examined their effects on the performance of detectors. A comparison study was made between two chemical etchants to produce non-conductive smooth surfaces. A mixture of bromine and hydrogen peroxide proved more effective than conventional bromine etchant. Both energy resolution and detection efficiency of CZT planar detectors were noticeably increased after processing the detector crystals using improved chemical etchant and processing methods.

  5. Characterization of M-π-n CdTe pixel detectors coupled to HEXITEC readout chip

    NASA Astrophysics Data System (ADS)

    Veale, M. C.; Kalliopuska, J.; Pohjonen, H.; Andersson, H.; Nenonen, S.; Seller, P.; Wilson, M. D.

    2012-01-01

    Segmentation of the anode-side of an M-π-n CdTe diode, where the pn-junction is diffused into the detector bulk, produces large improvements in the spatial and energy resolution of CdTe pixel detectors. It has been shown that this fabrication technique produces very high inter-pixel resistance and low leakage currents are obtained by physical isolation of the pixels of M-π-n CdTe detectors. In this paper the results from M-π-n CdTe detectors stud bonded to a spectroscopic readout ASIC are reported. The CdTe pixel detectors have 250 μm pitch and an area of 5 × 5 mm2 with thicknesses of 1 and 2 mm. The polarization and energy resolution dependence of the M-π-n CdTe detectors as a function of detector thickness are discussed.

  6. Nuclear reactor pulse tracing using a CdZnTe electro-optic radiation detector

    NASA Astrophysics Data System (ADS)

    Nelson, Kyle A.; Geuther, Jeffrey A.; Neihart, James L.; Riedel, Todd A.; Rojeski, Ronald A.; Ugorowski, Philip B.; McGregor, Douglas S.

    2012-07-01

    CdZnTe has previously been shown to operate as an electro-optic radiation detector by utilizing the Pockels effect to measure steady-state nuclear reactor power levels. In the present work, the detector response to reactor power excursion experiments was investigated. Peak power levels during an excursion were predicted to be between 965 MW and 1009 MW using the Fuchs-Nordheim and Fuchs-Hansen models and confirmed with experimental data from the Kansas State University TRIGA Mark II nuclear reactor. The experimental arrangement of the Pockels cell detector includes collimated laser light passing through a transparent birefringent crystal, located between crossed polarizers, and focused upon a photodiode. The birefringent crystal, CdZnTe in this case, is placed in a neutron beam emanating from a nuclear reactor beam port. After obtaining the voltage-dependent Pockels characteristic response curve with a photodiode, neutron measurements were conducted from reactor pulses with the Pockels cell set at the 1/4 and 3/4 wave bias voltages. The detector responses to nuclear reactor pulses were recorded in real-time using data logging electronics, each showing a sharp increase in photodiode current for the 1/4 wave bias, and a sharp decrease in photodiode current for the 3/4 wave bias. The polarizers were readjusted to equal angles in which the maximum light transmission occurred at 0 V bias, thereby, inverting the detector response to reactor pulses. A high sample rate oscilloscope was also used to more accurately measure the FWHM of the pulse from the electro-optic detector, 64 ms, and is compared to the experimentally obtained FWHM of 16.0 ms obtained with the 10B-lined counter.

  7. New room temperature high resolution solid-state detector (CdZnTe) for hard x rays and gamma rays

    NASA Technical Reports Server (NTRS)

    Stewart, Amyelizabeth C.; Desai, Upendra D.

    1993-01-01

    The new CdZnTe high 'Z' material represents a significant improvement in detectors for high energy photons. With the thicknesses available, photons up to 100 keV can be efficiently detected. This material has a wide band gap of 1.5 - 2.2 eV which allows it to operate at room temperature while providing high spectral resolution. Results of resolution evaluations are presented. This detector can be used for high resolution spectral measurements of photons in x-ray and gamma-ray astronomy, offering a significant reduction in the weight, power, and volume of the detector system compared to more conventional detector types such as scintillation counters. In addition, the detector will have the simplicity and reliability of solid-state construction. The CdZnTe detector, as a new development, has not yet been evaluated in space. The Get Away Special program can provide this opportunity.

  8. Charge-sensitive front-end electronics with operational amplifiers for CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Födisch, P.; Berthel, M.; Lange, B.; Kirschke, T.; Enghardt, W.; Kaever, P.

    2016-09-01

    Cadmium zinc telluride (CdZnTe, CZT) radiation detectors are suitable for a variety of applications, due to their high spatial resolution and spectroscopic energy performance at room temperature. However, state-of-the-art detector systems require high-performance readout electronics. Though an application-specific integrated circuit (ASIC) is an adequate solution for the readout, requirements of high dynamic range and high throughput are not available in any commercial circuit. Consequently, the present study develops the analog front-end electronics with operational amplifiers for an 8×8 pixelated CZT detector. For this purpose, we modeled an electrical equivalent circuit of the CZT detector with the associated charge-sensitive amplifier (CSA). Based on a detailed network analysis, the circuit design is completed by numerical values for various features such as ballistic deficit, charge-to-voltage gain, rise time, and noise level. A verification of the performance is carried out by synthetic detector signals and a pixel detector. The experimental results with the pixel detector assembly and a 22Na radioactive source emphasize the depth dependence of the measured energy. After pulse processing with depth correction based on the fit of the weighting potential, the energy resolution is 2.2% (FWHM) for the 511 keV photopeak.

  9. The polarization mechanism in CdTe Schottky detectors

    SciTech Connect

    Cola, Adriano; Farella, Isabella

    2009-03-09

    Schottky CdTe nuclear detectors are affected by bias-induced polarization phenomena when operating at room temperature. A space charge buildup occurs at the blocking contact causing the degradation in detection performance. By means of Pockels effect, we study the electric field distribution inside the detector and its variation with time and temperature. The analysis of the space charge has allowed us to point out the role of the Schottky contact and of carrier detrapping from deep levels in the polarization mechanism. Moreover, measured current transients have been quantitatively accounted for by the increase in the electric field at the blocking junction.

  10. SemiSPECT: A Small-animal Imaging System Based on Eight CdZnTe Pixel Detectors

    PubMed Central

    Peterson, Todd E.; Kim, Hyunki; Crawford, Michael J.; Gershman, Benjamin M.; Hunter, William C.J.; Barber, H. Bradford; Furenlid, Lars R.; Wilson, Donald W.; Woolfenden, James M.; Barrett, Harrison H.

    2015-01-01

    We have constructed a SPECT system for small animals that utilizes eight CdZnTe pixel detectors. The eight detectors are arranged in a single octagonal ring, where each views the object to be imaged through a single pinhole. Additional projections are obtained via rotation of the animal. Each CdZnTe detector is approximately 2 mm in thickness and is patterned on one surface into a 64×64 array of pixels with 380 micron pitch. We have designed an electronic readout system capable of collecting data from the eight detectors in listmode. In this scheme each event entry for a gamma-ray hit includes the pulse height of the pixel with the largest signal and the pulse height for each of its eight nearest neighbors. We present details of the overall design, the electronics, and system performance. PMID:26568674

  11. Effects of Te inclusions on the performance of CdZnTe radiation detectors

    SciTech Connect

    Bolotnikov,A.E.; Abdul-Jabber, N. M.; Babalola, O. S.; Camarda, G. S.; Cui, Y.; Hossain, A. M.; Jackson, E. M.; Jackson, H. C.; James, J. A.; Kohman, K. T.; Luryi, A. L.; James, R. B.

    2008-10-19

    Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beamline recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.

  12. Effect of Te Inclusions on the Performance of Cdznte Radiation Detectors

    SciTech Connect

    Bolotnikov, A.; Abdul-Jabbar, N; Babalola, O; Camarda, G; Cui, Y; Hossain, A; Jackson, E; Jackson, H; James, J; et. al.

    2009-01-01

    Te inclusions existing at high concentrations in CdZnTe (CZT) material can degrade the performance of CZT detectors. These microscopic defects trap the free electrons generated by incident radiation, so entailing significant fluctuations in the total collected charge and thereby strongly affecting the energy resolution of thick (long-drift) detectors. Such effects were demonstrated in thin planar detectors, and, in many cases, they proved to be the dominant cause of the low performance of thick detectors, wherein the fluctuations in the charge losses accumulate along the charge's drift path. We continued studying this effect using different tools and techniques. We employed a dedicated beamline recently established at BNL's National Synchrotron Light Source for characterizing semiconductor radiation detectors, along with an IR transmission microscope system, the combination of which allowed us to correlate the concentration of defects with the devices' performances. We present here our new results from testing over 50 CZT samples grown by different techniques. Our goals are to establish tolerable limits on the size and concentrations of these detrimental Te inclusions in CZT material, and to provide feedback to crystal growers to reduce their numbers in the material.

  13. Control of electric field in CdZnTe radiation detectors by above-bandgap light

    SciTech Connect

    Franc, J.; Dědič, V.; Rejhon, M.; Zázvorka, J.; Praus, P.; Touš, J.; Sellin, P. J.

    2015-04-28

    We have studied the possibility of above bandgap light induced depolarization of CdZnTe planar radiation detector operating under high flux of X-rays by Pockels effect measurements. In this contribution, we show a similar influence of X-rays at 80 kVp and LED with a wavelength of 910 nm irradiating the cathode on polarization of the detector due to an accumulation of a positive space charge of trapped photo-generated holes. We have observed the depolarization of the detector under simultaneous cathode-site illumination with excitation LED at 910 nm and depolarization above bandgap LED at 640 nm caused by trapping of drifting photo-generated electrons. Although the detector current is quite high during this depolarization, we have observed that it decreases relatively fast to its initial value after switching off the depolarizing light. In order to get detailed information about physical processes present during polarization and depolarization and, moreover, about associated deep levels, we have performed the Pockels effect infrared spectral scanning measurements of the detector without illumination and under illumination in polarized and optically depolarized states.

  14. CdZnTe detector in mammographic x-ray spectroscopy.

    PubMed

    Miyajima, Satoshi; Imagawa, Kotaro

    2002-11-21

    A CdZnTe (CZT) detector was utilized in mammographic x-ray spectroscopy under clinical conditions. First, the detector response was investigated using y-rays from 241Am. The escape of secondary (Compton scattered and K fluorescent) x-rays and tailing due to carrier trapping were minor in the mammographic energy range. In addition, the transmission of primary x-rays was minimal from the results calculated using the mass attenuation coefficients of CZT. Therefore, spectral distortion in this energy range was expected to be negligible. Secondly, x-ray spectroscopy was carried out with the CZT detector. The measured spectra were in good agreement with the spectra obtained with the Compton-scatter method with a high-purity germanium detector. Moreover, the half-value layers (HVLs) calculated from the CZT spectra were consistent with the HVLs measured with an ionization chamber. The results indicate that a CZT detector can be utilized in mammographic x-ray spectroscopy without any corrections.

  15. CdZnTe detector in mammographic x-ray spectroscopy

    NASA Astrophysics Data System (ADS)

    Miyajima, Satoshi; Imagawa, Kotaro

    2002-11-01

    A CdZnTe (CZT) detector was utilized in mammographic x-ray spectroscopy under clinical conditions. First, the detector response was investigated using γ-rays from 241Am. The escape of secondary (Compton scattered and K fluorescent) x-rays and tailing due to carrier trapping were minor in the mammographic energy range. In addition, the transmission of primary x-rays was minimal from the results calculated using the mass attenuation coefficients of CZT. Therefore, spectral distortion in this energy range was expected to be negligible. Secondly, x-ray spectroscopy was carried out with the CZT detector. The measured spectra were in good agreement with the spectra obtained with the Compton-scatter method with a high-purity germanium detector. Moreover, the half-value layers (HVLs) calculated from the CZT spectra were consistent with the HVLs measured with an ionization chamber. The results indicate that a CZT detector can be utilized in mammographic x-ray spectroscopy without any corrections.

  16. TE INCLUSIONS AND THEIR RELATIONSHIP TO THE PERFORMANCE OF CDZNTE DETECTORS.

    SciTech Connect

    CARINI, G.A.; BOLOTNIKOV, A.E.; CAMARDA, G.S.; CUI, Y.; JACKSON, H.; BURGER, A.; KOHMAN, K.T.; LI, L.; JAMES, R.B.

    2006-08-13

    Te-rich secondary phases existing in CdZnTe (CZT) single crystals degrade the spectroscopic performance of these detectors. An unpredictable number of charges are trapped, corresponding to the abundance of these microscopic defects, thereby leading to fluctuations in the total collected charge and strongly affecting the uniformity of charge-collection efficiency. These effects, observed in thin planar detectors, also were found to be the dominant cause of the low performance of thick detectors, wherein the fluctuations accumulate along the charge's drift path. Reducing the size of Te inclusions from a virtual diameter of 10-20 {micro}m down to less than 5 {micro}m already allowed us to produce Frisch-ring detectors with a resolution as good as {approx}0.8% FWHM at 662 keV: Understanding and modeling the mechanisms involving Te-rich secondary phases and charge loss requires systematic studies on a spatial scale never before realized. Here, we describe a dedicated beam-line recently established at BNL's National Synchrotron Light Source for characterizing semiconductor detectors along with a IR system with counting capability that permits us to correlate the concentration of defects with the devices' performances.

  17. Experimental study of double-{beta} decay modes using a CdZnTe detector array

    SciTech Connect

    Dawson, J. V.; Goessling, C.; Koettig, T.; Muenstermann, D.; Rajek, S.; Schulz, O.; Janutta, B.; Zuber, K.; Junker, M.; Reeve, C.; Wilson, J. R.

    2009-08-15

    An array of sixteen 1 cm{sup 3} CdZnTe semiconductor detectors was operated at the Gran Sasso Underground Laboratory (LNGS) to further investigate the feasibility of double-{beta} decay searches with such devices. As one of the double-{beta} decay experiments with the highest granularity the 4x4 array accumulated an overall exposure of 18 kg days. The setup and performance of the array is described. Half-life limits for various double-{beta} decay modes of Cd, Zn, and Te isotopes are obtained. No signal has been found, but several limits beyond 10{sup 20} years have been performed. They are an order of magnitude better than those obtained with this technology before and comparable to most other experimental approaches for the isotopes under investigation. An improved limit for the {beta}{sup +}/EC decay of {sup 120}Te is given.

  18. Application of CdZnTe Gamma-Ray Detector for Imaging Corrosion under Insulation

    NASA Astrophysics Data System (ADS)

    Abdullah, J.; Yahya, R.

    2007-05-01

    Corrosion under insulation (CUI) on the external wall of steel pipes is a common problem in many types of industrial plants. This is mainly due to the presence of moisture or water in the insulation materials. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often the result of localised corrosion and not general wasting over a large area. These failures can tee catastrophic in nature or at least have an adverse economic effect in terms of downtime and repairs. There are a number of techniques used today for CUI investigations. The main ones are profile radiography, pulse eddy current, ultrasonic spot readings and insulation removal. A new system now available is portable Pipe-CUI-Profiler. The nucleonic system is based on dual-beam gamma-ray absorption technique using Cadmium Zinc Telluride (CdZnTe) semiconductor detectors. The Pipe-CUI-Profiler is designed to inspect pipes of internal diameter 50, 65, 80, 90, 100, 125 and 150 mm. Pipeline of these sizes with aluminium or thin steel sheathing, containing fibreglass or calcium silicate insulation to thickness of 25, 40 and 50 mm can be inspected. The system has proven to be a safe, fast and effective method of inspecting pipe in industrial plant operations. This paper describes the application of gamma-ray techniques and CdZnTe semiconductor detectors in the development of Pipe-CUI-Profiler for non-destructive imaging of corrosion under insulation of steel pipes. Some results of actual pipe testing in large-scale industrial plant will be presented.

  19. Application of CdZnTe Gamma-Ray Detector for Imaging Corrosion under Insulation

    SciTech Connect

    Abdullah, J.; Yahya, R.

    2007-05-09

    Corrosion under insulation (CUI) on the external wall of steel pipes is a common problem in many types of industrial plants. This is mainly due to the presence of moisture or water in the insulation materials. This type of corrosion can cause failures in areas that are not normally of a primary concern to an inspection program. The failures are often the result of localised corrosion and not general wasting over a large area. These failures can tee catastrophic in nature or at least have an adverse economic effect in terms of downtime and repairs. There are a number of techniques used today for CUI investigations. The main ones are profile radiography, pulse eddy current, ultrasonic spot readings and insulation removal. A new system now available is portable Pipe-CUI-Profiler. The nucleonic system is based on dual-beam gamma-ray absorption technique using Cadmium Zinc Telluride (CdZnTe) semiconductor detectors. The Pipe-CUI-Profiler is designed to inspect pipes of internal diameter 50, 65, 80, 90, 100, 125 and 150 mm. Pipeline of these sizes with aluminium or thin steel sheathing, containing fibreglass or calcium silicate insulation to thickness of 25, 40 and 50 mm can be inspected. The system has proven to be a safe, fast and effective method of inspecting pipe in industrial plant operations. This paper describes the application of gamma-ray techniques and CdZnTe semiconductor detectors in the development of Pipe-CUI-Profiler for non-destructive imaging of corrosion under insulation of steel pipes. Some results of actual pipe testing in large-scale industrial plant will be presented.

  20. Rejecting incomplete charge-collection events in CdZnTe and other semiconductor detectors

    NASA Astrophysics Data System (ADS)

    Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; De Geronimo, G.; Fried, J.; Gul, R.; Hossain, A.; Kim, K.; Yang, G.; Vernon, E.; James, R. B.

    2012-02-01

    In an ideal single-carrier-type gamma ray detector, the amplitudes of the signals and the carrier drift times are correlated variables. However, if the charges produced by an incident photon are not fully collected, as is the case in CdZnTe detectors containing crystal defects, the above correlation does not hold. This permits the application of an event recognition algorithm to identify these incomplete charge collection (ICC) events, caused by the "bad" regions inside a detector, so that they can be removed from pulse height spectra. The ICC events primarily contribute to the Compton continuum and the low-energy tail of the photopeak. Thus, rejecting such events should not affect significantly the photopeak efficiency, but should improve the spectral response, e.g., the peak-to-Compton ratio, for a detector fabricated from material with relaxed crystal quality requirements. Such crystals are those currently available from vendors. The use of stronger ICC correlation-function rejection criteria can improve the energy resolution of these lower-quality crystals, but at the price of a loss in photoefficiency.

  1. Detector Performance of Ammonium-Sulfide-Passivated CdZnTe and CdMnTe Materials

    SciTech Connect

    Kim, K.H.; Bolotnikov, A.E.; Camarda, G.S.; Marchini, L.; Yang, G.; Hossain, A.; Cui, Y.; Xu, L.; and James, R.B.

    2010-08-01

    Dark currents, including those in the surface and bulk, are the leading source of electronic noise in X-ray and gamma detectors, and are responsible for degrading a detector's energy resolution. The detector material itself determines the bulk leakage current; however, the surface leakage current is controllable by depositing appropriate passivation layers. In previous research, we demonstrated the effectiveness of surface passivation in CZT (CdZnTe) and CMT (CdMnTe) materials using ammonium sulfide and ammonium fluoride. In this research, we measured the effect of such passivation on the surface states of these materials, and on the performances of detectors made from them.

  2. Effect of ZnTe and CdZnTe Alloys at the Back Contact of 1-μm-Thick CdTe Thin Film Solar Cells

    NASA Astrophysics Data System (ADS)

    Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    2002-05-01

    N2-doped ZnTe was introduced onto 1-μm-thick CdTe absorbers in order to reduce the carrier recombination at the back contact of CdS/CdTe/C/Ag configuration solar cells. ZnTe films were grown by molecular beam epitaxy (MBE) on GaAs and Corning glass substrates to investigate the characteristics of the films. Epitaxial growth of ZnTe was realized on GaAs substrates and a hole concentration of 8 × 1018 cm-3 with a resistivity of 0.045 Ω \\cdotcm was achieved as a result of nitrogen doping. In contrast, polycrystalline ZnTe films were grown on Corning glass and CdTe thin films. Dark and photoconductivity of ZnTe films increased to 1.43 × 10-5 S/cm and 1.41 × 10-4 S/cm, respectively, while the Zn to Te ratio was decreased to 0.25 during MBE growth. These ZnTe films with different thicknesses were inserted into close-spaced sublimation (CSS)-grown 1-μm-thick CdTe solar cells. A conversion efficiency of 8.31% (Voc: 0.74 V, Jsc: 22.98 mA/cm2, FF: 0.49, area: 0.5 cm2) was achieved for a 0.2-μm-thick ZnTe layer with a cell configuration of CdS/CdTe/ZnTe/Cu-doped-C/Ag. Furthermore, to overcome the problem of possible recombination loss in the interface layer of CdTe and ZnTe, the intermediate ternary CdZnTe is investigated. The compositional factor in Cd1-xZnxTe:N alloy is varied and the dependence of the conductivity is evaluated. For instance, Cd0.5Zn0.5Te:N, with dark and photoconductivity of 2.13 × 10-6 and 2.9 × 10-5 S/cm, respectively, is inserted at the back contact of a 1-μm-thick CdTe solar cell. A conversion efficiency of 7.46% (Voc: 0.68 V, Jsc: 22.60 mA/cm2, FF: 0.49, area: 0.086 cm2) was achieved as the primary result for a 0.2-μm-thick Cd0.5Zn0.5Te:N layer with the cell configuration of CdS/CdTe/Cd0.5Zn0.5Te:N/Au.

  3. Internal Electric-Field-Lines Distribution in Cdznte Detectors Measured Using X-ray Mapping

    SciTech Connect

    Bolotnikov, A.; Camarda, C; Cui, Y; Hossain, A; Yang, G; Yao, H; James, R

    2009-01-01

    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 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.

  4. Charge transport in CdZnTe coplanar grid detectors examined by laser induced transient currents

    NASA Astrophysics Data System (ADS)

    Praus, P.; Kunc, J.; Belas, E.; Pekárek, J.; Grill, R.

    2016-09-01

    Laser-induced transient current technique was used for the visualization of charge transfer in the coplanar CdZnTe radiation detector including distinction to the collecting and noncollecting grids. Transient current waveforms measured at different intergrid biasing allowed us the identification of principal charge transit features and the final redistribution of collected charge between grids. We have demonstrated that while at the initial period of the charge passage through the detector bulk the current waveform shapes on the collection and non-collection electrodes are nearly the same, the intergrid biasing entails significant current deviation at the final part of the transients, where inverted current through the non-collecting grid induces markedly reduced/enhanced collected charge in the non-collecting/collecting electrode. An optimum ratio of cathode/intergrid biasing was found to be close to the ratio of detector/intergrid dimensions. Theoretical simulations demonstrating all charge-transfer characteristics were presented and proved the validity of the experimental data.

  5. Low-noise custom VLSI for CdZnTe pixel detectors

    NASA Astrophysics Data System (ADS)

    Cook, Walter R.; Burnham, Jill A.; Harrison, Fiona A.

    1998-11-01

    A custom analog VLSI chip is being developed for the readout of pixelated CdZnTe detectors in the focal plane of an astronomical hard x-ray telescope. The chip is intended for indium bump bonding to a pixel detector having pitch near 0.5 mm. A complete precision analog signal processing chain, including charge sensitive preamplifier, shaping amplifiers and peak detect and hold circuit, is provided for each pixel. Here we describe the circuitry and discus the performance of a functional prototype fabricated in a 1.2 micrometers CMOS process at Orbit Semiconductor. Dynamic performance is found to be close to SPICE model predictions over a self-triggering range extending from 1 to 50 keV. Integral non-linearity and noise while acceptable ar not as god as predicted. Power consumption is only 250 uW per pixel. Layout and design techniques are discussed which permit successful self-triggering operation at the low 1 keV threshold.

  6. CHARACTERIZATION OF PD IMPURITIES AND TWIN BOUNDARY DEFECTS IN DETECTOR GRADE CDZNTE CRYSTALS

    SciTech Connect

    Duff, M.

    2011-06-22

    Synthetic CdZnTe or ''CZT'' crystals are highly suitable for {gamma}-spectrometers operating at the room temperature. Secondary phases (SP) in CZT are known to inhibit detector performance, particularly when they are present in large numbers or dimensions. These SP may exist as voids or composites of non-cubic phase metallic Te layers with bodies of polycrystalline and amorphous CZT material and voids. Defects associated with crystal twining may also influence detector performance in CZT. Using transmission electron microscopy, we identify two types of defects that are on the nano scale. The first defect consists of 40 nm diameter metallic Pd/Te bodies on the grain boundaries of Te-rich composites. Although the nano-Pd/Te bodies around these composites may be unique to the growth source of this CZT material, noble metal impurities like these may contribute to SP formation in CZT. The second defect type consists of atom-scale grain boundary dislocations. Specifically, these involve inclined ''finite-sized'' planar defects or interfaces between layers of atoms that are associated with twins. Finite-sized twins may be responsible for the subtle but observable striations that can be seen with optical birefringence imaging and synchrotron X-ray topographic imaging.

  7. Use of high-granularity position sensing to correct response non-uniformities of CdZnTe detectors

    SciTech Connect

    Bolotnikov, A. E. Camarda, G. S.; Cui, Y.; De Geronimo, G.; Fried, J.; Hossain, A.; Mahler, G.; Maritato, M.; Marshall, M.; Roy, U.; Vernon, E.; Yang, G.; James, R. B.; Lee, K.; Petryk, M.

    2014-06-30

    CdZnTe (CZT) is a promising medium for room-temperature gamma-ray detectors. However, the low production yield of acceptable quality crystals hampers the use of CZT detectors for gamma-ray spectroscopy. Significant efforts have been directed towards improving quality of CZT crystals to make them generally available for radiation detectors. Another way to address this problem is to implement detector designs that would allow for more accurate and predictable correction of the charge loss associated with crystal defects. In this work, we demonstrate that high-granularity position-sensitive detectors can significantly improve the performance of CZT detectors fabricated from CZT crystals with wider acceptance boundaries, leading to an increase of their availability and expected decrease in cost.

  8. Influence of the thickness of a crystal on the electrical characteristics of Cd(Zn)Te detectors

    SciTech Connect

    Sklyarchuk, V.; Fochuk, p.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O. F.; Bolotnikov, A. E.; James, R. B.

    2015-08-01

    We studied the electrical characteristics of Cd(Zn)Te detectors with rectifying contacts and varying thicknesses, and established that their geometrical dimensions affect the measured electrical properties. We found that the maximum value of the operating-bias voltage and the electric field in the detector for acceptable values of the dark current can be achieved when the crystal has an optimum thickness. This finding is due to the combined effect of generation-recombination in the space-charge region and space-charge limited currents (SCLC).

  9. Development of CDZNTE Detectors for Low-Energy Gamma-Ray Astronomy

    NASA Technical Reports Server (NTRS)

    Gehrels, N.

    1999-01-01

    Under this grant the UC Berkeley PI, K. Hurley, joined a Goddard-led effort to develop large area, multi-pixel Cadmium-Zinc-Telluride (CdZnTe, or CZT) detectors for gamma-ray astronomy. His task was to advise the project of new developments in the area of cosmic gamma-ray bursts, in order to focus the detector development effort on the construction of an instrument which could be deployed on a spacecraft to localize and measure the energy spectra of bursts with good angular and energy resolution, respectively. UC Berkeley had no hardware role in this proposal. The result of this effort was the production, at Goddard, of five CZT prototype modules. A proposal was written for SWIFT, a MIDEX mission to study cosmic gamma-ray bursts. One experiment aboard SWIFT is the Burst Arcminute Telescope (BAT), which consists of a 5200 sq cm hard X-ray detector and a coded mask. The detector comprises 256 CZT modules, each containing 128 4 x 4 x 2 mm CZT detectors. Each detector is read out using an ASIC. The angular resolution achieved with this mask/array combination is 22 arcminutes, and a strong gamma-ray burst can be localized to an accuracy of 4 arcminutes in under 10 seconds. The energy resolution is typically 5 keV FWHM at 60 keV, and the energy range is 10 - 150 keV. The BAT views 2 steradians, and its sensitivity is such that the instrument can detect 350 gamma-ray burst/year, localizing 320 of them to better than 4 arcminute accuracy. The BAT concept therefore met the science goals for gamma-ray bursts. The UCB effort in the SWIFT proposal included the scientific objectives for gamma-ray bursts, and the assembly of a team of optical and radio observers who would use the BAT data to perform rapid multi-wavelength searches for the counterparts to bursts. This proposal was submitted to NASA and peer-reviewed. In January 1999 it was one of five such proposals selected for a Phase A study. This study was completed in June, and SWIFT was formally presented to NASA in

  10. Characteristics of a Frisch collar grid CdZnTe radiation detector grown by low-pressure Bridgman method

    NASA Astrophysics Data System (ADS)

    Jeong, Manhee; Jo, Woo Jin; Kim, Han Soo; Ha, Jang Ho

    2015-06-01

    A single-polarity charge-sensing method was studied by using a CdZnTe Frisch collar grid detector grown by using a low-pressure Bridgeman furnace at the Korea Atomic Energy Research Institute (KAERI). The Frisch collar grid CdZnTe detector has an active volume of 5 × 5 × 10 mm3, and was fabricated from a single crystal, Teflon tape and copper tape used as a Frisch collar grid. A room-temperature energy resolution of 6% full width at half maximum (FWHM) was obtained for the 662keV peak of Cs-137 without any additional electrical corrections. The detector's fabrication process is described, and its characteristics are discussed. Finally, the charge transport properties and gamma-ray energy resolution of the fabricated Frisch collar grid detector are compared with those of two other Frisch collar detectors grown by using different crystal growth methods and purchased from eV-products and Redlen technology.

  11. CdZnTe arrays for nuclear medicine imaging

    SciTech Connect

    Barber, H.B.

    1996-12-31

    In nuclear medicine, a gamma-ray-emitting radiotracer is injected into the body, and the resulting biodistribution is imaged using a gamma camera. Current gamma cameras use a design developed by Anger. An Anger camera makes use of a slab of scintillation detector that is viewed by an array of photomultiplier tubes and uses an analog position estimation technique to determine the position of the gamma ray`s interaction. The image-forming optics is usually a multi-bore collimator made of lead. Such cameras are characterized by poor, system spatial resolution ({approximately}1 cm) due to poor detector resolution ({approximately}0.4 cm) and poor collimator performance. Arrays of semiconductor detectors are an attractive alternative to scintillators for use in gamma cameras. Semiconductor detectors have excellent energy resolution. High spatial resolution is also possible because large semiconductor detector arrays with small pixel sizes can be produced using photolithography techniques. A new crystal growth technique (high-pressure vertical Bridgman) allows production of detector grade CdTe and CdZnTe in multikilogram ingots. Although the cost of CdZnTe detectors has come down substantially in the last few years, in part because of economies of scale, costs are still more than an order of magnitude higher than those required for a commercial camera ($20--$50/gram). High detector costs are perhaps the major stumbling block to developing a semiconductor gamma camera. The photolithography techniques required to make large CdZnTe arrays have already been demonstrated. This paper discusses the recent developments made in CdZnTe detectors.

  12. An effect of the networks of the subgrain boundaries on spectral responses of thick CdZnTe detectors

    SciTech Connect

    Bolotnikov, A.; Butcher, J.; Camarda, G.; Cui, Y.; Egarievwe, S.; Fochuk, P.; Gul,R.; Hamade, M.; Hossain, A.; Kim, K.; Kopach,O.; Petryk, M.; Raghothamachar, B.; Yang, G.; and James, R.B.

    2011-08-12

    CdZnTe (CZT) crystals used for nuclear-radiation detectors often contain high concentrations of subgrain boundaries and networks of poligonized dislocations that can significantly degrade the performance of semiconductor devices. These defects exist in all commercial CZT materials, regardless of their growth techniques and their vendor. We describe our new results from examining such detectors using IR transmission microscopy and white X-ray beam diffraction topography. We emphasize the roles on the devices performances of networks of subgrain boundaries with low dislocation densities, such as poligonized dislocations and mosaic structures. Specifically, we evaluated their effects on the gamma-ray responses of thick, >10 mm, CZT detectors. Our findings set the lower limit on the energy resolution of CZT detectors containing dense networks of subgrain boundaries, and walls of dislocations.

  13. Electronics System for the GammaTracker Handheld CdZnTe Detector

    SciTech Connect

    Myjak, Mitchell J.; Morris, Scott J.; Slaugh, Ryan W.; McCann, Jason M.; Kirihara, Leslie J.; Rohrer, John S.; Burghard, Brion J.; Seifert, Carolyn E.

    2007-12-31

    We are currently developing a handheld radioisotope identifier containing eighteen position-sensitive CdZnTe crystals. In addition to isotope identification, the device performs basic Compton imaging to determine the location of suspected sources. This paper gives an overview of the electronics system we have designed for this instrument. We use specialized application-specific integrated circuits to preprocess the outputs of each CdZnTe crystal. A low-power microprocessor running Windows CE drives the user interface and implements the isotope identification and directionality computations. Finally, we use a field-programmable gate array to perform the computationally intensive imaging tasks in real time.

  14. The use of Schottky CdTe detectors for high-energy astronomy: application to the detection plane of the instrument SVOM/ECLAIRs

    NASA Astrophysics Data System (ADS)

    Nasser, G.; Godet, O.; Atteia, J.-L.; Amoros, C.; Barret, D.; Bordon, S.; Cordier, B.; Gevin, O.; Gonzalez, F.; Houret, B.; Lacombe, K.; Mandrou, P.; Marty, W.; Mercier, K.; Pons, R.; Rambaud, D.; Ramon, P.; Rouaix, G.; Waegebaert, V.

    2014-07-01

    Ohmic CdZnTe and CdTe detectors have been successfully used in high-energy missions such as IBIS on-board INTEGRAL and the Swift-BAT in the past two decades. Such detectors provide very good quantum efficiency in the hard X-ray band. For the future generation of hard X-ray coded mask detectors, a higher sensitivity will be required. A way to achieve this is to increase the effective area of the pixilated detection plane, to change the mask pattern and/or the properties of the semi-conductors paving the detection plane. For the future Chinese-French Gamma-ray burst mission SVOM, the GRB trigger camera ECLAIRs will make use of a new type of high-energy detectors, the Schottky CdTe detectors. Such detectors, when reversely biased, are known to present very low leakage current, resulting in lower values of the low-energy threshold (down to 4 keV or less) than for previous missions (i.e. > 10 keV for the Swift-BAT and INTEGRAL/IBIS). Such low values will enable ECLAIRs with a moderate geometrical area of 1024 cm2 and a low-energy threshold of 4 keV to be more sensitive to high-redshift GRBs (emitting mainly in X-rays) than the Swift-BAT with a higher effective area and low-energy threshold. However, the spectral performance of such detectors are known to degrade over time, once polarized, due to the polarization effect that strongly depends on the temperature and the bias voltage applied to the detectors. In this paper, we present an intensive study of the properties of Schottky CdTe detectors as used on SVOM/ECLAIRs such as I-V characteristics, polarization effect, activation energy and low temperature annealing effects. We discuss the implications of these measurements on the use of this type of detectors in future high-energy instruments.

  15. SEMICONDUCTOR DEVICES Parallel readout of two-element CdZnTe detectors with real-time digital signal processing

    NASA Astrophysics Data System (ADS)

    Zhubin, Shi; Linjun, Wang; Kaifeng, Qin; Jiahua, Min; Jijun, Zhang; Xiaoyan, Liang; Jian, Huang; Ke, Tang; Yiben, Xia

    2010-12-01

    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 especially in energy resolution. The energy resolution by the means of digital electronics can be improved by about 26.67%, compared to that only with analog electronics, while their detection efficiency is almost the same. The cause for this difference is also discussed.

  16. Investigation of Charge Transport Properties of CdZnTe Detectors with Synchrotron X-ray Radiation

    SciTech Connect

    Yang,G.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Hossain, A.; James, R.B.

    2008-10-19

    Various internal defects, such as Te inclusions, twin boundaries, dislocation, etc., are prevalent in as-grown CdZnTe (CZT) crystals, which affect the charge transport properties of CZT crystals and, therefore, worsen the performance of CZT detectors. In order to develop high quality CZT detectors, it is imperative to clarify the effects of internal defects on the charge transport properties of CZT. Simple flood illumination with nuclear radiation source cannot reveal the nature of highly localized defects in CZT. Therefore, at Brookhaven's National Synchrotron Light Source (NSLS), we have developed a unique testing system for micro-scale defect investigation of CZT, which employs an X-ray beam collimated with the spatial resolution as small as 3 x 3 {micro}m{sup 2}, a microscopic size comparable to the scale of common defects in CZT. This powerful tool enables us to investigate the effect of internal defects on charge transport properties of CZT in detail.

  17. Novel ZnO:Al contacts to CdZnTe for X- and gamma-ray detectors.

    PubMed

    Roy, U N; Mundle, R M; Camarda, G S; Cui, Y; Gul, R; Hossain, A; Yang, G; Pradhan, A K; James, R B

    2016-01-01

    CdZnTe (CZT) has made a significant impact as a material for room-temperature nuclear-radiation detectors due to its potential impact in applications related to nonproliferation, homeland security, medical imaging, and gamma-ray telescopes. In all such applications, common metals, such as gold, platinum and indium, have been used as electrodes for fabricating the detectors. Because of the large mismatch in the thermal-expansion coefficient between the metal contacts and CZT, the contacts can undergo stress and mechanical degradation, which is the main cause for device instability over the long term. Here, we report for the first time on our use of Al-doped ZnO as the preferred electrode for such detectors. The material was selected because of its better contact properties compared to those of the metals commonly used today. Comparisons were conducted for the detector properties using different contacts, and improvements in the performances of ZnO:Al-coated detectors are described in this paper. These studies show that Al:ZnO contacts to CZT radiation detectors offer the potential of becoming a transformative replacement for the common metallic contacts due to the dramatic improvements in the performance of detectors and improved long-term stability. PMID:27216387

  18. Novel ZnO:Al contacts to CdZnTe for X- and gamma-ray detectors

    PubMed Central

    Roy, U. N.; Mundle, R. M.; Camarda, G. S.; Cui, Y.; Gul, R.; Hossain, A.; Yang, G.; Pradhan, A. K.; James, R. B.

    2016-01-01

    CdZnTe (CZT) has made a significant impact as a material for room-temperature nuclear-radiation detectors due to its potential impact in applications related to nonproliferation, homeland security, medical imaging, and gamma-ray telescopes. In all such applications, common metals, such as gold, platinum and indium, have been used as electrodes for fabricating the detectors. Because of the large mismatch in the thermal-expansion coefficient between the metal contacts and CZT, the contacts can undergo stress and mechanical degradation, which is the main cause for device instability over the long term. Here, we report for the first time on our use of Al-doped ZnO as the preferred electrode for such detectors. The material was selected because of its better contact properties compared to those of the metals commonly used today. Comparisons were conducted for the detector properties using different contacts, and improvements in the performances of ZnO:Al-coated detectors are described in this paper. These studies show that Al:ZnO contacts to CZT radiation detectors offer the potential of becoming a transformative replacement for the common metallic contacts due to the dramatic improvements in the performance of detectors and improved long-term stability. PMID:27216387

  19. Novel ZnO:Al contacts to CdZnTe for X- and gamma-ray detectors

    NASA Astrophysics Data System (ADS)

    Roy, U. N.; Mundle, R. M.; Camarda, G. S.; Cui, Y.; Gul, R.; Hossain, A.; Yang, G.; Pradhan, A. K.; James, R. B.

    2016-05-01

    CdZnTe (CZT) has made a significant impact as a material for room-temperature nuclear-radiation detectors due to its potential impact in applications related to nonproliferation, homeland security, medical imaging, and gamma-ray telescopes. In all such applications, common metals, such as gold, platinum and indium, have been used as electrodes for fabricating the detectors. Because of the large mismatch in the thermal-expansion coefficient between the metal contacts and CZT, the contacts can undergo stress and mechanical degradation, which is the main cause for device instability over the long term. Here, we report for the first time on our use of Al-doped ZnO as the preferred electrode for such detectors. The material was selected because of its better contact properties compared to those of the metals commonly used today. Comparisons were conducted for the detector properties using different contacts, and improvements in the performances of ZnO:Al-coated detectors are described in this paper. These studies show that Al:ZnO contacts to CZT radiation detectors offer the potential of becoming a transformative replacement for the common metallic contacts due to the dramatic improvements in the performance of detectors and improved long-term stability.

  20. True coincidence-summing corrections for the coincident gamma-rays measured with coplanar grid CdZnTe detectors.

    PubMed

    Yücel, H; Solmaz, A N; Köse, E; Bor, D

    2010-06-01

    In this study, true coincidence-summing (TCS) correction factors have been measured for the sources (22)Na, (60)Co, (133)Ba and (152)Eu by use of three large volume coplanar grid CdZnTe (acronym: CZT) detectors. In case of a close-in detection geometry, two different TCS calculation algorithms were used to compute the required TCS correction factors. Both of the algorithms are based on the measured total-to-peak (TTP) ratio and full-energy peak (FEP) efficiency values that were obtained using almost "single" energy and coincidence-free nuclides. The results for TCS correction factors obtained by two different algorithms were agreeable to each other. The obtained TCS factors were ranged from about 7% to 30.5% in a 2250 mm(3) CZT detector when a close counting geometry was used. For other two detectors with a volume of 1000 and 1687.5mm(3), the resulted TCS correction factors were relatively smaller and varied between about 0.1% and 20% at the close counting geometry condition. Therefore, the results indicate that there is a need for the estimation of TCS corrections in CZT detectors, especially when their crystal volumes are greater than 1cm(3) and these detectors are used in the case of a close-in detection geometry. PMID:20167503

  1. Effectiveness of electrostatic shielding and electronic subtraction to correct for the hole trapping in CdZnTe semiconductor detectors

    NASA Astrophysics Data System (ADS)

    Bolotnikov, A. E.; Camarda, G. S.; Hossain, A.; Cui, Y.; James, R. B.

    2007-04-01

    CdZnTe (CZT) is a very promising material for nuclear-radiation detectors. CZT detectors operate at ambient temperatures and offer high detection efficiency and excellent energy resolution, placing them ahead of high-purity Ge for those applications where cryogenic cooling is problematic. The progress achieved in CZT detectors over the past decade is founded on the developments of robust detector designs and readout electronics, both of which helped to overcome the effects of carrier trapping. Because the holes have low mobility, only electrons can be used to generate signals in thick CZT detectors, so one must account for the variation of the output signal versus the locations of the interaction points. To obtain high spectral resolution, the detector's design should provide a means to eliminate this dependence throughout the entire volume of the device. In reality, the sensitive volume of any ionization detector invariably has two regions. In the first, adjacent to the collecting electrode, the amplitude of the output signal rapidly increases almost to its maximum as the interaction point is located farther from the anode; in the rest of the volume, the output signal remains nearly constant. Thus, the quality of CZT detector designs can be characterized based on the magnitude of the signals variations in the drift region and the ratio between the volumes of the drift and induction regions. The former determines the "geometrical" width of the photopeak, i.e., the line width that affects the total energy resolution and is attributed to the device's geometry when all other factors are neglected. The latter determines the photopeak efficiency and the area under the continuum in the pulse-height spectra. In this work, we describe our findings from systematizing different designs of CZT detectors and evaluating their performance based on these two criteria.

  2. EFFECTIVENESS OF ELECTROSTATIC SHIELDING AND ELECTRONIC SUBTRACTION TO CORRECT FOR THE HOLE TRAPPING IN CDZNTE SEMICONDUCTOR DETECTORS.

    SciTech Connect

    BOLOTNIKOV,A.E.; CAMARDA, G.S.; HOSSAIN, A.; CUI, Y.; JAMES, R.B.

    2007-08-26

    CdZnTe (CZT) is a very promising material for nuclear-radiation detectors. CZT detectors operate at ambient temperatures and offer high detection efficiency and excellent energy resolution, placing them ahead of high-purity Ge for those applications where cryogenic cooling is problematic. The progress achieved in CZT detectors over the past decade is founded on the developments of robust detector designs and readout electronics, both of which helped to overcome the effects of carrier trapping. Because the holes have low mobility, only electrons can be used to generate signals in thick CZT detectors, so one must account for the variation of the output signal versus the locations of the interaction points. To obtain high spectral resolution, the detector's design should provide a means to eliminate this dependence throughout the entire volume of the device. In reality, the sensitive volume of any ionization detector invariably has two regions. In the first, adjacent to the collecting electrode, the amplitude of the output signal rapidly increases almost to its maximum as the interaction point is located farther from the anode; in the rest of the volume, the output signal remains nearly constant. Thus, the quality of CZT detector designs can be characterized based on the magnitude of the signals variations in the drift region and the ratio between the volumes of the driR and induction regions. The former determines the ''geometrical'' width of the photopeak i.e., the line width that affects the total energy resolution and is attributed to the device's geometry when all other factors are neglected. The latter determines the photopeak efficiency and the area under the continuum in the pulse-height spectra. In this work, we describe our findings from systematizing different designs of CZT detectors and evaluating their performance based on these two criteria.

  3. Synchrotron x-ray photoconductor detector arrays made on MBE grown CdTe

    SciTech Connect

    Yoo, S.S.; Montano, P.A. |; Rodricks, B.; Sivananthan, S.; Faurie, J.P.

    1996-08-01

    We have been fabricating x-ray photoconductor linear array detectors using molecular beam epitaxially (MBE) grown (111)B undoped CdTe layers on (100) Si substrates. A novel technique was developed to remove the Si and to mount the fragile MBE grown CdTe layers onto insulating ceramic substrates. 256 channel linear photoconductor array devices were fabricated on the resulting CdTe layers. The resistivity of MBE (111)B CdTe was high (> 10{sup 8} {Omega}cm) enough to utilize the material for low energy (8 to 25 keV) x-ray detectors. The stability of the detectors are satisfactory, and they were tested at room temperature routinely for over a year. The performance of the photoconductor was greatly improved when the detector was cooled to 230K. Due to its reduced dark current at low temperatures, the dynamic range of the detector response increased to nearly four decades at 230K. 29 refs., 8 figs.

  4. Design and performances of a low-noise and radiation-hardened readout ASIC for CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Bo, Gan; Tingcun, Wei; Wu, Gao; Yongcai, Hu

    2016-06-01

    In this paper, we present the design and performances of a low-noise and radiation-hardened front-end readout application specific integrated circuit (ASIC) dedicated to CdZnTe detectors for a hard X-ray imager in space applications. The readout channel is comprised of a charge sensitive amplifier, a CR-RC shaping amplifier, an analog output buffer, a fast shaper, and a discriminator. An 8-channel prototype ASIC is designed and fabricated in TSMC 0.35-μm mixed-signal CMOS technology, the die size of the prototype chip is 2.2 × 2.2 mm2. The input energy range is from 5 to 350 keV. For this 8-channel prototype ASIC, the measured electrical characteristics are as follows: the overall gain of the readout channel is 210 V/pC, the linearity error is less than 2%, the crosstalk is less than 0.36%, The equivalent noise charge of a typical channel is 52.9 e- at zero farad plus 8.2 e- per picofarad, and the power consumption is less than 2.4 mW/channel. Through the measurement together with a CdZnTe detector, the energy resolution is 5.9% at the 59.5-keV line under the irradiation of the radioactive source 241Am. The radiation effect experiments show that the proposed ASIC can resist the total ionization dose (TID) irradiation of higher than 200 krad(Si). Project supported by the National Key Scientific Instrument and Equipment Development Project (No. 2011YQ040082), the National Natural Science Foundation of China (Nos. 11475136, 11575144, 61176094), and the Shaanxi Natural Science Foundation of China (No. 2015JM1016).

  5. Design and performances of a low-noise and radiation-hardened readout ASIC for CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Bo, Gan; Tingcun, Wei; Wu, Gao; Yongcai, Hu

    2016-06-01

    In this paper, we present the design and performances of a low-noise and radiation-hardened front-end readout application specific integrated circuit (ASIC) dedicated to CdZnTe detectors for a hard X-ray imager in space applications. The readout channel is comprised of a charge sensitive amplifier, a CR-RC shaping amplifier, an analog output buffer, a fast shaper, and a discriminator. An 8-channel prototype ASIC is designed and fabricated in TSMC 0.35-μm mixed-signal CMOS technology, the die size of the prototype chip is 2.2 × 2.2 mm2. The input energy range is from 5 to 350 keV. For this 8-channel prototype ASIC, the measured electrical characteristics are as follows: the overall gain of the readout channel is 210 V/pC, the linearity error is less than 2%, the crosstalk is less than 0.36%, The equivalent noise charge of a typical channel is 52.9 e‑ at zero farad plus 8.2 e‑ per picofarad, and the power consumption is less than 2.4 mW/channel. Through the measurement together with a CdZnTe detector, the energy resolution is 5.9% at the 59.5-keV line under the irradiation of the radioactive source 241Am. The radiation effect experiments show that the proposed ASIC can resist the total ionization dose (TID) irradiation of higher than 200 krad(Si). Project supported by the National Key Scientific Instrument and Equipment Development Project (No. 2011YQ040082), the National Natural Science Foundation of China (Nos. 11475136, 11575144, 61176094), and the Shaanxi Natural Science Foundation of China (No. 2015JM1016).

  6. Study on the bias-dependent effects of proton-induced damage in CdZnTe radiation detectors using ion beam induced charge microscopy.

    PubMed

    Gu, Yaxu; Jie, Wanqi; Rong, Caicai; Xu, Lingyan; Xu, Yadong; Lv, Haoyan; Shen, Hao; Du, Guanghua; Guo, Na; Guo, Rongrong; Zha, Gangqiang; Wang, Tao; Xi, Shouzhi

    2016-09-01

    The influence of damage induced by 2MeV protons on CdZnTe radiation detectors is investigated using ion beam induced charge (IBIC) microscopy. Charge collection efficiency (CCE) in irradiated region is found to be degraded above a fluence of 3.3×10(11)p/cm(2) and the energy spectrum is severely deteriorated with increasing fluence. Moreover, CCE maps obtained under the applied biases from 50V to 400V suggests that local radiation damage results in significant degradation of CCE uniformity, especially under low bias, i. e., 50V and 100V. The CCE nonuniformity induced by local radiation damage, however, can be greatly improved by increasing the detector applied bias. This bias-dependent effect of 2MeV proton-induced radiation damage in CdZnTe detectors is attributed to the interaction of electron cloud and radiation-induced displacement defects. PMID:27399802

  7. Simulation of active-edge pixelated CdTe radiation detectors

    NASA Astrophysics Data System (ADS)

    Duarte, D. D.; Lipp, J. D.; Schneider, A.; Seller, P.; Veale, M. C.; Wilson, M. D.; Baker, M. A.; Sellin, P. J.

    2016-01-01

    The edge surfaces of single crystal CdTe play an important role in the electronic properties and performance of this material as an X-ray and γ-ray radiation detector. Edge effects have previously been reported to reduce the spectroscopic performance of the edge pixels in pixelated CdTe radiation detectors without guard bands. A novel Technology Computer Aided Design (TCAD) model based on experimental data has been developed to investigate these effects. The results presented in this paper show how localized low resistivity surfaces modify the internal electric field of CdTe creating potential wells. These result in a reduction of charge collection efficiency of the edge pixels, which compares well with experimental data.

  8. High-Efficiency CdZnTe Position-Sensitive VFG Gamma-Ray Detectors for Safeguards Applications

    SciTech Connect

    Bolotnikov, Aleksey E.; James, Ralph B.; Cui, Y.; De Geronimo, G.; Vernon, E.; Camarda, G. S.; Hossain, A.; Yang, G.; Indusi, J.; Boyer, Brian

    2015-09-30

    The goal of this project is to incorporate a Cadmium-Zinc-Telluride (CdZnTe or CZT) detector (with 1% or better resolution) into a bench-top prototype for isotope identification and related safeguards applications. The bench-top system is based on a 2x2 array of 6x6x20 mm3 position-sensitive virtual Frisch-grid (VFG) CZT detectors. The key features of the array are that it allows for the use of average-grade CZT material with a moderate content of defects, and yet it provides high-energy resolution, 1% FWHM at 662 keV, large effective area, and low-power consumption. The development of this type of 3D detector and new instruments incorporating them is motivated by the high cost and low availability of large, > 1 cm3, CZT crystals suitable for making multi-pixel detectors with acceptable energy resolution and efficiency.

  9. Experimental study of {sup 113}Cd {beta} decay using CdZnTe detectors

    SciTech Connect

    Goessling, C.; Kiel, H.; Muenstermann, D.; Oehl, S.; Junker, M.; Zuber, K.

    2005-12-15

    A search for the fourfold forbidden {beta} decay of {sup 113}Cd has been performed with CdZnTe semiconductors. With 0.86 kg {center_dot} d of statistics a half-life for the decay of T{sub 1/2}=[8.2{+-}0.2(stat.){sub -1.0}{sup +0.2}(sys.)]x10{sup 15} yr has been obtained. This is in good agreement with published values. A comparison of the spectral shape with the one given on the Table of Isotopes Web page shows a severe deviation.

  10. PERFORMANCE STUDIES OF CDZNTE DETECTOR BY USING A PULSE SHAPE ANALYSIS.

    SciTech Connect

    BOLOTNIKOV, A.

    2005-07-31

    Pulse shape analysis is proved to be a powerful tool to characterize the performance of CdZnTe devices and understand their operating principles. It allows one to investigate the device configurations, electron transport properties, effects governing charge collection, electric-field distributions, signal charge formation, etc. This work describes an application of different techniques based on the pulse shape measurements to characterize pixel, coplanar-grid, and virtual Frisch-grid devices and understand the electronic properties of CZT material provided by different vendors. We report new results that may explain the performance limits of these devices.

  11. First test results from a high-resolution CdZnTe pixel detector with VLSI readout

    NASA Astrophysics Data System (ADS)

    Cook, Walter R.; Boggs, Steven E.; Bolotnikov, Aleksey E.; Burnham, Jill A.; Harrison, Fiona A.; Kecman, Branislav; Matthews, Brian; Schindler, Steven M.; Fitzsimmons, Michael

    1999-10-01

    We are developing a CdZnTe pixel detector with a custom low- noise analog VLSI readout for use in the High-Energy Focusing Telescope balloon experiment, as well as for future space astronomy applications. The goal of the program is to achieve good energy resolution (< 1 keV FWHM at 60 keV) and low threshold in a sensor with approximately 500 micrometers pixels. We have fabricated several prototype detector assemblies with 2 mm thick, 680 by 650 micrometers pitch CdZnTe pixel sensors indium bump bonded a VLSI readout chip developed at Caltech. Each readout circuit in the 8 X 8 prototype is matched to the detector pixel size, and contains a preamplifier, shaping amplifiers, and a peak stretcher/discriminator. In the first 8 X 8 prototype, we have demonstrated the low-noise preamplifier by routing the output signals off-chip for shaping and pulse-height analysis. Pulse height spectra obtained using a 241Am source, collimated to illuminate a single pixel, show excellent energy resolution of 1.1 keV FWHM for the 60 keV line at room temperature. Line profiles are approximately Gaussian and dominated by electronic noise, however a small low energy tail is evident for the 60 keV line. We obtained slightly improved resolution of 0.9 keV FWHM at 60 keV by cooling the detector to 5 degree(s)C, near the expected balloon- flight operating temperature. Pulse height spectra obtained with the collimated source positioned between pixels show the effect of signal sharing for events occurring near the boundary. We are able to model the observed spectra using a Monte-Carlo simulation that includes the effects of photon interaction, charge transport and diffusion, pixel and collimator geometry, and electronic noise. By using the model to simulate the detector response to uncollimated radiation (including the effect of finite trigger threshold for reconstruction of the total energy of multi-pixel events), we find the energy resolution to be degraded by only 10% for full

  12. Effects of Chemomechanical Polishing on CdZnTe X-ray and Gamma-Ray Detectors

    NASA Astrophysics Data System (ADS)

    Egarievwe, Stephen U.; Hossain, Anwar; Okwechime, Ifechukwude O.; Gul, Rubi; James, Ralph B.

    2015-09-01

    Mechanically polishing cadmium zinc telluride (CdZnTe) wafers for x-ray and gamma-ray detectors often is inadequate in removing surface defects caused by cutting them from the ingots. Fabrication-induced defects, such as surface roughness, dangling bonds, and nonstoichiometric surfaces, often are reduced through polishing and etching the surface. In our earlier studies of mechanical polishing with alumina powder, etching with hydrogen bromide in hydrogen peroxide solution, and chemomechanical polishing with bromine-methanol-ethylene glycol solution, we found that the chemomechanical polishing process produced the least surface leakage current. In this research, we focused on using two chemicals to chemomechanically polish CdZnTe wafers after mechanical polishing, viz. bromine-methanol-ethylene glycol (BME) solution, and hydrogen bromide (HBr) in a hydrogen peroxide and ethylene-glycol solution. We used x-ray photoelectron spectroscopy (XPS), current-voltage ( I- V) measurements, and Am-241 spectral response measurements to characterize and compare the effects of each solution. The results show that the HBr-based solution produced lower leakage current than the BME solution. Results from using the same chemomechanical polishing solution on two samples confirmed that the surface treatment affects the measured bulk current (a combination of bulk and surface currents). XPS results indicate that the tellurium oxide to tellurium peak ratios for the mechanical polishing process were reduced significantly by chemomechanical polishing using the BME solution (78.9% for Te 3 d 5/2O2 and 76.7% for Te 3 d 3/2O2) compared with the HBr-based solution (27.6% for Te 3 d 5/2O2 and 35.8% for Te 3 d 3/2O2). Spectral response measurements showed that the 59.5-keV peak of Am-241 remained under the same channel number for all three CdZnTe samples. While the BME-based solution gave a better performance of 7.15% full-width at half-maximum (FWHM) compared with 7.59% FWHM for the HBr

  13. Effects of chemo-mechanical polishing on CdZnTe X-ray and gamma-ray detectors

    SciTech Connect

    Egarievwe, Stephen E.; Hossain, Anwar; Okwechime, Ifechukwude O.; Gul, Rubi; James, Ralph B.

    2015-06-23

    Here, mechanically polishing cadmium zinc telluride (CdZnTe) wafers for x-ray and gamma-ray detectors often is inadequate in removing surface defects caused by cutting them from the ingots. Fabrication-induced defects, such as surface roughness, dangling bonds, and nonstoichiometric surfaces, often are reduced through polishing and etching the surface. In our earlier studies of mechanical polishing with alumina powder, etching with hydrogen bromide in hydrogen peroxide solution, and chemomechanical polishing with bromine–methanol–ethylene glycol solution, we found that the chemomechanical polishing process produced the least surface leakage current. In this research, we focused on using two chemicals to chemomechanically polish CdZnTe wafers after mechanical polishing, viz. bromine–methanol–ethylene glycol (BME) solution, and hydrogen bromide (HBr) in a hydrogen peroxide and ethylene–glycol solution. We used x-ray photoelectron spectroscopy (XPS), current–voltage (I–V) measurements, and Am-241 spectral response measurements to characterize and compare the effects of each solution. The results show that the HBr-based solution produced lower leakage current than the BME solution. Results from using the same chemomechanical polishing solution on two samples confirmed that the surface treatment affects the measured bulk current (a combination of bulk and surface currents). XPS results indicate that the tellurium oxide to tellurium peak ratios for the mechanical polishing process were reduced significantly by chemomechanical polishing using the BME solution (78.9% for Te 3d5/2O2 and 76.7% for Te 3d3/2O2) compared with the HBr-based solution (27.6% for Te 3d5/2O2 and 35.8% for Te 3d3/2O2). Spectral response measurements showed that the 59.5-keV peak of Am-241 remained under the same channel number for all three CdZnTe samples. While the BME-based solution gave a better

  14. Effects of chemo-mechanical polishing on CdZnTe X-ray and gamma-ray detectors

    DOE PAGES

    Egarievwe, Stephen E.; Hossain, Anwar; Okwechime, Ifechukwude O.; Gul, Rubi; James, Ralph B.

    2015-06-23

    Here, mechanically polishing cadmium zinc telluride (CdZnTe) wafers for x-ray and gamma-ray detectors often is inadequate in removing surface defects caused by cutting them from the ingots. Fabrication-induced defects, such as surface roughness, dangling bonds, and nonstoichiometric surfaces, often are reduced through polishing and etching the surface. In our earlier studies of mechanical polishing with alumina powder, etching with hydrogen bromide in hydrogen peroxide solution, and chemomechanical polishing with bromine–methanol–ethylene glycol solution, we found that the chemomechanical polishing process produced the least surface leakage current. In this research, we focused on using two chemicals to chemomechanically polish CdZnTe wafers aftermore » mechanical polishing, viz. bromine–methanol–ethylene glycol (BME) solution, and hydrogen bromide (HBr) in a hydrogen peroxide and ethylene–glycol solution. We used x-ray photoelectron spectroscopy (XPS), current–voltage (I–V) measurements, and Am-241 spectral response measurements to characterize and compare the effects of each solution. The results show that the HBr-based solution produced lower leakage current than the BME solution. Results from using the same chemomechanical polishing solution on two samples confirmed that the surface treatment affects the measured bulk current (a combination of bulk and surface currents). XPS results indicate that the tellurium oxide to tellurium peak ratios for the mechanical polishing process were reduced significantly by chemomechanical polishing using the BME solution (78.9% for Te 3d5/2O2 and 76.7% for Te 3d3/2O2) compared with the HBr-based solution (27.6% for Te 3d5/2O2 and 35.8% for Te 3d3/2O2). Spectral response measurements showed that the 59.5-keV peak of Am-241 remained under the same channel number for all three CdZnTe samples. While the BME-based solution gave a better performance of 7.15% full-width at half-maximum (FWHM) compared with 7.59% FWHM

  15. Al-doped ZnO contact to CdZnTe for x- and gamma-ray detector applications

    NASA Astrophysics Data System (ADS)

    Roy, U. N.; Camarda, G. S.; Cui, Y.; Gul, R.; Hossain, A.; Yang, G.; Mundle, R. M.; Pradhan, A. K.; James, R. B.

    2016-06-01

    The poor adhesion of common metals to CdZnTe (CZT)/CdTe surfaces has been a long-standing challenge for radiation detector applications. In this present work, we explored the use of an alternative electrode, viz., Al-doped ZnO (AZO) as a replacement to common metallic contacts. ZnO offers several advantages over the latter, such as having a higher hardness, a close match of the coefficients of thermal expansion for CZT and ZnO, and better adhesion to the surface of CZT due to the contact layer being an oxide. The AZO/CZT contact was investigated via high spatial-resolution X-ray response mapping for a planar detector at the micron level. The durability of the device was investigated by acquiring I-V measurements over an 18-month period, and good long-term stability was observed. We have demonstrated that the AZO/CZT/AZO virtual-Frisch-grid device performs fairly well, with comparable or better characteristics than that for the same detector fabricated with gold contacts.

  16. Structural and Electronic Properties of Gold Contacts on CdZnTe with Different Surface Finishes for Radiation Detector Applications

    NASA Astrophysics Data System (ADS)

    Tari, S.; Aqariden, F.; Chang, Y.; Ciani, A.; Grein, C.; Li, Jin; Kioussis, N.

    2014-08-01

    State-of-the-art room-temperature, high-resolution x-ray and gamma-ray semiconductor detectors can be fabricated from CdZnTe (CZT) crystals. The structural and electronic properties of the CZT surface, especially the contact interfaces, can have a substantial effect on radiation detector performance, for example leakage current, signal-to-noise ratio, and energy resolution, especially for soft x-rays and large pixilated arrays. Atomically smooth and defect-free surfaces are desirable for high-performance CZT-based detectors; chemo-mechanical polishing (CMP) is typically performed to produce such surfaces. The electrical behavior of the metal/CZT interface varies substantially with surface preparation before contact deposition, and with choice of metal and deposition technique. We report a systematic study of the structural and electronic properties of gold (Au) contacts on CZT prepared with different surface finishes. We observed subsurface damage under Au contacts on CMP-finished CZT and abrupt interfaces for Au on chemically-polished (CP) CZT. Schottky barrier formation was observed for Au contacts, irrespective of surface finish, and less charge trapping and low surface resistance were observed for CP-finished surfaces. Pre-deposition surface treatment produced interfaces free from oxide layers.

  17. CdTe X-ray detectors under strong optical irradiation

    SciTech Connect

    Cola, Adriano; Farella, Isabella

    2014-11-17

    The perturbation behaviour of Ohmic and Schottky CdTe detectors under strong optical pulses is investigated. To this scope, the electric field profiles and the induced charge transients are measured, thus simultaneously addressing fixed and free charges properties, interrelated by one-carrier trapping. The results elucidate the different roles of the contacts and deep levels, both under dark and strong irradiation conditions, and pave the way for the improvement of detector performance control under high X-ray fluxes.

  18. Development of a Spectral Model Based on Charge Transport for the Swift/BAT 32K CdZnTe Detector Array

    NASA Technical Reports Server (NTRS)

    Sato, Goro; Parsons, Ann; Hillinger, Derek; Suzuki, Masaya; Takahashi, Tadayuki; Tashiro, Makoto; Nakazawa, Kazuhiro; Okada, Yuu; Takahashi, Hiromitsu; Watanabe, Shin

    2005-01-01

    The properties of 32K CdZnTe (4 x 4 sq mm large, 2 mm thick) detectors have been studied in the pre-flight calibration of the Burst Alert Telescope (BAT) on-board the Swift Gamma-ray Burst Explorer (scheduled for launch in November 2004). In order to understand the energy response of the BAT CdZnTe array, we first quantify the mobility-lifetime (mu tau) products of carriers in individual CdZnTe detectors, which produce a position dependency in the charge induction efficiency and results in a low energy tail in the energy spectrum. Based on a new method utilizing (57)Co spectra obtained at different bias voltages, the mu tau for electrons ranges from 5.0 x 10(exp -4) to 1.0 x 10(exp -2) sq cm/V while the mu tau for holes ranges from 1.3 x 10(exp -5 to 1.8 x 10(exp -4) sq cm/V. We find that this wide distribution of mu tau products explains the large diversity in spectral shapes between CdZnTe detectors well. We also find that the variation of mu tau products can be attributed to the difference of crystal ingots or manufacturing harness. We utilize the 32K sets of extracted mu tau products to develop a spectral model of the detector. In combination with Monte Carlo simulations, we can construct a spectral model for any photon energy or any incident angle.

  19. CdTe detector efficiency calibration using thick targets of pure and stable compounds

    NASA Astrophysics Data System (ADS)

    Chaves, P. C.; Taborda, A.; Reis, M. A.

    2012-02-01

    Quantitative PIXE measurements require perfectly calibrated set-ups. Cooled CdTe detectors have good efficiency for energies above those covered by Si(Li) detectors and turn on the possibility of studying K X-rays lines instead of L X-rays lines for medium and eventually heavy elements, which is an important advantage in various cases, if only limited resolution systems are available in the low energy range. In this work we present and discuss spectra from a CdTe semiconductor detector covering the energy region from Cu (K α1 = 8.047 keV) to U (K α1 = 98.439 keV). Pure thick samples were irradiated with proton beams at the ITN 3.0 MV Tandetron accelerator in the High Resolution High Energy PIXE set-up. Results and the application to the study of a Portuguese Ossa Morena region Dark Stone sample are presented in this work.

  20. Growth and fabrication method of CdTe and its performance as a radiation detector

    NASA Astrophysics Data System (ADS)

    Choi, Hyojeong; Jeong, Manhee; Kim, Han Soo; Kim, Young Soo; Ha, Jang Ho; Chai, Jong-Seo

    2015-01-01

    A CdTe crystal ingot doped with 2000 ppm of Cl was grown by using the low-pressure Bridgman (LPB) method at the Korea Atomic Energy Research Institute (KAERI). A Semiconductor detector as a radiation detection sensor with a size of 7 (W) × 6.5 (D) × 2 (H) mm3 was fabricated from the CdTe ingot. In addition, the properties of the CdTe sample were observed through four kinds of experiments to analyze its performance. The resistivity was obtained as 1.41 × 1010 Ωcm by using a Keithley 6517A high-precision electrometer. The mobility-lifetime products for electrons and holes were 3.137 × 10-4 cm2/V and 4.868 × 10-5 cm2/V, respectively. Finally, we achieved a 16.8% energy resolution at 59.5 keV for the 241Am gamma-ray source. The CdTe semiconductor detector grown at KAERI has a performance good enough to detect low-energy gamma-rays.

  1. Evaluation of XRI-UNO CdTe detector for nuclear medical imaging

    NASA Astrophysics Data System (ADS)

    Jambi, L. K.; Lees, J. E.; Bugby, S. L.; Tipper, S.; Alqahtani, M. S.; Perkins, A. C.

    2015-06-01

    Over the last two decades advances in semiconductor detector technology have reached the point where they are sufficiently sensitive to become an alternative to scintillators for high energy gamma ray detection for application in fields such as medical imaging. This paper assessed the Cadmium-Telluride (CdTe) XRI-UNO semiconductor detector produced by X-RAY Imatek for photon energies of interest in nuclear imaging. The XRI-UNO detector was found to have an intrinsic spatial resolution of <0.5mm and a high incident count rate capability up to at least 1680cps. The system spatial resolution, uniformity and sensitivity characteristics are also reported.

  2. Energy and coincidence time resolution measurements of CdTe detectors for PET.

    PubMed

    Ariño, G; Chmeissani, M; De Lorenzo, G; Puigdengoles, C; Cabruja, E; Calderón, Y; Kolstein, M; Macias-Montero, J G; Martinez, R; Mikhaylova, E; Uzun, D

    2013-02-01

    We report on the characterization of 2 mm thick CdTe diode detector with Schottky contacts to be employed in a novel conceptual design of PET scanner. Results at -8°C with an applied bias voltage of -1000 V/mm show a 1.2% FWHM energy resolution at 511 keV. Coincidence time resolution has been measured by triggering on the preamplifier output signal to improve the timing resolution of the detector. Results at the same bias and temperature conditions show a FWHM of 6 ns with a minimum acceptance energy of 500 keV. These results show that pixelated CdTe Schottky diode is an excellent candidate for the development of next generation nuclear medical imaging devices such as PET, Compton gamma cameras, and especially PET-MRI hybrid systems when used in a magnetic field immune configuration.

  3. A 12-bit 1 MS/s SAR-ADC for multi-channel CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Wei, Liu; Tingcun, Wei; Bo, Li; Panjie, Guo; Yongcai, Hu

    2015-04-01

    This paper presents a low power, area-efficient and radiation-hardened 12-bit 1 MS/s successive approximation register (SAR) analog-to-digital converter (ADC) for multi-channel CdZnTe (CZT) detector applications. In order to improve the SAR-ADC's accuracy, a novel comparator is proposed in which the offset voltage is self-calibrated and also a new architecture for the unit capacitor array is proposed to reduce the capacitance mismatches in the charge-redistribution DAC. The ability to radiation-harden the SAR-ADC is enhanced through circuit and layout design technologies. The prototype chip was fabricated using a TSMC 0.35 μm 2P4M CMOS process. At a 3.3/5 V power supply and a sampling rate of 1 MS/s, the proposed SAR-ADC achieves a peak signal to noise and distortion ratio (SINAD) of 67.64 dB and consumes only 10 mW power. The core of the prototype chip occupies an active area of 1180 × 1080 μm2. Project supported by the Special-Funded Program on National Key Scientific Instruments and Equipment Development (No. 2011YQ040082).

  4. CdZnTe detector for hard x-ray and low energy gamma-ray focusing telescope

    NASA Astrophysics Data System (ADS)

    Natalucci, L.; Alvarez, J. M.; Barriere, N.; Caroli, E.; Curado da Silva, R. M.; Del Sordo, S.; Di Cosimo, S.; Frutti, M.; Hernanz, M.; Lozano, M.; Quadrini, E.; Pellegrini, G.; Stephen, J. B.; Ubertini, P.; Uslenghi, M. C.; Zoglauer, A.

    2008-07-01

    The science drivers for a new generation soft gamma-ray mission are naturally focused on the detailed study of the acceleration mechanisms in a variety of cosmic sources. Through the development of high energy optics in the energy energy range 0.05-1 MeV it will be possible to achieve a sensitivity about two orders of magnitude better than the currently operating gamma-ray telescopes. This will open a window for deep studies of many classes of sources: from Galactic X-ray binaries to magnetars, from supernova remnants to Galaxy clusters, from AGNs (Seyfert, blazars, QSO) to the determination of the origin of the hard X-/gamma-ray cosmic background, from the study of antimatter to that of the dark matter. In order to achieve the needed performance, a detector with mm spatial resolution and very high peak efficiency is needed. The instrumental characteristics of this device could eventually allow to detect polarization in a number of objects including pulsars, GRBs and bright AGNs. In this work we focus on the characteristics of the focal plane detector, based on CZT or CdTe semiconductor sensors arranged in multiple planes and viewed by a side detector to enhance gamma-ray absorption in the Compton regime. We report the preliminary results of an optimization study based on simulations and laboratory tests, as prosecution of the former design studies of the GRI mission which constitute the heritage of this activity.

  5. Super-resolution x-ray imaging by CdTe discrete detector arrays

    NASA Astrophysics Data System (ADS)

    Aoki, T.; Ishida, Y.; Morii, H.; Tomita, Y.; Ohashi, G.; Temmyo, J.; Hatanaka, Y.

    2005-08-01

    512-pixel CdTe super-liner imaging scanner was developed. This device was consist with 512 chips of M-π-n CdTe diode detector fabricated by excimer laser doping process, 8 chips of photon-counting mode 64ch ASIC with FPGA circuit, USB2.0 interface with 1-CPU. It has 5 discriminated levels and over 2Mcps count rate for X-ray penetration imaging. This imaging scanner has 512 discrete CdTe chips for detector arrays with the length of 2.0mm, width of 0.8mm and thickness of 0.5mm. These chips were mounted in four plover array rows for high-resolution imaging with 0.5mm-pitch, therefore the pixel pitch was over the pixel width. When images were taken with scanning system with this arrays, we could obtain over-resolution than pixel width. In this paper, this "over-resolution" imaging will be called "super resolution imaging". In high-resolution imaging device, the pixel devices on one substrate were formed by integrated process, or many discrete detector chips were installed on circuit board, usually. In the latter case, it is easer to make each detector chips than former case, and it are no need to consider charge sharing phenomena compare with one-chip pixel devices. However, a decrease in pixel pitch makes the mount to the detector chip to the ASIC board difficult because the handling will also be difficult The super-resolution technique in this scanner by pixel-shift method for X-ray imaging is shown in this paper

  6. Evaluation of a Compton scattering camera using 3-D position sensitive CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Du, Y. F.; He, Z.; Knoll, G. F.; Wehe, D. K.; Li, W.

    2001-01-01

    A CZT Compton Camera (CCC) is being built using two three-dimensional (3-D) position-sensitive CZT detectors. Expected system performance was analyzed by analytical and Monte Carlo approaches. Based on the measurement of detector energy and position resolution, the expected angular resolution is ˜3° and ˜2° for a ±30° FOV for 511 keV and 1 MeV γ-rays, respectively. The intrinsic efficiency for a point source 10 cm from the first detector surface ranges from 1.5×10 -4 to 8.8×10 -6 for 500 keV-3 MeV.

  7. Study of the effect of the stress on CdTe nuclear detectors

    SciTech Connect

    Ayoub, M.; Radley, I.; Mullins, J. T.; Hage-Ali, M.

    2013-09-14

    CdTe detectors are commonly used for X and γ ray applications. The performance of these detectors is strongly affected by different types of mechanical stress; such as that caused by differential expansion between the semiconductor and its intimate metallic contacts and that caused by applied pressure during the bonding process. The aim of this work was to study the effects of stress on the performance of CdTe detectors. A difference in expansion coefficients induces transverse stress under the metallic contact, while contact pressure induces longitudinal stress. These stresses have been simulated by applying known static pressures. For the longitudinal case, the pressure was applied directly to the metallic contact; while in the transverse case, it was applied to the side. We have studied the effect of longitudinal and transverse stresses on the electrical characteristics including leakage current measurements and γ-ray detection performance. We have also investigated induced defects, their nature, activation energies, cross sections, and concentrations under the applied stress by using photo-induced current transient spectroscopy and thermoelectric effect spectroscopy techniques. The operational stress limit is also given.

  8. Evaluation of Compton gamma camera prototype based on pixelated CdTe detectors.

    PubMed

    Calderón, Y; Chmeissani, M; Kolstein, M; De Lorenzo, G

    2014-06-01

    A proposed Compton camera prototype based on pixelated CdTe is simulated and evaluated in order to establish its feasibility and expected performance in real laboratory tests. The system is based on module units containing a 2×4 array of square CdTe detectors of 10×10 mm(2) area and 2 mm thickness. The detectors are pixelated and stacked forming a 3D detector with voxel sizes of 2 × 1 × 2 mm(3). The camera performance is simulated with Geant4-based Architecture for Medicine-Oriented Simulations(GAMOS) and the Origin Ensemble(OE) algorithm is used for the image reconstruction. The simulation shows that the camera can operate with up to 10(4) Bq source activities with equal efficiency and is completely saturated at 10(9) Bq. The efficiency of the system is evaluated using a simulated (18)F point source phantom in the center of the Field-of-View (FOV) achieving an intrinsic efficiency of 0.4 counts per second per kilobecquerel. The spatial resolution measured from the point spread function (PSF) shows a FWHM of 1.5 mm along the direction perpendicular to the scatterer, making it possible to distinguish two points at 3 mm separation with a peak-to-valley ratio of 8.

  9. A low-noise 64-channel front-end readout ASIC for CdZnTe detectors aimed to hard X-ray imaging systems

    NASA Astrophysics Data System (ADS)

    Gan, B.; Wei, T.; Gao, W.; Liu, H.; Hu, Y.

    2016-04-01

    In this paper, we report on the recent development of a 64-channel low-noise front-end readout ASIC for CdZnTe detectors aimed to hard X-ray imaging systems. The readout channel is comprised of a charge sensitive amplifier, a leakage current compensation circuit, a CR-RC shaper, two S-K filters, an inverse proportional amplifier, a peak-detect-and-hold circuit, a discriminator and trigger logic, a time sequence control circuit and a driving buffer. The readout ASIC is implemented in TSMC 0.35 μm mixed-signal CMOS technology, the die size of the prototype chip is 2.7 mm×8.0 mm. The overall gain of the readout channel is 200 mV/fC, the power consumption is less than 8 mW/channel, the linearity error is less than 1%, the inconsistency among the channels is less than 2.86%, and the equivalent noise charge of a typical channel is 66 e- at zero farad plus 14 e- per picofarad. By connecting this readout ASIC to an 8×8 pixel CdZnTe detector, we obtained an energy spectrum, the energy resolution of which is 4.5% at the 59.5 keV line of 241Am source.

  10. Primary study on the contact degradation mechanism of CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Sang, Wenbin; Wei, Jin; Qi, Zhang; Wanwan, Li; Jiahua, Min; Jianyong, Teng; Yongbiao, Qian

    2004-07-01

    The metal-CdZnTe (CZT) interface plays a vital role in determining the contact characteristics, which is often the dominant factor influencing detector performance. The effects of the degradation of the interfacial layer between the metal contact layer and CZT surface on the mechanical and electrical properties have been investigated in this paper. The interfacial thermal stresses were simulated using 3-D finite element method (FEM). The results indicate that the maximum thermal stress is concentrated on the midst of the electrode and the magnitude of the stress produced by the different electrode materials in order is Al>Au>Pt>In. The adhesion forces between the metal contact layer and CZT surface were measured by using a Dage PC2400 Micro tester with the shear-off-method. The inter-diffusion between the metal contact layer and CZT was identified using the Anger depth profiles. The experimental results indicate that the electroless Au electrode on p-type high resistivity CZT is of smaller interfacial adhesion strength, but of better ohmicity than the sputtered Au. In addition, the aging effects on the contact characteristics of the detector were also examined.

  11. Final Report: A CdZnTe detector for MRI-compatible SPECT Systems

    SciTech Connect

    Meng, Ling-Jian

    2012-12-27

    The key objective of this project is to develop the enabling technology for future MRI-compatible nuclear (e.g. SPECT) imaging system, and to demonstrate the feasibility of performing simultaneous MR and SPECT imaging studies of the same object. During the past three years, we have developed (a) a MRI-compatible ultrahigh resolution gamma ray detector and associated readout electronics, (b) a theoretical approach for modeling the effect of strong magnetic field on SPECT image quality, and (c) a maximum-likelihood (ML) based reconstruction routine with correction for the MR-induced distortion. With this support, we have also constructed a four-head MR-compatible SPECT system and tested the system inside a 3-T clinical MR-scanner located on UI campus. The experimental results obtained with this system have clearly demonstrated that sub-500um spatial resolution can be achieved with a SPECT system operated inside a 3-T MRI scanner. During the past three years, we have accomplished most of the major objectives outlined in the original proposal. These research efforts have laid out a solid foundation the development of future MR-compatible SPECT systems for both pre-clinical and clinical imaging applications.

  12. CdTe focal plane detector for hard x-ray focusing optics

    NASA Astrophysics Data System (ADS)

    Seller, Paul; Wilson, Matthew D.; Veale, Matthew C.; Schneider, Andreas; Gaskin, Jessica; Wilson-Hodge, Colleen; Christe, Steven; Shih, Albert Y.; Gregory, Kyle; Inglis, Andrew; Panessa, Marco

    2015-08-01

    The demand for higher resolution x-ray optics (a few arcseconds or better) in the areas of astrophysics and solar science has, in turn, driven the development of complementary detectors. These detectors should have fine pixels, necessary to appropriately oversample the optics at a given focal length, and an energy response also matched to that of the optics. Rutherford Appleton Laboratory have developed a 3-side buttable, 20 mm x 20 mm CdTe-based detector with 250 μm square pixels (80x80 pixels) which achieves 1 keV FWHM @ 60 keV and gives full spectroscopy between 5 keV and 200 keV. An added advantage of these detectors is that they have a full-frame readout rate of 10 kHz. Working with NASA Goddard Space Flight Center and Marshall Space Flight Center, 4 of these 1mm-thick CdTe detectors are tiled into a 2x2 array for use at the focal plane of a balloon-borne hard-x-ray telescope, and a similar configuration could be suitable for astrophysics and solar space-based missions. This effort encompasses the fabrication and testing of flightsuitable front-end electronics and calibration of the assembled detector arrays. We explain the operation of the pixelated ASIC readout and measurements, front-end electronics development, preliminary X-ray imaging and spectral performance, and plans for full calibration of the detector assemblies. Work done in conjunction with the NASA Centers is funded through the NASA Science Mission Directorate Astrophysics Research and Analysis Program.

  13. CdTe Focal Plane Detector for Hard X-Ray Focusing Optics

    NASA Technical Reports Server (NTRS)

    Seller, Paul; Wilson, Matthew D.; Veale, Matthew C.; Schneider, Andreas; Gaskin, Jessica; Wilson-Hodge, Colleen; Christe, Steven; Shih, Albert Y.; Inglis, Andrew; Panessa, Marco

    2015-01-01

    The demand for higher resolution x-ray optics (a few arcseconds or better) in the areas of astrophysics and solar science has, in turn, driven the development of complementary detectors. These detectors should have fine pixels, necessary to appropriately oversample the optics at a given focal length, and an energy response also matched to that of the optics. Rutherford Appleton Laboratory have developed a 3-side buttable, 20 millimeter x 20 millimeter CdTe-based detector with 250 micrometer square pixels (80 x 80 pixels) which achieves 1 kiloelectronvolt FWHM (Full-Width Half-Maximum) @ 60 kiloelectronvolts and gives full spectroscopy between 5 kiloelectronvolts and 200 kiloelectronvolts. An added advantage of these detectors is that they have a full-frame readout rate of 10 kilohertz. Working with NASA Goddard Space Flight Center and Marshall Space Flight Center, 4 of these 1 millimeter-thick CdTe detectors are tiled into a 2 x 2 array for use at the focal plane of a balloon-borne hard-x-ray telescope, and a similar configuration could be suitable for astrophysics and solar space-based missions. This effort encompasses the fabrication and testing of flight-suitable front-end electronics and calibration of the assembled detector arrays. We explain the operation of the pixelated ASIC readout and measurements, front-end electronics development, preliminary X-ray imaging and spectral performance, and plans for full calibration of the detector assemblies. Work done in conjunction with the NASA Centers is funded through the NASA Science Mission Directorate Astrophysics Research and Analysis Program.

  14. Development of mammography system using CdTe photon counting detector for the exposure dose reduction

    NASA Astrophysics Data System (ADS)

    Maruyama, Sho; Niwa, Naoko; Yamazaki, Misaki; Yamakawa, Tsutomu; Nagano, Tatsuya; Kodera, Yoshie

    2014-03-01

    We propose a new mammography system using a cadmium telluride (CdTe) photon-counting detector for exposure dose reduction. In contrast to conventional mammography, this system uses high-energy X-rays. This study evaluates the usefulness of this system in terms of the absorbed dose distribution and contrast-to-noise ratio (CNR) at acrylic step using a Monte Carlo simulation. In addition, we created a prototype system that uses a CdTe detector and automatic movement stage. For various conditions, we measured the properties and evaluated the quality of images produced by the system. The simulation result for a tube voltage of 40 kV and tungsten/barium (W/Ba) as a target/filter shows that the surface dose was reduced more than 60% compared to that under conventional conditions. The CNR of our proposal system also became higher than that under conventional conditions. The point at which the CNRs coincide for 4 cm polymethyl methacrylate (PMMA) at the 2-mm-thick step corresponds to a dose reduction of 30%, and these differences increased with increasing phantom thickness. To improve the image quality, we determined the problematic aspects of the scanning system. The results of this study indicate that, by using a higher X-ray energy than in conventional mammography, it is possible to obtain a significant exposure dose reduction without loss of image quality. Further, the image quality of the prototype system can be improved by optimizing the balance between the shift-and-add operation and the output of the X-ray tube. In future work, we will further examine these improvement points.

  15. Modeling and simulation of Positron Emission Mammography (PEM) based on double-sided CdTe strip detectors

    NASA Astrophysics Data System (ADS)

    Ozsahin, I.; Unlu, M. Z.

    2014-03-01

    Breast cancer is the most common leading cause of cancer death among women. Positron Emission Tomography (PET) Mammography, also known as Positron Emission Mammography (PEM), is a method for imaging primary breast cancer. Over the past few years, PEMs based on scintillation crystals dramatically increased their importance in diagnosis and treatment of early stage breast cancer. However, these detectors have significant limitations like poor energy resolution resulting with false-negative result (missed cancer), and false-positive result which leads to suspecting cancer and suggests an unnecessary biopsy. In this work, a PEM scanner based on CdTe strip detectors is simulated via the Monte Carlo method and evaluated in terms of its spatial resolution, sensitivity, and image quality. The spatial resolution is found to be ~ 1 mm in all three directions. The results also show that CdTe strip detectors based PEM scanner can produce high resolution images for early diagnosis of breast cancer.

  16. Use of high-granularity CdZnTe pixelated detectors to correct response non-uniformities caused by defects in crystals

    NASA Astrophysics Data System (ADS)

    Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; De Geronimo, G.; Eger, J.; Emerick, A.; Fried, J.; Hossain, A.; Roy, U.; Salwen, C.; Soldner, S.; Vernon, E.; Yang, G.; James, R. B.

    2016-01-01

    Following our successful demonstration of the position-sensitive virtual Frisch-grid detectors, we investigated the feasibility of using high-granularity position sensing to correct response non-uniformities caused by the crystal defects in CdZnTe (CZT) pixelated detectors. The development of high-granularity detectors able to correct response non-uniformities on a scale comparable to the size of electron clouds opens the opportunity of using unselected off-the-shelf CZT material, whilst still assuring high spectral resolution for the majority of the detectors fabricated from an ingot. Here, we present the results from testing 3D position-sensitive 15×15×10 mm3 pixelated detectors, fabricated with conventional pixel patterns with progressively smaller pixel sizes: 1.4, 0.8, and 0.5 mm. We employed the readout system based on the H3D front-end multi-channel ASIC developed by BNL's Instrumentation Division in collaboration with the University of Michigan. We use the sharing of electron clouds among several adjacent pixels to measure locations of interaction points with sub-pixel resolution. By using the detectors with small-pixel sizes and a high probability of the charge-sharing events, we were able to improve their spectral resolutions in comparison to the baseline levels, measured for the 1.4-mm pixel size detectors with small fractions of charge-sharing events. These results demonstrate that further enhancement of the performance of CZT pixelated detectors and reduction of costs are possible by using high spatial-resolution position information of interaction points to correct the small-scale response non-uniformities caused by crystal defects present in most devices.

  17. Use of high-granularity CdZnTe pixelated detectors to correct response non-uniformities caused by defects in crystals

    DOE PAGES

    Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; De Geronimo, G.; Eger, J.; Emerick, A.; Fried, J.; Hossain, A.; Roy, U.; Salwen, C.; et al

    2015-09-06

    Following our successful demonstration of the position-sensitive virtual Frisch-grid detectors, we investigated the feasibility of using high-granularity position sensing to correct response non-uniformities caused by the crystal defects in CdZnTe (CZT) pixelated detectors. The development of high-granularity detectors able to correct response non-uniformities on a scale comparable to the size of electron clouds opens the opportunity of using unselected off-the-shelf CZT material, whilst still assuring high spectral resolution for the majority of the detectors fabricated from an ingot. Here, we present the results from testing 3D position-sensitive 15×15×10 mm3 pixelated detectors, fabricated with conventional pixel patterns with progressively smaller pixelmore » sizes: 1.4, 0.8, and 0.5 mm. We employed the readout system based on the H3D front-end multi-channel ASIC developed by BNL's Instrumentation Division in collaboration with the University of Michigan. We use the sharing of electron clouds among several adjacent pixels to measure locations of interaction points with sub-pixel resolution. By using the detectors with small-pixel sizes and a high probability of the charge-sharing events, we were able to improve their spectral resolutions in comparison to the baseline levels, measured for the 1.4-mm pixel size detectors with small fractions of charge-sharing events. These results demonstrate that further enhancement of the performance of CZT pixelated detectors and reduction of costs are possible by using high spatial-resolution position information of interaction points to correct the small-scale response non-uniformities caused by crystal defects present in most devices.« less

  18. Use of high-granularity CdZnTe pixelated detectors to correct response non-uniformities caused by defects in crystals

    SciTech Connect

    Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; De Geronimo, G.; Eger, J.; Emerick, A.; Fried, J.; Hossain, A.; Roy, U.; Salwen, C.; Soldner, S.; Vernon, E.; Yang, G.; James, R. B.

    2015-09-06

    Following our successful demonstration of the position-sensitive virtual Frisch-grid detectors, we investigated the feasibility of using high-granularity position sensing to correct response non-uniformities caused by the crystal defects in CdZnTe (CZT) pixelated detectors. The development of high-granularity detectors able to correct response non-uniformities on a scale comparable to the size of electron clouds opens the opportunity of using unselected off-the-shelf CZT material, whilst still assuring high spectral resolution for the majority of the detectors fabricated from an ingot. Here, we present the results from testing 3D position-sensitive 15×15×10 mm3 pixelated detectors, fabricated with conventional pixel patterns with progressively smaller pixel sizes: 1.4, 0.8, and 0.5 mm. We employed the readout system based on the H3D front-end multi-channel ASIC developed by BNL's Instrumentation Division in collaboration with the University of Michigan. We use the sharing of electron clouds among several adjacent pixels to measure locations of interaction points with sub-pixel resolution. By using the detectors with small-pixel sizes and a high probability of the charge-sharing events, we were able to improve their spectral resolutions in comparison to the baseline levels, measured for the 1.4-mm pixel size detectors with small fractions of charge-sharing events. These results demonstrate that further enhancement of the performance of CZT pixelated detectors and reduction of costs are possible by using high spatial-resolution position information of interaction points to correct the small-scale response non-uniformities caused by crystal defects present in most devices.

  19. Imaging of Ra-223 with a small-pixel CdTe detector

    NASA Astrophysics Data System (ADS)

    Scuffham, J. W.; Pani, S.; Seller, P.; Sellin, P. J.; Veale, M. C.; Wilson, M. D.; Cernik, R. J.

    2015-01-01

    Ra-223 Dichloride (Xofigo™) is a promising new radiopharmaceutical offering survival benefit and palliation of painful bone metastases in patients with hormone-refractory prostate cancer [1]. The response to radionuclide therapy and toxicity are directly linked to the absorbed radiation doses to the tumour and organs at risk respectively. Accurate dosimetry necessitates quantitative imaging of the biodistribution and kinetics of the radiopharmaceutical. Although primarily an alpha-emitter, Ra-223 also has some low-abundance X-ray and gamma emissions, which enable imaging of the biodistribution in the patient. However, the low spectral resolution of conventional gamma camera detectors makes in-vivo imaging of Ra-223 challenging. In this work, we present spectra and image data of anthropomorphic phantoms containing Ra-223 acquired with a small-pixel CdTe detector (HEXITEC) [2] with a pinhole collimator. Comparison is made with similar data acquired using a clinical gamma camera. The results demonstrate the advantages of the solid state detector in terms of scatter rejection and quantitative accuracy of the images. However, optimised collimation is needed in order for the sensitivity to rival current clinical systems. As different dosage levels and administration regimens for this drug are explored in current clinical trials, there is a clear need to develop improved imaging technologies that will enable personalised treatments to be designed for patients.

  20. Room temperature semiconductor detectors for safeguards measurements

    NASA Astrophysics Data System (ADS)

    Arlt, R.; Rundquist, D. E.

    A summary is given of the principal areas of application where CdTe detectors are presently used by the IAEA in nuclear material safeguards. Hemispheric detectors with a sensitive volume of about 20 mm 3 have their principal application in the verification of irradiated nuclear material. Larger volume hemispheric detectors are used for the verification of unirradiated material. Their availability, however, is still limited. Problems with the commercial supply of detectors and with ruggedizing the design of the miniature detection probes need to be solved. New results which are relevant for future applications are described. It has been shown that hemispheric detectors made of CdZnTe provide a resolution of 3-4% and a peak/Compton ratio larger than two for 137Cs. Large volume planar CdZnTe have been used in conjunction with pulse shape discrimination electronics. The detector efficiency, however, still remains below the values expected from their geometric dimensions. A new technique to achieve single charge collection in large volume CdZnTe detectors has been developed. Planar detectors with PIN structure and Peltier cooling have further improved. However, the problem of long term stability has not been solved yet. Silicon detectors are increasingly used in unattended radiation monitoring systems. They have a proven long term stability and can cover a signal range of 5-6 decades if used with fast pulse counting electronics.

  1. A 10 cm × 10 cm CdTe Spectroscopic Imaging Detector based on the HEXITEC ASIC

    NASA Astrophysics Data System (ADS)

    Wilson, M. D.; Dummott, L.; Duarte, D. D.; Green, F. H.; Pani, S.; Schneider, A.; Scuffham, J. W.; Seller, P.; Veale, M. C.

    2015-10-01

    The 250 μ m pitch 80x80 pixel HEXITEC detector systems have shown that spectroscopic imaging with an energy resolution of <1 keV FWHM per pixel can be readily achieved in the range of 5-200 keV with Al-pixel CdTe biased to -500 V. This level of spectroscopic imaging has a variety of applications but the ability to produce large area detectors remains a barrier to the adoption of this technology. The limited size of ASICs and defect free CdTe wafers dictates that building large area monolithic detectors is not presently a viable option. A 3-side buttable detector module has been developed to cover large areas with arrays of smaller detectors. The detector modules are 20.35 × 20.45 mm with CdTe bump bonded to the HEXITEC ASIC with coverage up to the edge of the module on three sides. The fourth side has a space of 3 mm to allow I/O wire bonds to be made between the ASIC and the edge of a PCB that routes the signals to a connector underneath the active area of the module. The detector modules have been assembled in rows of five modules with a dead space of 170 μ m between each module. Five rows of modules have been assembled in a staggered height array where the wire bonds of one row of modules are covered by the active detector area of a neighboring row. A data acquisition system has been developed to digitise, store and output the 24 Gbit/s data that is generated by the array. The maximum bias magnitude that could be applied to the CdTe detectors from the common voltage source was limited by the worst performing detector module. In this array of detectors a bias of -400 V was used and the detector modules had 93 % of pixels with better than 1.2 keV FWHM at 59.5 keV. An example of K-edge enhanced imaging for mammography was demonstrated. Subtracting images from the events directly above and below the K-edge of the Iodine contrast agent was able to extract the Iodine information from the image of a breast phantom and improve the contrast of the images. This is just

  2. Drift time variations in CdZnTe detectors measured with alpha-particles: Their correlation with the detector’s responses

    SciTech Connect

    Bolotnikov A. E.; Butcher, J.; Hamade, M.; Petryk, M.; Bolotnikov, A.; Camarda, G.; Cui, Y.; Hossain, A.; Kim, K.; Yang, G.; and James, R.

    2012-05-14

    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 that 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.

  3. Possible use of CdTe detectors in kVp monitoring of diagnostic x-ray tubes

    PubMed Central

    Krmar, M.; Bucalović, N.; Baucal, M.; Jovančević, N.

    2010-01-01

    It has been suggested that kVp of diagnostic X-ray devices (or maximal energy of x-ray photon spectra) should be monitored routinely; however a standardized noninvasive technique has yet to be developed and proposed. It is well known that the integral number of Compton scattered photons and the intensities of fluorescent x-ray lines registered after irradiation of some material by an x-ray beam are a function of the maximal beam energy. CdTe detectors have sufficient energy resolution to distinguish individual x-ray fluorescence lines and high efficiency for the photon energies in the diagnostic region. Our initial measurements have demonstrated that the different ratios of the integral number of Compton scattered photons and intensities of K and L fluorescent lines detected by CdTe detector are sensitive function of maximal photon energy and could be successfully applied for kVp monitoring. PMID:21037976

  4. Use of the drift-time method to measure the electron lifetime in long-drift-length CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Bolotnikov, A. E.; Camarda, G. S.; Chen, E.; Gul, R.; Dedic, V.; De Geronimo, G.; Fried, J.; Hossain, A.; MacKenzie, J. M.; Ocampo, L.; Sellin, P.; Taherion, S.; Vernon, E.; Yang, G.; El-Hanany, U.; James, R. B.

    2016-09-01

    The traditional method for electron lifetime measurements of CdZnTe (CZT) detectors relies on using the Hecht equation. The procedure involves measuring the dependence of the detector response on the applied bias to evaluate the μτ product, which in turn can be converted into the carrier lifetime. Despite general acceptance of this technique, which is very convenient for comparative testing of different CZT materials, the assumption of a constant electric field inside a detector is unjustified. In the Hecht equation, this assumption means that the drift time would be a linear function of the distance. This condition is not fulfilled in practice at low applied biases, where the Hecht equation is most sensitive to the μτ product. As a result, researchers usually take measurements at relatively high biases, which work well in the case of the low μτ-product material, <10-3 cm2/V, but give significantly underestimated values for the case of high μτ-product crystals. In this work, we applied the drift-time method to measure the electron lifetimes in long-drift-length (4 cm) standard-grade CZT detectors produced by the Redlen Technologies. We found that the electron μτ product of tested crystals is in the range 0.1-0.2 cm2/V, which is an order of the magnitude higher than any value previously reported for a CZT material. In comparison, using the Hecht equation fitting, we obtained μτ = 2.3 × 10-2 cm2/V for a 2-mm thin planar detector fabricated from the same CZT material.

  5. Development of a CdTe pixel detector with a window comparator ASIC for high energy X-ray applications

    NASA Astrophysics Data System (ADS)

    Hirono, T.; Toyokawa, H.; Furukawa, Y.; Honma, T.; Ikeda, H.; Kawase, M.; Koganezawa, T.; Ohata, T.; Sato, M.; Sato, G.; Takagaki, M.; Takahashi, T.; Watanabe, S.

    2011-09-01

    We have developed a photon-counting-type CdTe pixel detector (SP8-01). SP8-01 was designed as a prototype of a high-energy X-ray imaging detector for experiments using synchrotron radiation. SP8-01 has a CdTe sensor of 500 μm thickness, which has an absorption efficiency of almost 100% up to 50 keV and 45% even at 100 keV. A full-custom application specific integrated circuit (ASIC) was designed as a readout circuit of SP8-01, which is equipped with a window-type discriminator. The upper discriminator realizes a low-background measurement, because X-ray beams from the monochromator contain higher-order components beside the fundamental X-rays in general. ASIC chips were fabricated with a TSMC 0.25 μm CMOS process, and CdTe sensors were bump-bonded to the ASIC chips by a gold-stud bonding technique. Beam tests were performed at SPring-8. SP8-01 detected X-rays up to 120 keV. The capability of SP8-01 as an imaging detector for high-energy X-ray synchrotron radiation was evaluated with its performance characteristics.

  6. X-ray response of CdZnTe detectors grown by the vertical Bridgman technique: Energy, temperature and high flux effects

    NASA Astrophysics Data System (ADS)

    Abbene, L.; Gerardi, G.; Turturici, A. A.; Raso, G.; Benassi, G.; Bettelli, M.; Zambelli, N.; Zappettini, A.; Principato, F.

    2016-11-01

    Nowadays, CdZnTe (CZT) is one of the key materials for the development of room temperature X-ray and gamma ray detectors and great efforts have been made on both the device and the crystal growth technologies. In this work, we present the results of spectroscopic investigations on new boron oxide encapsulated vertical Bridgman (B-VB) grown CZT detectors, recently developed at IMEM-CNR Parma, Italy. Several detectors, with the same electrode layout (gold electroless contacts) and different thicknesses (1 and 2.5 mm), were realized: the cathode is a planar electrode covering the detector surface (4.1×4.1 mm2), while the anode is a central electrode (2×2 mm2) surrounded by a guard-ring electrode. The detectors are characterized by electron mobility-lifetime product (μeτe) values ranging between 0.6 and 1·10-3 cm2/V and by low leakage currents at room temperature and at high bias voltages (38 nA/cm2 at 10000 V/cm). The spectroscopic response of the detectors to monochromatic X-ray and gamma ray sources (109Cd, 241Am and 57Co), at different temperatures and fluxes (up to 1 Mcps), was measured taking into account the mitigation of the effects of incomplete charge collection, pile-up and high flux radiation induced polarization phenomena. A custom-designed digital readout electronics, developed at DiFC of University of Palermo (Italy), able to perform a fine pulse shape and height analysis even at high fluxes, was used. At low rates (200 cps) and at room temperature (T=25 °C), the detectors exhibit an energy resolution FWHM around 4% at 59.5 keV, for comparison an energy resolution of 3% was measured with Al/CdTe/Pt detectors by using the same electronics (A250F/NF charge sensitive preamplifier, Amptek, USA; nominal ENC of 100 electrons RMS). At high rates (750 kcps), energy resolution values of 7% and 9% were measured, with throughputs of 2% and 60% respectively. No radiation polarization phenomena were observed at room temperature up to 1 Mcps (241Am source, 60 ke

  7. Development of a simplified simulation model for performance characterization of a pixellated CdZnTe multimodality imaging system

    NASA Astrophysics Data System (ADS)

    Guerra, P.; Santos, A.; Darambara, D. G.

    2008-02-01

    Current requirements of molecular imaging lead to the complete integration of complementary modalities in a single hybrid imaging system to correlate function and structure. Among the various existing detector technologies, which can be implemented to integrate nuclear modalities (PET and/or single-photon emission computed tomography with x-rays (CT) and most probably with MR, pixellated wide bandgap room temperature semiconductor detectors, such as CdZnTe and/or CdTe, are promising candidates. This paper deals with the development of a simplified simulation model for pixellated semiconductor radiation detectors, as a first step towards the performance characterization of a multimodality imaging system based on CdZnTe. In particular, this work presents a simple computational model, based on a 1D approximate solution of the Schockley-Ramo theorem, and its integration into the Geant4 application for tomographic emission (GATE) platform in order to perform accurately and, therefore, improve the simulations of pixellated detectors in different configurations with a simultaneous cathode and anode pixel readout. The model presented here is successfully validated against an existing detailed finite element simulator, the multi-geometry simulation code, with respect to the charge induced at the anode, taking into consideration interpixel charge sharing and crosstalk, and to the detector charge induction efficiency. As a final point, the model provides estimated energy spectra and time resolution for 57Co and 18F sources obtained with the GATE code after the incorporation of the proposed model.

  8. Development of a simplified simulation model for performance characterization of a pixellated CdZnTe multimodality imaging system.

    PubMed

    Guerra, P; Santos, A; Darambara, D G

    2008-02-21

    Current requirements of molecular imaging lead to the complete integration of complementary modalities in a single hybrid imaging system to correlate function and structure. Among the various existing detector technologies, which can be implemented to integrate nuclear modalities (PET and/or single-photon emission computed tomography with x-rays (CT) and most probably with MR, pixellated wide bandgap room temperature semiconductor detectors, such as CdZnTe and/or CdTe, are promising candidates. This paper deals with the development of a simplified simulation model for pixellated semiconductor radiation detectors, as a first step towards the performance characterization of a multimodality imaging system based on CdZnTe. In particular, this work presents a simple computational model, based on a 1D approximate solution of the Schockley-Ramo theorem, and its integration into the Geant4 application for tomographic emission (GATE) platform in order to perform accurately and, therefore, improve the simulations of pixellated detectors in different configurations with a simultaneous cathode and anode pixel readout. The model presented here is successfully validated against an existing detailed finite element simulator, the multi-geometry simulation code, with respect to the charge induced at the anode, taking into consideration interpixel charge sharing and crosstalk, and to the detector charge induction efficiency. As a final point, the model provides estimated energy spectra and time resolution for (57)Co and (18)F sources obtained with the GATE code after the incorporation of the proposed model. PMID:18263961

  9. A CdTe position sensitive detector for a hard X- and gamma-ray wide field camera

    SciTech Connect

    Caroli, E.; Cesare, G. de; Donati, A.; Dusi, W.; Landini, G.; Stephen, J.B.; Perotti, F.

    1998-12-31

    An important region of the electromagnetic spectrum for astrophysics is the hard X- and gamma ray band between 10 keV and a few MeV, where several processes occur in a wide variety of objects and with different spatial distribution and time scales. In order to fulfill the observational requirements in this energy range and taking into account the opportunities given by small/medium size missions (e.g., on the ISS), the authors have proposed a compact, wide field camera based on a thick (1 cm) position sensitive CdTe detector (PSD). The detector is made of an array of 128x96 CdTe microspectrometers with a pixel size of 2x2 mm{sup 2}. The basic element of the PSD is the linear module that is an independent detection unit with 32 CdTe crystals and monolithic front-electronics (ASIC) supported by a thin (300 {micro}m) ceramic layer. The expected performance of the PSD over the operative energy range and some of the required ASIC functionality are presented and discussed.

  10. Estimation of mammary gland composition using CdTe series detector developed for photon-counting mammography

    NASA Astrophysics Data System (ADS)

    Ihori, Akiko; Okamoto, Chizuru; Yamakawa, Tsutomu; Yamamoto, Shuichiro; Okada, Masahiro; Nakajima, Ai; Kato, Misa; Kodera, Yoshie

    2016-03-01

    Energy resolved photon-counting mammography is a new technology, which counts the number of photons that passes through an object, and presents it as a pixel value in an image of the object. Silicon semiconductor detectors are currently used in commercial mammography. However, the disadvantage of silicon is the low absorption efficiency for high X-ray energies. A cadmium telluride (CdTe) series detector has a high absorption efficiency over a wide energy range. In this study, we proposed a method to estimate the composition of the mammary gland using a CdTe series detector as a photon-counting detector. The fact that the detection rate of breast cancer in mammography is affected by mammary gland composition is now widely accepted. Assessment of composition of the mammary gland has important implications. An important advantage of our proposed technique is its ability to discriminate photons using three energy bins. We designed the CdTe series detector system using the MATLAB simulation software. The phantom contains nine regions with the ratio of glandular tissue and adipose varying in increments of 10%. The attenuation coefficient for each bin's energy was calculated from the number of input and output photons possessed by each. The evaluation results obtained by plotting the attenuation coefficient μ in a three-dimensional (3D) scatter plot show that the plots had a regular composition order congruent with that of the mammary gland. Consequently, we believe that our proposed method can be used to estimate the composition of the mammary gland.

  11. Discrimination between normal breast tissue and tumor tissue using CdTe series detector developed for photon-counting mammography

    NASA Astrophysics Data System (ADS)

    Okamoto, Chizuru; Ihori, Akiko; Yamakawa, Tsutomu; Yamamoto, Shuichiro; Okada, Masahiro; Kato, Misa; Nakajima, Ai; Kodera, Yoshie

    2016-03-01

    We propose a new mammography system using a cadmium telluride (CdTe) series photon-counting detector, having high absorption efficiency over a wide energy range. In a previous study, we showed that the use of high X-ray energy in digital mammography is useful from the viewpoint of exposure dose and image quality. In addition, the CdTe series detector can acquire X-ray spectrum information following transmission through a subject. This study focused on the tissue composition identified using spectral information obtained by a new photon-counting detector. Normal breast tissue consists entirely of adipose and glandular tissues. However, it is very difficult to find tumor tissue in the region of glandular tissue via a conventional mammogram, especially in dense breast because the attenuation coefficients of glandular tissue and tumor tissue are very close. As a fundamental examination, we considered a simulation phantom and showed the difference between normal breast tissue and tumor tissue of various thicknesses in a three-dimensional (3D) scatter plot. We were able to discriminate between both types of tissues. In addition, there was a tendency for the distribution to depend on the thickness of the tumor tissue. Thinner tumor tissues were shown to be closer in appearance to normal breast tissue. This study also demonstrated that the difference between these tissues could be made obvious by using a CdTe series detector. We believe that this differentiation is important, and therefore, expect this technology to be applied to new tumor detection systems in the future.

  12. Design of a high-resolution small-animal SPECT-CT system sharing a CdTe semiconductor detector

    NASA Astrophysics Data System (ADS)

    Ryu, Hyun-Ju; Lee, Young-Jin; Lee, Seung-Wan; Cho, Hyo-Min; Choi, Yu-Na; Kim, Hee-Joung

    2012-07-01

    A single photon emission computed tomography (SPECT) system with a co-registered X-y computed tomography (CT) system allows the convergence of functional information and morphologic information. The localization of radiopharmaceuticals on a SPECT can be enhanced by combining the SPECT with an anatomical modality, such as X-ray CT. Gamma-ray imaging for nuclear medicine devices and X-ray imaging systems for diagnostics has recently been developed based on semiconductor detectors, and semiconductor detector materials such as cadmium telluride (CdTe) or cadmium zinc telluride (CZT) are available for both X-ray and gamma-ray systems for small-animal imaging. CdTe or CZT detectors provide strong absorption and high detection efficiency of high energy X-ray and gamma-ray photons because of their large atomic numbers. In this study, a pinhole collimator SPECT system sharing a cadmium telluride (CdTe) detector with a CT was designed. The GEANT4 application for tomographic emission (GATE) v.6.1 was used for the simulation. The pinhole collimator was designed to obtain a high spatial resolution of the SPECT system. The acquisition time for each projection was 40 seconds, and 60 projections were obtained for tomographic image acquisition. The reconstruction was performed using ordered subset expectation maximization (OS-EM) algorithms. The sensitivity and the spatial resolution were measured on the GATE simulation to evaluate the system characteristics. The spatial resolution of the system calculated from the FWHM of Gaussian fitted PSF curve was 0.69 mm, and the sensitivity of the system was measured to be 0.354 cps/kBq by using a Tc-99m point source of 1 MBq for 800 seconds. A phantom study was performed to verify the design of the dual imaging modality system. The system will be built as designed, and it can be applied as a pre-clinical imaging system.

  13. Overcoming Zn segregation in CdZnTe with the temperature gradient annealing

    NASA Astrophysics Data System (ADS)

    Kim, K.; Bolotnikov, A. E.; Camarda, G. S.; Hossain, A.; James, R. B.

    2016-05-01

    The availability of large volume crystals with the same energy gap in melt-grown CdZnTe (CZT) is restricted due to the Zn segregation in CdTe hosts. We observed the migration of Zn in the solid phase along the positive temperature gradient direction both in situ and post-growth temperature gradient annealing (TGA) of CZT. Diffusivity of Zn obtained from the in situ TGA was approximately 10-5 cm2/s order and completely different mechanism with that of post-growth. The CZT ingots obtained through in situ TGA have uniform Zn and resistivity of 1010 Ω cm orders. The CZT detectors fabricated from in situ TGA applied ingots exhibit 10% of energy resolution for 59.5 keV peak of 241Am.

  14. RF sputtering deposition of CdTe on GaAs substrate

    NASA Astrophysics Data System (ADS)

    Adamiec, Krzysztof; Rutkowski, Jaroslaw; Bednarek, S.; Michalski, E.

    1997-06-01

    The fabrication of HgCdTe IR detectors demands high-quality CdTe or CdZnTe substrates. Bulk CdTe tends to twin, therefore large single crystals are generally not available. This problem could be circumvented by growing CdTe epilayers on an alternative large area substrate. Several studies have been made on the growth of CdTe on different substrates such as InSb, GaAs, Si and sapphire by MOCVD and MBE techniques. We report the initial results for the growth of CdTe buffer films on GaAs (100) substrates by sputter epitaxy. This crystal was chosen as the substrate material because of its transparency to IR radiation and availability as large area wafers with high structural perfection. Epitaxial films of CdTe were deposited in a sputtering system with a base pressure of 2 X 10-4 Pa. The GaAs substrate was degreased, etched in standard solution, and mounted immediately on a cooper substrate holder in the system. The substrates were ion etched in the sputtering system to remove surface oxide. The CdTe films were deposited in a wide substrate temperature range from 50 to 450 degrees C. Film thickness ranged from 0.1 to 5 micrometers , and deposition rates from 1 to 5 micrometers /h. The orientations and crystalline quality epitaxial films were characterized by x-ray diffraction. The surface morphology and the cross section of the gown CdTe layers were investigated by Nomarski interference contrast microscope. The optical and the electrical properties of the epitaxial films were investigated too. Structural characterization reveals that crystalline quality is a function of temperature of substrates. The single-crystals films grown at 300 degrees C on GaAs showed a best surface morphology.

  15. Evaluation of a Compton scattering camera using 3D position-sensitive CdZnTe detectors

    NASA Astrophysics Data System (ADS)

    Du, Yanfeng; He, Zhong; Knoll, Glenn F.; Wehe, David K.; Li, Weiqi

    1999-10-01

    A CZT Compton Camera (CCC) is being built using two 3D position sensitive CZT detectors. Expected system performance was analyzed by analytical and Monte Carlo approaches. Based on the measurement of detector energy and position resolution, the expected angular resolution is approximately 3 degree and approximately 2 degrees for a +/- 30 degrees FOV for 511 keV and 1 MeV (gamma) -rays, respectively. The intrinsic efficiency for a point source 10 cm from the first detector surface ranges from 1.5 X 10-4 to 8.8 X 10-6 for 500 keV to 3 MeV.

  16. Post-Growth Annealing of Bridgman-grown CdZnTe and CdMnTe Crystals for Room-temperature Nuclear Radiation Detectors

    DOE PAGES

    Egarievwe, Stephen U.; Yang, Ge; Egarievwe, Alexander; Okwechime, Ifechukwude O.; Gray, Justin; Hales, Zaveon M.; Hossain, Anwar; Camarda, Guiseppe S.; Bolotnikov, Aleksey E.; James, Ralph B.

    2015-02-11

    Bridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray- and gamma-ray-detectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510 °C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570 °C in Cd vapor for 26 h, whilst their electrical resistivity fell by an ordermore » of 102. During the temperature-gradient annealing of CMT at 730 °C and an 18 °C/cm temperature gradient for 18 h in a vacuum of 10-5 mbar, we observed the diffusion of Te from the sample, causing a reduction in size of the Te inclusions. For CZT samples annealed at 700 °C in a 10 °C/cm temperature gradient, we observed the migration of Te inclusions from a low-temperature region to a high one at 0.022 μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10-5 mbar at 570 °C and 30 °C/cm for 18 h, some Te inclusions moved toward the high-temperature side of the wafer, while other inclusions of the same size, i.e., 10 µm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT- and CMT-wafers are complex phenomena that depend on certain conditions.« less

  17. Post-Growth Annealing of Bridgman-grown CdZnTe and CdMnTe Crystals for Room-temperature Nuclear Radiation Detectors

    SciTech Connect

    Egarievwe, Stephen U.; Yang, Ge; Egarievwe, Alexander; Okwechime, Ifechukwude O.; Gray, Justin; Hales, Zaveon M.; Hossain, Anwar; Camarda, Guiseppe S.; Bolotnikov, Aleksey E.; James, Ralph B.

    2015-02-11

    Bridgman-grown cadmium zinc telluride (CdZnTe or CZT) and cadmium manganese telluride (CdMnTe or CMT) crystals often have Te inclusions that limit their performances as X-ray- and gamma-ray-detectors. We present here the results of post-growth thermal annealing aimed at reducing and eliminating Te inclusions in them. In a 2D analysis, we observed that the sizes of the Te inclusions declined to 92% during a 60-h annealing of CZT at 510 °C under Cd vapor. Further, tellurium inclusions were eliminated completely in CMT samples annealed at 570 °C in Cd vapor for 26 h, whilst their electrical resistivity fell by an order of 102. During the temperature-gradient annealing of CMT at 730 °C and an 18 °C/cm temperature gradient for 18 h in a vacuum of 10-5 mbar, we observed the diffusion of Te from the sample, causing a reduction in size of the Te inclusions. For CZT samples annealed at 700 °C in a 10 °C/cm temperature gradient, we observed the migration of Te inclusions from a low-temperature region to a high one at 0.022 μm/s. During the temperature-gradient annealing of CZT in a vacuum of 10-5 mbar at 570 °C and 30 °C/cm for 18 h, some Te inclusions moved toward the high-temperature side of the wafer, while other inclusions of the same size, i.e., 10 µm in diameter, remained in the same position. These results show that the migration, diffusion, and reaction of Te with Cd in the matrix of CZT- and CMT-wafers are complex phenomena that depend on certain conditions.

  18. Thin-film CdTe detector for microdosimetric study of radiation dose enhancement at gold-tissue interface.

    PubMed

    Paudel, Nava Raj; Shvydka, Diana; Parsai, E Ishmael

    2016-01-01

    Presence of interfaces between high and low atomic number (Z) materials, often encountered in diagnostic imaging and radiation therapy, leads to radiation dose perturbation. It is characterized by a very narrow region of sharp dose enhancement at the interface. A rapid falloff of dose enhancement over a very short distance from the interface makes the experimental dosimetry nontrivial. We use an in-house-built inexpensive thin-film Cadmium Telluride (CdTe) photodetector to study this effect at the gold-tissue interface and verify our experimental results with Monte Carlo (MC) modeling. Three-micron thick thin-film CdTe photodetectors were fabricated in our lab. One-, ten- or one hundred-micron thick gold foils placed in a tissue-equivalent-phantom were irradiated with a clinical Ir-192 high-dose-rate (HDR) source and current measured with a CdTe detector in each case was compared with the current measured for all uniform tissue-equivalent phantom. Percentage signal enhancement (PSE) due to each gold foil was then compared against MC modeled percentage dose enhancement (PDE), obtained from the geometry mimicking the experimental setup. The experimental PSEs due to 1, 10, and 100 μm thick gold foils at the closest measured distance of 12.5μm from the interface were 42.6 ± 10.8 , 137.0 ± 11.9, and 203.0 ± 15.4, respectively. The corresponding MC modeled PDEs were 38.1 ± 1, 164 ± 1, and 249 ± 1, respectively. The experimental and MC modeled values showed a closer agreement at the larger distances from the interface. The dose enhancement in the vicinity of gold-tissue interface was successfully measured using an in-house-built, high-resolution CdTe-based photodetector and validated with MC simulations. A close agreement between experimental and the MC modeled results shows that CdTe detector can be utilized for mapping interface dose distribution encountered in the application of ionizing radiation. PMID:27685139

  19. Novel Surface Preparation and Contacts for CdZnTe Nuclear Radiation Detectors Using Patterned Films of Semiconductors and Insulators

    NASA Astrophysics Data System (ADS)

    Burger, Arnold; Groza, Michael; Conway, Adam; Payne, Steve

    2013-04-01

    The semiconductor Cadmium Zinc Telluride (CZT) has emerged as the material of choice for room temperature detection of X-rays and gamma-rays. The detectors will cover the energy range from 30 keV to several MeV, and will achieve excellent 662 keV energy resolution. The development of high resolution gamma ray detectors based on CZT is dependent on low electronic noise levels. One common source of noise is the surface leakage current, which limits the performance of advanced readout schemes such as the coplanar grid and pixelated architectures with steering grids. Excessive bulk leakage current can result from one of several surface effects: leaky native oxides, unsatisfied bonds, and surface damage. We propose to fabricate and test oriented [111] CZT crystals with thicknesses up to 1.5 cm with an innovative detection technique based on co-planar or other electron only transport designs using plasma processing, thin film sputtering, chemical passivation and wet etching techniques. Compared to conventional pixel detectors, the proposed contact configuration needs lower power consumption and a lower cost. The detector design can be used for building very low-cost handheld radiation detection devices.

  20. Signal formation on a serpentine delay-line electrode patterned on the CdZnTe detector

    NASA Astrophysics Data System (ADS)

    Kim, Geehyun; Karbowski, Joseph; Hammig, Mark D.

    2011-10-01

    Delay-line electrodes can simplify the readout hardware and reduce the power requirements of a nuclear radiation detector by replacing dozens or hundreds of readout circuits with only one or two time-sensitive readouts per detector face. The simplified means of lateral position-sensing with micrometer-range resolution was previously validated upon high-resistivity silicon, with the ultimate goal of mapping the recoil electrons from gamma-ray events, thereby increasing the angular resolution of gamma-cameras. However, the effect of the induced current on non-collecting legs of the meander pattern was not evaluated, a deficiency addressed in this paper, in which a Cd 0.9Zn 0.1Te (CZT) bulk crystal was used as the substrate. We present simulations of: (1) the electric field distribution, as calculated with MAXWELL ® 12.0, within the CZT detector with the delay-line electrode, (2) the charge carrier drift motion within the semiconductor, and (3) the propagation of the induced charge signal along the meandering electrode pattern. CZT detectors purchased from ORBOTECH were reprocessed for studying various metal-semiconductor contacts, and with optimized interfaces, the fabrication of the delay-line electrode was performed using photolithographic processes in the Lurie Nanofabrication Facility in the University of Michigan. Current-voltage ( I- V) characteristic curves were obtained for performance evaluation and compared with pre-processing data. Readout circuits were connected to the fabricated CZT detector to test the lateral position-sensing, and the overlay design used to balance the transmission line electrode is discussed.

  1. OPTIMIZATION OF VIRTUAL FRISCH-GRID CdZnTe DETECTOR DESIGNS FOR IMAGING AND SPECTROSCOPY OF GAMMA RAYS.

    SciTech Connect

    BOLOTNIKOV,A.E.; ABDUL-JABBAR, N.M.; BABALOLA, S.; CAMARDA, G.S.; CUI, Y.; HOSSAIN, A.; JACKSON, E.; JACKSON, H.; JAMES, J.R.; LURYI, A.L.; JAMES, R.B.

    2007-08-21

    In the past, various virtual Frisch-grid designs have been proposed for cadmium zinc telluride (CZT) and other compound semiconductor detectors. These include three-terminal, semi-spherical, CAPture, Frisch-ring, capacitive Frisch-grid and pixel devices (along with their modifications). Among them, the Frisch-grid design employing a non-contacting ring extended over the entire side surfaces of parallelepiped-shaped CZT crystals is the most promising. The defect-free parallelepiped-shaped crystals with typical dimensions of 5x5{approx}12 mm3 are easy to produce and can be arranged into large arrays used for imaging and gamma-ray spectroscopy. In this paper, we report on further advances of the virtual Frisch-grid detector design for the parallelepiped-shaped CZT crystals. Both the experimental testing and modeling results are described.

  2. Effect of electron transport properties on unipolar CdZnTe radiation detectors: LUND, SpectrumPlus, and Coplanar Grid

    SciTech Connect

    Ralph B. James

    2000-01-07

    Device simulations of (1) the laterally-contacted-unipolar-nuclear detector (LUND), (2) the SpectrumPlus, (3) and the coplanar grid made of Cd{sub 0.9}Zn{sub 0.1}Te (CZT) were performed for {sup 137}Cs irradiation 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 materials for radiation detector applications. For the simulated unipolar devices, the active device volumes were relatively large and the energy 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 devices.

  3. Two CdZnTe Detector-Equipped Gamma-ray Spectrometers for Attribute Measurements on Irradiated Nuclear Fuel

    SciTech Connect

    Hartwell, John Kelvin; Winston, Philip Lon; Marts, Donna Jeanne; Moore-McAteer, Lisa Dawn; Taylor, Steven Cheney

    2003-04-01

    Some United States Department of Energy-owned spent fuel elements from foreign research reactors (FRRs) are presently being shipped from the reactor location to the US for storage at the Idaho National Engineering and Environmental Laboratory (INEEL). Two cadmium zinc telluride detector-based gamma-ray spectrometers have been developed to confirm the irradiation status of these fuels. One spectrometer is configured to operate underwater in the spent fuel pool of the shipping location, while the other is configured to interrogate elements on receipt in the dry transfer cell at the INEEL’s Interim Fuel Storage Facility (IFSF). Both units have been operationally tested at the INEEL.

  4. Comparing performances of a CdTe X-ray spectroscopic detector and an X-ray dual-energy sandwich detector

    NASA Astrophysics Data System (ADS)

    Gorecki, A.; Brambilla, A.; Moulin, V.; Gaborieau, E.; Radisson, P.; Verger, L.

    2013-11-01

    Multi-energy (ME) detectors are becoming a serious alternative to classical dual-energy sandwich (DE-S) detectors for X-ray applications such as medical imaging or explosive detection. They can use the full X-ray spectrum of irradiated materials, rather than disposing only of low and high energy measurements, which may be mixed. In this article, we intend to compare both simulated and real industrial detection systems, operating at a high count rate, independently of the dimensions of the measurements and independently of any signal processing methods. Simulations or prototypes of similar detectors have already been compared (see [1] for instance), but never independently of estimation methods and never with real detectors. We have simulated both an ME detector made of CdTe - based on the characteristics of the MultiX ME100 and - a DE-S detector - based on the characteristics of the Detection Technology's X-Card 1.5-64DE model. These detectors were compared to a perfect spectroscopic detector and an optimal DE-S detector. For comparison purposes, two approaches were investigated. The first approach addresses how to distinguise signals, while the second relates to identifying materials. Performance criteria were defined and comparisons were made over a range of material thicknesses and with different photon statistics. Experimental measurements in a specific configuration were acquired to checks simulations. Results showed good agreement between the ME simulation and the ME100 detector. Both criteria seem to be equivalent, and the ME detector performs 3.5 times better than the DE-S detector with same photon statistics based on simulations and experimental measurements. Regardless of the photon statistics ME detectors appeared more efficient than DE-S detectors for all material thicknesses between 1 and 9 cm when measuring plastics with an attenuation signature close that of explosive materials. This translates into an improved false detection rate (FDR): DE

  5. Characterization of polarization phenomenon in Al-Schottky CdTe detectors using a spectroscopic analysis method

    NASA Astrophysics Data System (ADS)

    Meuris, Aline; Limousin, Olivier; Blondel, Claire

    2011-10-01

    CdTe radiation detectors equipped with Schottky contacts are known to show spectral response degradation over time under biasing. Nevertheless, they can be used as high-resolution spectrometers for X-rays and gamma-rays with moderate cooling and high voltage. Spectroscopic long-term measurements have been performed with Al/CdTe/Pt pixel detectors of 0.5, 1 and 2 mm thicknesses and 241Am source from -13 to +16 °C to evaluate how long they can be operated. Experimental results are confronted to simulations using the charge accumulation model for electric field. Activation energy for collection efficiency stability and peak shift was measured at 1.0-1.2 eV although deep acceptor levels responsible for hole detrapping during polarization were evaluated by other methods at EV +0.6-0.8 eV. The difference is probably due to a thermal effect of pre-polarization before biasing the detector.

  6. An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras

    DOE PAGES

    Bolotnikov, A. E.; Ackley, K.; Camarda, G. S.; Cherches, C.; Cui, Y.; De Geronimo, G.; Fried, J.; Hodges, D.; Hossain, A.; Lee, W.; et al

    2015-07-28

    We developed a robust and low-cost array of virtual Frisch-grid CdZnTe (CZT) detectors coupled to a front-end readout ASIC for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6x6x15 mm3 detectors grouped into 3x3 sub-arrays of 2x2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics.more » The further enhancement of the arrays’ performance and reduction of their cost are made possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.« less

  7. An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras

    SciTech Connect

    Bolotnikov, A. E.; Ackley, K.; Camarda, G. S.; Cherches, C.; Cui, Y.; De Geronimo, G.; Fried, J.; Hodges, D.; Hossain, A.; Lee, W.; Mahler, G.; Maritato, M.; Petryk, M.; Roy, U.; Salwen, C.; Vernon, E.; Yang, G.; James, R. B.

    2015-07-28

    We developed a robust and low-cost array of virtual Frisch-grid CdZnTe (CZT) detectors coupled to a front-end readout ASIC for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6x6x15 mm3 detectors grouped into 3x3 sub-arrays of 2x2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays’ performance and reduction of their cost are made possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.

  8. An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras

    SciTech Connect

    Bolotnikov, A. E. Ackley, K.; Camarda, G. S.; Cherches, C.; Cui, Y.; De Geronimo, G.; Fried, J.; Hossain, A.; Mahler, G.; Maritato, M.; Roy, U.; Salwen, C.; Vernon, E.; Yang, G.; James, R. B.; Hodges, D.; Lee, W.; Petryk, M.

    2015-07-15

    We developed a robust and low-cost array of virtual Frisch-grid CdZnTe detectors coupled to a front-end readout application-specific integrated circuit (ASIC) for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6 × 6 × 15 mm{sup 3} detectors grouped into 3 × 3 sub-arrays of 2 × 2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays’ performance and reduction of their cost are possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.

  9. An array of virtual Frisch-grid CdZnTe detectors and a front-end application-specific integrated circuit for large-area position-sensitive gamma-ray cameras.

    PubMed

    Bolotnikov, A E; Ackley, K; Camarda, G S; Cherches, C; Cui, Y; De Geronimo, G; Fried, J; Hodges, D; Hossain, A; Lee, W; Mahler, G; Maritato, M; Petryk, M; Roy, U; Salwen, C; Vernon, E; Yang, G; James, R B

    2015-07-01

    We developed a robust and low-cost array of virtual Frisch-grid CdZnTe detectors coupled to a front-end readout application-specific integrated circuit (ASIC) for spectroscopy and imaging of gamma rays. The array operates as a self-reliant detector module. It is comprised of 36 close-packed 6 × 6 × 15 mm(3) detectors grouped into 3 × 3 sub-arrays of 2 × 2 detectors with the common cathodes. The front-end analog ASIC accommodates up to 36 anode and 9 cathode inputs. Several detector modules can be integrated into a single- or multi-layer unit operating as a Compton or a coded-aperture camera. We present the results from testing two fully assembled modules and readout electronics. The further enhancement of the arrays' performance and reduction of their cost are possible by using position-sensitive virtual Frisch-grid detectors, which allow for accurate corrections of the response of material non-uniformities caused by crystal defects.

  10. Fine-pitch CdTe detector for hard X-ray imaging and spectroscopy of the Sun with the FOXSI rocket experiment

    NASA Astrophysics Data System (ADS)

    Ishikawa, Shin-nosuke; Katsuragawa, Miho; Watanabe, Shin; Uchida, Yuusuke; Takeda, Shin'ichiro; Takahashi, Tadayuki; Saito, Shinya; Glesener, Lindsay; Buitrago-Casas, Juan Camilo; Krucker, Säm.; Christe, Steven

    2016-07-01

    We have developed a fine-pitch hard X-ray (HXR) detector using a cadmium telluride (CdTe) semiconductor for imaging and spectroscopy for the second launch of the Focusing Optics Solar X-ray Imager (FOXSI). FOXSI is a rocket experiment to perform high sensitivity HXR observations from 4 to 15 keV using the new technique of HXR focusing optics. The focal plane detector requires <100μm position resolution (to take advantage of the angular resolution of the optics) and ≈1 keV energy resolution (full width at half maximum (FWHM)) for spectroscopy down to 4 keV, with moderate cooling (>-30°C). Double-sided silicon strip detectors were used for the first FOXSI flight in 2012 to meet these criteria. To improve the detectors' efficiency (66% at 15 keV for the silicon detectors) and position resolution of 75 μm for the second launch, we fabricated double-sided CdTe strip detectors with a position resolution of 60 μm and almost 100% efficiency for the FOXSI energy range. The sensitive area is 7.67 mm × 7.67 mm, corresponding to the field of view of 791'' × 791''. An energy resolution of 1 keV (FWHM) and low-energy threshold of ≈4 keV were achieved in laboratory calibrations. The second launch of FOXSI was performed on 11 December 2014, and images from the Sun were successfully obtained with the CdTe detector. Therefore, we successfully demonstrated the detector concept and the usefulness of this technique for future HXR observations of the Sun.

  11. Digital performance improvements of a CdTe pixel detector for high flux energy-resolved X-ray imaging

    NASA Astrophysics Data System (ADS)

    Abbene, L.; Gerardi, G.; Principato, F.

    2015-03-01

    Photon counting detectors with energy resolving capabilities are desired for high flux X-ray imaging. In this work, we present the performance of a pixelated Schottky Al/p-CdTe/Pt detector (4×4) coupled to a custom-designed digital readout electronics for high flux measurements. The detector (4×4×2 mm3) has an anode layout based on an array of 16 pixels with a geometric pitch of 1 mm (pixel size of 0.6 mm). The 4-channel readout electronics is able to continuously digitize and process the signals from each pixel, performing multi-parameter analysis (event arrival time, pulse shape, pulse height, pulse time width, etc.) even at high fluxes and at different throughput and energy resolution conditions. The spectroscopic response of the system to monochromatic X-ray sources, at both low and high rates, is presented with particular attention to the mitigation of some typical spectral distortions (pile-up, baseline shifts and charge sharing). At a photon counting rate of 520 kcps/pixel, the system exhibits an energy resolution (FWHM at 59.5 keV) of 4.6%, 7.1% and 9% at throughputs of 0.9%, 16% and 82%, respectively. Measurements of Ag-target X-ray spectra also show the ability of the system to perform accurate estimation of the input counting rate up to 1.1 Mcps/pixel. The aim of this work is to point out, beside the appealing properties of CdTe detectors, the benefits of the digital approach in the development of high-performance energy resolved photon counting (ERPC) systems for high flux X-ray imaging.

  12. A 2D 4×4 Channel Readout ASIC for Pixelated CdTe Detectors for Medical Imaging Applications

    PubMed Central

    Macias-Montero, Jose-Gabriel; Sarraj, Maher; Chmeissani, Mokhtar; Martínez, Ricardo; Puigdengoles, Carles

    2015-01-01

    We present a 16-channel readout integrated circuit (ROIC) with nanosecond-resolution time to digital converter (TDC) for pixelated Cadmium Telluride (CdTe) gamma-ray detectors. The 4 × 4 pixel array ROIC is the proof of concept of the 10 × 10 pixel array readout ASIC for positron-emission tomography (PET) scanner, positron-emission mammography (PEM) scanner, and Compton gamma camera. The electronics of each individual pixel integrates an analog front-end with switchable gain, an analog to digital converter (ADC), configuration registers, and a 4-state digital controller. For every detected photon, the pixel electronics provides the energy deposited in the detector with 10-bit resolution, and a fast trigger signal for time stamp. The ASIC contains the 16-pixel matrix electronics, a digital controller, five global voltage references, a TDC, a temperature sensor, and a band-gap based current reference. The ASIC has been fabricated with TSMC 0.25 μm mixed-signal CMOS technology and occupies an area of 5.3 mm × 6.8 mm. The TDC shows a resolution of 95.5 ps, a precision of 600 ps at full width half maximum (FWHM), and a power consumption of 130 μW. In acquisition mode, the total power consumption of every pixel is 200 μW. An equivalent noise charge (ENC) of 160 e−RMS at maximum gain and negative polarity conditions has been measured at room temperature. PMID:26744545

  13. Photon counting X-ray imaging with CdTe pixel detectors based on XPAD2 circuit

    NASA Astrophysics Data System (ADS)

    Franchi, Romain; Glasser, Francis; Gasse, Adrien; Clemens, Jean-Claude

    2006-07-01

    A semiconductor hybrid pixel detector for photon counting X-ray imaging has been developed and tested under radiation. The sensor is based on recent uniform CdTe single crystal associated with XPAD 2 counting chip via innovative processes of interconnection. The building detector is 1 mm thick, with an area of 1 cm 2 and consists of 600 square pixels cells 330 μm side. The readout chip working in electron collection mode is capable of setting homogeneous threshold with only a dispersion of 730 e -. Maximum noise level has been evaluated around 15 keV. First experiments under X-rays demonstrate a very good efficiency of detection. Moreover, imaging system allows excellent linearity over a large-scale achieving count rate of 3×10 6 photons/s/mm 2. Spectrometric measurements point up the system potential in multi-energies applications by locating and resolving X-rays lines of 241Am and 57Co sources.

  14. Simulation of the Expected Performance of a Seamless Scanner for Brain PET Based on Highly Pixelated CdTe Detectors

    PubMed Central

    Mikhaylova, Ekaterina; De Lorenzo, Gianluca; Chmeissani, Mokhtar; Kolstein, Machiel; Cañadas, Mario; Arce, Pedro; Calderón, Yonatan; Uzun, Dilber; Ariño, Gerard; Macias-Montero, José Gabriel; Martinez, Ricardo; Puigdengoles, Carles; Cabruja, Enric

    2014-01-01

    The aim of this work is the evaluation of the design for a nonconventional PET scanner, the voxel imaging PET (VIP), based on pixelated room-temperature CdTe detectors yielding a true 3-D impact point with a density of 450 channels cm3, for a total 6 336 000 channels in a seamless ring shaped volume. The system is simulated and evaluated following the prescriptions of the NEMA NU 2-2001 and the NEMA NU 4-2008 standards. Results show that the excellent energy resolution of the CdTe detectors (1.6% for 511 keV photons), together with the small voxel pitch (1×1×2 mm3), and the crack-free ring geometry, give the design the potential to overcome the current limitations of PET scanners and to approach the intrinsic image resolution limits set by physics. The VIP is expected to reach a competitive sensitivity and a superior signal purity with respect to values commonly quoted for state-of-the-art scintillating crystal PETs. The system can provide 14 cps/kBq with a scatter fraction of 3.95% and 21 cps/kBq with a scatter fraction of 0.73% according to NEMA NU 2-2001 and NEMA NU 4-2008, respectively. The calculated NEC curve has a peak value of 122 kcps at 5.3 kBq/mL for NEMA NU 2-2001 and 908 kcps at 1.6 MBq/mL for NEMA NU 4-2008. The proposed scanner can achieve an image resolution of ~ 1 mm full-width at half-maximum in all directions. The virtually noise-free data sample leads to direct positive impact on the quality of the reconstructed images. As a consequence, high-quality high-resolution images can be obtained with significantly lower number of events compared to conventional scanners. Overall, simulation results suggest the VIP scanner can be operated either at normal dose for fast scanning and high patient throughput, or at low dose to decrease the patient radioactivity exposure. The design evaluation presented in this work is driving the development and the optimization of a fully operative prototype to prove the feasibility of the VIP concept. PMID:24108750

  15. High-rate x-ray spectroscopy in mammography with a CdTe detector: A digital pulse processing approach

    SciTech Connect

    Abbene, L.; Gerardi, G.; Principato, F.; Del Sordo, S.; Ienzi, R.; Raso, G.

    2010-12-15

    Purpose:Direct measurement of mammographic x-ray spectra under clinical conditions is a difficult task due to the high fluence rate of the x-ray beams as well as the limits in the development of high resolution detection systems in a high counting rate environment. In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate x-ray spectroscopy in mammography. Methods: The DPP system performs a digital pile-up inspection and a digital pulse height analysis of the detector signals, digitized through a 14-bit, 100 MHz digitizer, for x-ray spectroscopy even at high photon counting rates. We investigated on the response of the digital detection system both at low (150 cps) and at high photon counting rates (up to 500 kcps) by using monoenergetic x-ray sources and a nonclinical molybdenum anode x-ray tube. Clinical molybdenum x-ray spectrum measurements were also performed by using a pinhole collimator and a custom alignment device. Results: The detection system shows excellent performance up to 512 kcps with an energy resolution of 4.08% FWHM at 22.1 keV. Despite the high photon counting rate (up to 453 kcps), the molybdenum x-ray spectra, measured under clinical conditions, are characterized by a low number of pile-up events. The agreement between the attenuation curves and the half value layer values, obtained from the measured spectra, simulated spectra, and from the exposure values directly measured with an ionization chamber, also shows the accuracy of the measurements. Conclusions: These results make the proposed detection system a very attractive tool for both laboratory research and advanced quality controls in mammography.

  16. Research on uncooled CdTe gamma detectors as substitutes for ultrapure Ge. Final report 1 Aug 77-31 Jan 80

    SciTech Connect

    Lis, S.A.; Serreze, H.B.; Rusinek, H.; Reich, T.; Youdin, M.

    1980-06-01

    The physics and chemistry of cadmium telluride (CdTe) crystal growth and detector structures were investigated to provide the technological basis for reproducible fabrication of these devices. These gamma ray detectors can provide a unique combination of energy resolution, sensitivity, compactness, and economy (all with room temperature operation)--factors of prime importance for modern nuclear instrumentation. Topics investigated include the THM crystal growth process, mechanisms of metal-semiconductor and metal-electrolyte-semiconductor contact behavior, polarization phenomena, and advanced PIN device structures. Detectors developed under this program were examined for potential use in cerebral blood flow monitors. They were found to possess a number of features which make them appear attractive as substitutes for cryogenically cooled high purity germanium detectors.

  17. CdZnTe photodiode arrays for medical imaging

    SciTech Connect

    Sudharsanan, R.; Parodos, T.; Karam, N.H.; Ruzin, A.; Nemirovsky, Y.

    1996-08-01

    In this paper, we report on the design, fabrication, and performance of the first CdZnTe Schottky photodiode arrays for radiation detection. High pressure Bridgman-grown CdZnTe substrates with bulk resistivities in the range 10{sup 8} to 10{sup 10} ohm-cm were used. CdZnTe Schottky photodiodes were formed with In and Ti/Au contacts. Diode arrays with pixel sizes from 1000 x 1000 {mu}m to 100 x 100 {mu}m were fabricated. The diode`s I-V characteristics exhibited low leakage current and high bulk resistivity; leakage current decreased as diode pixel size was reduced. Response of these detector arrays to high energy photons was uniform and their energy resolution improved with smaller pixel size. 14 refs., 9 figs.

  18. Gamma ray detector modules

    NASA Technical Reports Server (NTRS)

    Capote, M. Albert (Inventor); Lenos, Howard A. (Inventor)

    2009-01-01

    A radiation detector assembly has a semiconductor detector array substrate of CdZnTe or CdTe, having a plurality of detector cell pads on a first surface thereof, the pads having a contact metallization and a solder barrier metallization. An interposer card has planar dimensions no larger than planar dimensions of the semiconductor detector array substrate, a plurality of interconnect pads on a first surface thereof, at least one readout semiconductor chip and at least one connector on a second surface thereof, each having planar dimensions no larger than the planar dimensions of the interposer card. Solder columns extend from contacts on the interposer first surface to the plurality of pads on the semiconductor detector array substrate first surface, the solder columns having at least one solder having a melting point or liquidus less than 120 degrees C. An encapsulant is disposed between the interposer circuit card first surface and the semiconductor detector array substrate first surface, encapsulating the solder columns, the encapsulant curing at a temperature no greater than 120 degrees C.

  19. Fast photoconductor CdTe detectors for synchrotron x-ray studies

    SciTech Connect

    Yoo, Sung Shik; Faurie, J.P.; Wang, Kemei; Montano, P.A. |; Huang Qiang; Rodricks, B.

    1993-09-01

    The Advanced Photon Source will be that brightest source of synchrotron x-rays when it becomes operational in 1996. During normal operation, the ring will be filled with 20 bunches of positrons with an interbunch spacing of 177 ns and a bunch width of 119 ps. To perform experiments with x-rays generated by positrons on these time scales one needs extremely high speed detectors. To achieve the necessary high speed, we are developing MBE-grown CdTe-base photoconductive position sensitive array detectors. The arrays fabricated have 64 pixels with a gap of 100 {mu}m between pixels. The high speed response of the devices was tested using a short pulse laser. X-ray static measurements were performed using an x-ray tube and synchrotron radiation to study the device`s response to flux and wavelength changes. This paper presents the response of the devices to some of these tests and discusses different physics aspects to be considered when designing high speed detectors.

  20. ILLUMINATION RESPONSE OF CDZNTE

    SciTech Connect

    Teague, L.; Washington, A.; Duff, M.

    2011-08-02

    CdZnTe (CZT) semiconducting crystals are of interest for use as room temperature X- and {gamma}-ray spectrometers. Several studies have focused on understanding the various electronic properties of these materials, such as the surface and bulk resistivities and the distribution of the electric field within the crystal. Specifically of interest is how these properties are influenced by a variety of factors including structural heterogeneities, such as secondary phases (SPs) and line defects as well as environmental effects. Herein, we report the bulk current, surface current, electric field distribution and performance of a spectrometer-grade CZT crystal exposed to above band-gap energy illumination.

  1. Effect of chemical etching on the surface roughness of CdZnTe and CdMnTe gamma radiation detectors

    SciTech Connect

    Hossain,A.; Babalola, S.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Yang, G.; Guo, M.; Kochanowska, D.; Mycielski, A.; Burger, A.; James, R.B.

    2008-08-11

    Generally, mechanical polishing is performed to diminish the cutting damage followed by chemical etching to remove the remaining damage on crystal surfaces. In this paper, we detail the findings from our study of the effects of various chemical treatments on the roughness of crystal surfaces. We prepared several CdZnTe (CZT) and CdMnTe (CMT) crystals by mechanical polishing with 5 {micro}m and/or lower grits of Al{sub 2}O{sub 3} abrasive papers including final polishing with 0.05-{micro}m particle size alumina powder and then etched them for different periods with a 2%, 5% Bromine-Methanol (B-M) solution, and also with an E-solution (HNO{sub 3}:H{sub 2}O:Cr{sub 2}O{sub 7}). The material removal rate (etching rate) from the crystals was found to be 10 {micro}m, 30 {micro}m, and 15 {micro}m per minute, respectively. The roughness of the resulting surfaces was determined by the Atomic Force Microscopy (AFM) to identify the most efficient surface processing method by combining mechanical and chemical polishing.

  2. Point Defect Characterization in CdZnTe

    SciTech Connect

    Gul,R.; Li, Z.; Bolotnikov, A.; Keeter, K.; Rodriguez, R.; James, R.

    2009-03-24

    Measurements of the defect levels and performance testing of CdZnTe detectors were performed by means of Current Deep Level Transient Spectroscopy (I-DLTS), Transient Charge Technique (TCT), Current versus Voltage measurements (I-V), and gamma-ray spectroscopy. CdZnTe crystals were acquired from different commercial vendors and characterized for their point defects. I-DLTS studies included measurements of defect parameters such as energy levels in the band gap, carrier capture cross sections, and defect densities. The induced current due to laser-generated carriers was measured using TCT. The data were used to determine the transport properties of the detectors under study. A good correlation was found between the point defects in the detectors and their performance.

  3. CdZnTe Background Measurements at Balloon Altitudes with PoRTIA

    NASA Technical Reports Server (NTRS)

    Parsons, A.; Barthelmy, S.; Bartlett, L.; Gehrels, N.; Naya, J.; Stahle, C. M.; Tueller, J.; Teegarden, B.

    2003-01-01

    Measurements of the CdZnTe internal background at balloon altitudes are essential to determine which physical processes make the most important background contributions. We present results from CdZnTe background measurements made by PoRTIA, a small CdZnTe balloon instrument that was flown three times in three different shielding configurations. PoRTIA was passively shielded during its first flight from Palestine, Texas and actively shielded as a piggyback instrument on the GRIS balloon experiment during its second and third flights from Alice Springs, Australia, using the thick GRIS Nal anticoincidence shield. A significant CdZnTe background reduction was achieved during the third flight with PoRTIA placed completely inside the GRIS shield and blocking crystal, and thus completely surrounded by 15 cm of Nal. A unique balloon altitude background data set is provided by CdZnTe and Ge detectors simultaneously surrounded by the same thick anticoincidence shield; the presence of a single coxial Ge detector inside the shield next to PoRTIA allowed a measurement of the ambient neutron flux inside the shield throughout the flight. These neutrons interact with the detector material to produce isomeric states of the Cd, Zn and Te nuclei that radiatively decay; calculations are presented that indicate that these decays may explain most of the fully shielded CdZnTe background.

  4. Dynamic X-ray direct conversion detector using a CdTe polycrystalline layer coupled to a CMOS readout chip

    NASA Astrophysics Data System (ADS)

    Arques, Marc; Renet, Sébastien; Brambilla, Andréa; Feuillet, Guy; Gasse, Adrien; Billon-Pierron, Nicolas; Jolliot, Muriel; Mathieu, Lydie; Rohr, Pierre

    2011-05-01

    A direct detection X-ray imager is presented. It uses polycrystalline cadmium telluride (CdTe) grown by close space sublimation technique for the X-ray photoconductor. A 15 mm×15 mm CdTe layer is connected to a 200×200 pixel readout CMOS by indium bumping. X-ray performance at 16 frames/s rate is measured. In particular a readout noise of 0.5 X-ray, an MTF of 50% at 4 lp/mm and a DQE of 20% at 4 lp/mm are obtained.

  5. Determination of 235U enrichment with a large volume CZT detector

    NASA Astrophysics Data System (ADS)

    Mortreau, Patricia; Berndt, Reinhard

    2006-01-01

    Room-temperature CdZnTe and CdTe detectors have been routinely used in the field of Nuclear Safeguards for many years [Ivanov et al., Development of large volume hemispheric CdZnTe detectors for use in safeguards applications, ESARDA European Safeguards Research and Development Association, Le Corum, Montpellier, France, 1997, p. 447; Czock and Arlt, Nucl. Instr. and Meth. A 458 (2001) 175; Arlt et al., Nucl. Instr. and Meth. A 428 (1999) 127; Lebrun et al., Nucl. Instr. and Meth. A 448 (2000) 598; Aparo et al., Development and implementation of compact gamma spectrometers for spent fuel measurements, in: Proceedings, 21st Annual ESARDA, 1999; Arlt and Rudsquist, Nucl. Instr. and Meth. A 380 (1996) 455; Khusainov et al., High resolution pin type CdTe detectors for the verification of nuclear material, in: Proceedings, 17th Annual ESARDA European Safeguards Research and Development Association, 1995; Mortreau and Berndt, Nucl. Instr. and Meth. A 458 (2001) 183; Ruhter et al., UCRL-JC-130548, 1998; Abbas et al., Nucl. Instr. and Meth. A 405 (1998) 153; Ruhter and Gunnink, Nucl. Instr. and Meth. A 353 (1994) 716]. Due to their performance and small size, they are ideal detectors for hand-held applications such as verification of spent and fresh fuel, U/Pu attribute tests as well as for the determination of 235U enrichment. The hemispherical CdZnTe type produced by RITEC (Riga, Latvia) [Ivanov et al., 1997] is the most widely used detector in the field of inspection. With volumes ranging from 2 to 1500 mm 3, their spectral performance is such that the use of electronic processing to correct the pulse shape is not required. This paper reports on the work carried out with a large volume (15×15×7.5 mm 3) and high efficiency hemispherical CdZnTe detector for the determination of 235U enrichment. The measurements were made with certified uranium samples whose enrichment ranging from 0.31% to 92.42%, cover the whole range of in-field measurement conditions. The interposed

  6. CdZnTe solid-state gamma cameras

    SciTech Connect

    Butler, J.F.; Lingren, C.L.; Friesenhahn, S.J.

    1998-06-01

    The authors report the development of a CdZnTe gamma ray imager whose advantages over the conventional Anger camera include (1) improved contrast resulting from superior energy resolution and unambiguous position determination and (2) the small size and weight and high reliability inherent in an all-solid-state construction. It provides high energy resolution and peak efficiency by incorporating Digirad`s new SpectrumPlus{trademark} detector technology. The new imager employs a modular design, in which each 1 inch x 1 inch module incorporates a monolithic 64-element CdZnTe detector array and ASIC-based circuitry that provides signal conditioning for every channel, identification of valid events and addressing functions. Imagers with a wide range of sizes and shapes can be assembled by tiling modules together on a specially designed signal routing board.

  7. Hard X-ray polarimetry with Caliste, a high performance CdTe based imaging spectrometer

    NASA Astrophysics Data System (ADS)

    Antier, S.; Ferrando, P.; Limousin, O.; Caroli, E.; Curado da Silva, R. M.; Blondel, C.; Chipaux, R.; Honkimaki, V.; Horeau, B.; Laurent, P.; Maia, J. M.; Meuris, A.; Del Sordo, S.; Stephen, J. B.

    2015-06-01

    Since the initial exploration of the X- and soft γ-ray sky in the 60's, high-energy celestial sources have been mainly characterized through imaging, spectroscopy and timing analysis. Despite tremendous progress in the field, the radiation mechanisms at work in sources such as neutrons stars, black holes, and Active Galactic Nuclei are still unclear. The polarization state of the radiation is an observational parameter which brings key additional information about the physical processes in these high energy sources, allowing the discrimination between competing models which may otherwise all be consistent with other types of measurement. This is why most of the projects for the next generation of space missions covering the few tens of keV to the MeV region require a polarization measurement capability. A key element enabling this capability, in this energy range, is a detector system allowing the identification and characterization of Compton interactions as they are the main process at play. The compact hard X-ray imaging spectrometer module, developed in CEA with the generic name of "Caliste" module, is such a detector. In this paper, we present experimental results for two types of Caliste-256 modules, one based on a CdTe crystal, the other one on a CdZnTe crystal, which have been exposed to linearly polarized beams at the European Synchrotron Radiation Facility (ESRF). These results, obtained at 200 and 300 keV, demonstrate the capability of these modules to detect Compton events and to give an accurate determination of the polarization parameters (polarization angle and fraction) of the incoming beam. For example, applying an optimized selection to our data set, equivalent to select 90° Compton scattered interactions in the detector plane, we find a modulation factor Q of 0.78 ± 0.06 in the 200-300 keV range. The polarization angle and fraction are derived with accuracies of approximately 1° and 5 % respectively for both CdZnTe and CdTe crystals. The

  8. Semiconductor P-I-N detector

    DOEpatents

    Sudharsanan, Rengarajan; Karam, Nasser H.

    2001-01-01

    A semiconductor P-I-N detector including an intrinsic wafer, a P-doped layer, an N-doped layer, and a boundary layer for reducing the diffusion of dopants into the intrinsic wafer. The boundary layer is positioned between one of the doped regions and the intrinsic wafer. The intrinsic wafer can be composed of CdZnTe or CdTe, the P-doped layer can be composed of ZnTe doped with copper, and the N-doped layer can be composed of CdS doped with indium. The boundary layers is formed of an undoped semiconductor material. The boundary layer can be deposited onto the underlying intrinsic wafer. The doped regions are then typically formed by a deposition process or by doping a section of the deposited boundary layer.

  9. Analytical bond-order potential for the Cd-Zn-Te ternary system

    NASA Astrophysics Data System (ADS)

    Ward, D. K.; Zhou, X. W.; Wong, B. M.; Doty, F. P.; Zimmerman, J. A.

    2012-12-01

    Cd-Zn-Te ternary alloyed semiconductor compounds are key materials in radiation detection and photovoltaic applications. Currently, crystalline defects such as dislocations limit the performance of these materials. Atomistic simulations are a powerful method for exploring crystalline defects at a resolution unattainable by experimental techniques. To enable accurate atomistic simulations of defects in the Cd-Zn-Te systems, we develop a full Cd-Zn-Te ternary bond-order potential. This Cd-Zn-Te potential has numerous unique advantages over other potential formulations: (1) It is analytically derived from quantum mechanical theories and is therefore more likely to be transferable to environments that are not explicitly tested. (2) A variety of elemental and compound configurations (with coordination varying from 1 to 12) including small clusters, bulk lattices, defects, and surfaces are explicitly considered during parameterization. As a result, the potential captures structural and property trends close to those seen in experiments and quantum mechanical calculations and provides a good description of melting temperature, defect characteristics, and surface reconstructions. (3) Most importantly, this potential is validated to correctly predict the crystalline growth of the ground-state structures for Cd, Zn, Te elements as well as CdTe, ZnTe, and Cd1-xZnxTe compounds during highly challenging molecular dynamics vapor deposition simulations.

  10. Toward VIP-PIX: A Low Noise Readout ASIC for Pixelated CdTe Gamma-Ray Detectors for Use in the Next Generation of PET Scanners

    PubMed Central

    Macias-Montero, Jose-Gabriel; Sarraj, Maher; Chmeissani, Mokhtar; Puigdengoles, Carles; Lorenzo, Gianluca De; Martínez, Ricardo

    2013-01-01

    VIP-PIX will be a low noise and low power pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) detectors. The proposed pixel will be part of a 2D pixel-array detector for various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. Each pixel will include a SAR ADC that provides the energy deposited with 10-bit resolution. Simultaneously, the self-triggered pixel which will be connected to a global time-to-digital converter (TDC) with 1 ns resolution will provide the event’s time stamp. The analog part of the readout chain and the ADC have been fabricated with TSMC 0.25 μm mixed-signal CMOS technology and characterized with an external test pulse. The power consumption of these parts is 200 μW from a 2.5 V supply. It offers 4 switchable gains from ±10 mV/fC to ±40 mV/fC and an input charge dynamic range of up to ±70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 e− RMS at room temperature. PMID:24187382

  11. Toward VIP-PIX: A Low Noise Readout ASIC for Pixelated CdTe Gamma-Ray Detectors for Use in the Next Generation of PET Scanners.

    PubMed

    Macias-Montero, Jose-Gabriel; Sarraj, Maher; Chmeissani, Mokhtar; Puigdengoles, Carles; Lorenzo, Gianluca De; Martínez, Ricardo

    2013-08-01

    VIP-PIX will be a low noise and low power pixel readout electronics with digital output for pixelated Cadmium Telluride (CdTe) detectors. The proposed pixel will be part of a 2D pixel-array detector for various types of nuclear medicine imaging devices such as positron-emission tomography (PET) scanners, Compton gamma cameras, and positron-emission mammography (PEM) scanners. Each pixel will include a SAR ADC that provides the energy deposited with 10-bit resolution. Simultaneously, the self-triggered pixel which will be connected to a global time-to-digital converter (TDC) with 1 ns resolution will provide the event's time stamp. The analog part of the readout chain and the ADC have been fabricated with TSMC 0.25 μm mixed-signal CMOS technology and characterized with an external test pulse. The power consumption of these parts is 200 μW from a 2.5 V supply. It offers 4 switchable gains from ±10 mV/fC to ±40 mV/fC and an input charge dynamic range of up to ±70 fC for the minimum gain for both polarities. Based on noise measurements, the expected equivalent noise charge (ENC) is 65 e(-) RMS at room temperature.

  12. Investigation of CdZnTe for Thin-Film Tandem Solar Cell Applications: Preprint

    SciTech Connect

    Dhere, R.; Gessert, T.; Zhou, J.; Asher, S.; Pankow, J.; Moutinho, H.

    2003-04-01

    Modeling of two-junction tandem devices shows that for optimal device performance, the bandgap of the top cell should be around 1.6-1.8 eV. CdZnTe alloys can be tailored to yield bandgaps in the desired range. In this study, we considered were used to fabricate these films, using close-spaced sublimation (CSS) and radio-frequency sputtering (RFS) techniques. In the first approach, we used mixed powders of CdTe and ZnTe as the source for film deposition by CSS. Even for the ZnTe/CdTe (95:5 ratio) source material, the deposited films were entirely CdTe due to higher vapor pressure of CdTe. In the second approach, we used pre-alloyed CdZnTe powders (CERAC, Inc.) as the source. Due to the lower sticking coefficient of Zn, even for the source composition of 75% Zn, these films contained very low quantities of Zn (~5%). We tried unsuccessfully to increase the Zn content in the films by confining Zn vapor by enclosing the region between the source and substrate, reducing the substrate temperature to 400C, and adjusting the source/substance distance. Finally, we used thin-film couples consisting of 300-nm-thick CdTe deposited by CSS and 300-nm-thick ZnTe deposited by RFS; the samples were then heat-treated in cadmium chloride vapor. Compositional analysis of the samples showed extensive interdiffusion of Cd and Zn for the annealed samples. We will present the data on the various stack configurations of CdTe and ZnTe, the effect of different post-deposition anneals, the effect of oxygen on the interdiffusion and alloy formation and its possible correlation to the device performance degradation.

  13. The effects of deep level traps on the electrical properties of semi-insulating CdZnTe

    SciTech Connect

    Zha, Gangqiang; Yang, Jian; Xu, Lingyan; Feng, Tao; Wang, Ning; Jie, Wanqi

    2014-01-28

    Deep level traps have considerable effects on the electrical properties and radiation detection performance of high resistivity CdZnTe. A deep-trap model for high resistivity CdZnTe was proposed in this paper. The high resistivity mechanism and the electrical properties were analyzed based on this model. High resistivity CdZnTe with high trap ionization energy E{sub t} can withstand high bias voltages. The leakage current is dependent on both the deep traps and the shallow impurities. The performance of a CdZnTe radiation detector will deteriorate at low temperatures, and the way in which sub-bandgap light excitation could improve the low temperature performance can be explained using the deep trap model.

  14. A Monte Carlo simulation study of an improved K-edge log-subtraction X-ray imaging using a photon counting CdTe detector

    NASA Astrophysics Data System (ADS)

    Lee, Youngjin; Lee, Amy Candy; Kim, Hee-Joung

    2016-09-01

    Recently, significant effort has been spent on the development of photons counting detector (PCD) based on a CdTe for applications in X-ray imaging system. The motivation of developing PCDs is higher image quality. Especially, the K-edge subtraction (KES) imaging technique using a PCD is able to improve image quality and useful for increasing the contrast resolution of a target material by utilizing contrast agent. Based on above-mentioned technique, we presented an idea for an improved K-edge log-subtraction (KELS) imaging technique. The KELS imaging technique based on the PCDs can be realized by using different subtraction energy width of the energy window. In this study, the effects of the KELS imaging technique and subtraction energy width of the energy window was investigated with respect to the contrast, standard deviation, and CNR with a Monte Carlo simulation. We simulated the PCD X-ray imaging system based on a CdTe and polymethylmethacrylate (PMMA) phantom which consists of the various iodine contrast agents. To acquired KELS images, images of the phantom using above and below the iodine contrast agent K-edge absorption energy (33.2 keV) have been acquired at different energy range. According to the results, the contrast and standard deviation were decreased, when subtraction energy width of the energy window is increased. Also, the CNR using a KELS imaging technique is higher than that of the images acquired by using whole energy range. Especially, the maximum differences of CNR between whole energy range and KELS images using a 1, 2, and 3 mm diameter iodine contrast agent were acquired 11.33, 8.73, and 8.29 times, respectively. Additionally, the optimum subtraction energy width of the energy window can be acquired at 5, 4, and 3 keV for the 1, 2, and 3 mm diameter iodine contrast agent, respectively. In conclusion, we successfully established an improved KELS imaging technique and optimized subtraction energy width of the energy window, and based on

  15. Application of GaAs and CdTe photoconductor detectors to X-ray flash radiography

    NASA Astrophysics Data System (ADS)

    Mathy, F.; Cuzin, M.; Gagelin, J. J.; Mermet, R.; Piaget, B.; Rustique, J.; Verger, L.; Hauducoeur, A.; Nicolas, P.; Le Dain, L.; Hyvernage, M.

    1992-11-01

    Some insulating GaAs and CdTe:Cl photoconductor probes were qualified on high energy X-ray single-shot flash generators. The estimated minimum detected dose per flash corresponding to a 230 mrad direct beam attenuated by 200 mm lead was 20 μ rad. The dynamic range was about 4 decades in amplitude or charge, with a good linearity. Such detectors, by locating the origin of the parasitic scattered beam, could be used to eliminate this parasitic beam in X-ray flash radiography in detonics experiments. Imaging possibilities are mentioned, as well as X-ray generator monitoring with such detectors or with neutron preirradiated photoconductors.

  16. Purification of CdZnTe by Electromigration

    DOE PAGES

    Kim, K.; Kim, Sangsu; Hong, Jinki; Lee, Jinseo; Hong, Taekwon; Bolotnikov, A. E.; Camarda, G. S.; James, R. B.

    2015-04-14

    Electro-migration of ionized/electrically active impurities in CdZnTe (CZT) was successfully demonstrated at elevated temperature with an electric field of 20 V/mm. Copper, which exists in positively charged states, electro-migrated at a speed of 15 lm/h in an electric field of 20 V/mm. A notable variation in impurity concentration along the growth direction with the segregation tendency of the impurities was observed in an electro-migrated CZT boule. Notably, both Ga and Fe, which exist in positively charged states, exhibited the opposite distribution to that of their segregation tendency in Cd(Zn)Te. Furthermore, a CZT detector fabricated from the middle portion of themore » electromigrated CZT boule showed an improved mobility-lifetime product of 0.91 10-2 cm2 /V, compared to that of 1.4 10-3 cm2 /V, observed in an as-grown (non-electro-migrated) CZT detector. The optimum radiation detector material would have minimum concentration of deep traps required for compensation.« less

  17. Purification of CdZnTe by Electromigration

    SciTech Connect

    Kim, K.; Kim, Sangsu; Hong, Jinki; Lee, Jinseo; Hong, Taekwon; Bolotnikov, A. E.; Camarda, G. S.; James, R. B.

    2015-04-14

    Electro-migration of ionized/electrically active impurities in CdZnTe (CZT) was successfully demonstrated at elevated temperature with an electric field of 20 V/mm. Copper, which exists in positively charged states, electro-migrated at a speed of 15 lm/h in an electric field of 20 V/mm. A notable variation in impurity concentration along the growth direction with the segregation tendency of the impurities was observed in an electro-migrated CZT boule. Notably, both Ga and Fe, which exist in positively charged states, exhibited the opposite distribution to that of their segregation tendency in Cd(Zn)Te. Furthermore, a CZT detector fabricated from the middle portion of the electromigrated CZT boule showed an improved mobility-lifetime product of 0.91 10-2 cm2 /V, compared to that of 1.4 10-3 cm2 /V, observed in an as-grown (non-electro-migrated) CZT detector. The optimum radiation detector material would have minimum concentration of deep traps required for compensation.

  18. Purification of CdZnTe by electromigration

    SciTech Connect

    Kim, K.; Kim, Sangsu; Hong, Jinki; Lee, Jinseo; Hong, Taekwon; Bolotnikov, A. E.; Camarda, G. S.; James, R. B.

    2015-04-14

    Electro-migration of ionized/electrically active impurities in CdZnTe (CZT) was successfully demonstrated at elevated temperature with an electric field of 20 V/mm. Copper, which exists in positively charged states, electro-migrated at a speed of 15 μm/h in an electric field of 20 V/mm. A notable variation in impurity concentration along the growth direction with the segregation tendency of the impurities was observed in an electro-migrated CZT boule. Notably, both Ga and Fe, which exist in positively charged states, exhibited the opposite distribution to that of their segregation tendency in Cd(Zn)Te. A CZT detector fabricated from the middle portion of the electro-migrated CZT boule showed an improved mobility-lifetime product of 0.91 × 10{sup −2} cm{sup 2}/V, compared with that of 1.4 × 10{sup −3} cm{sup 2}/V, observed in an as-grown (non-electro-migrated) CZT detector. The optimum radiation detector material would have minimum concentration of deep traps required for compensation.

  19. Design of epitaxial CdTe solar cells on InSb substrates

    SciTech Connect

    Song, Tao; Kanevce, Ana; Sites, James R.

    2015-11-01

    Epitaxial CdTe has been shown by others to have a radiative recombination rate approaching unity, high carrier concentration, and low defect density. It has, therefore, become an attractive candidate for high-efficiency solar cells, perhaps becoming competitive with GaAs. The choice of substrate is a key design feature for epitaxial CdTe solar cells, and several possibilities (CdTe, Si, GaAs, and InSb) have been investigated by others. All have challenges, and these have generally been addressed through the addition of intermediate layers between the substrate and CdTe absorber. InSb is an attractive substrate choice for CdTe devices, because it has a close lattice match with CdTe, it has low resistivity, and it is easy to contact. However, the valence-band alignment between InSb and p-type CdTe, which can both impede hole current and enhance forward electron current, is not favorable. Three strategies to address the band-offset problem are investigated by numerical simulation: heavy doping of the back part of the CdTe layer, incorporation of an intermediate CdMgTe or CdZnTe layer, and the formation of an InSb tunnel junction. Lastly, wach of these strategies is predicted to be helpful for higher cell performance, but a combination of the first two should be most effective.

  20. Design of epitaxial CdTe solar cells on InSb substrates

    DOE PAGES

    Song, Tao; Kanevce, Ana; Sites, James R.

    2015-11-01

    Epitaxial CdTe has been shown by others to have a radiative recombination rate approaching unity, high carrier concentration, and low defect density. It has, therefore, become an attractive candidate for high-efficiency solar cells, perhaps becoming competitive with GaAs. The choice of substrate is a key design feature for epitaxial CdTe solar cells, and several possibilities (CdTe, Si, GaAs, and InSb) have been investigated by others. All have challenges, and these have generally been addressed through the addition of intermediate layers between the substrate and CdTe absorber. InSb is an attractive substrate choice for CdTe devices, because it has a closemore » lattice match with CdTe, it has low resistivity, and it is easy to contact. However, the valence-band alignment between InSb and p-type CdTe, which can both impede hole current and enhance forward electron current, is not favorable. Three strategies to address the band-offset problem are investigated by numerical simulation: heavy doping of the back part of the CdTe layer, incorporation of an intermediate CdMgTe or CdZnTe layer, and the formation of an InSb tunnel junction. Lastly, wach of these strategies is predicted to be helpful for higher cell performance, but a combination of the first two should be most effective.« less

  1. ADVANCED READOUT ELECTRONICS FOR MULTIELEMENT CdZnTe SENSORS.

    SciTech Connect

    DE GERONIMO,G.; O CONNOR,P.; KANDASAMY,A.; GROSHOLZ,J.

    2002-07-08

    A generation of high performance front-end and read-out ASICs customized for highly segmented CdZnTe sensors is presented. The ASICs, developed in a multi-year effort at Brookhaven National Laboratory, are targeted to a wide range of applications including medical, safeguards/security, industrial, research, and spectroscopy. The front-end multichannel ASICs provide high accuracy low noise preamplification and filtering of signals, with versions for small and large area CdZnTe elements. They implement a high order unipolar or bipolar shaper, an innovative low noise continuous reset system with self-adapting capability to the wide range of detector leakage currents, a new system for stabilizing the output baseline and high output driving capability. The general-purpose versions include programmable gain and peaking time. The read-out multichannel ASICs provide fully data driven high accuracy amplitude and time measurements, multiplexing and time domain derandomization of the shaped pulses. They implement a fast arbitration scheme and an array of innovative two-phase offset-free rail-to-rail analog peak detectors for buffering and absorption of input rate fluctuations, thus greatly relaxing the rate requirement on the external ADC. Pulse amplitude, hit timing, pulse risetime, and channel address per processed pulse are available at the output in correspondence of an external readout request. Prototype chips have been fabricated in 0.5 and 0.35 {micro}m CMOS and tested. Design concepts and experimental results are discussed.

  2. Position resolution performance of prototype segmented CdZnTe arrays

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Palmer, David M.; Kurczynski, P.; Barbier, Louis M.; Barthelmy, Scott D.; Bartlett, Lyle M.; Gehrels, Neil A.; Krizmanic, John F.; Stahle, Carl M.; Tueller, Jack; Teegarden, Bonnard J.

    1997-10-01

    The burst and all sky imaging survey (BASIS) is a proposed mission to provide plus or minus 3 arc-second locations of an estimated 90 gamma-ray bursts (GRBs) per year. The BASIS coded aperture imaging system requires a segmented detector plane able to detect the position of photon absorption to less than 100 microns. To develop prototype detector arrays with such fine position resolution we have fabricated many 15 mm by 15 mm by 2 mm 100 micron pitch CdZnTe strip detectors. A 2 by 2 prototype 100 micron CdZnTe strip detector array has been fabricated and has been used to test the capabilities of the BASIS imaging system. Preliminary shadowgrams of a 1 mm wide gap between two tungsten straight edges indicate that our position resolution is on the order of 69 micrometers. Both the array and imaging tests are described. A 6 by 6 element CdZnTe detector array is also being fabricated at GSFC. The assembly of this flight prototype array is discussed as well as applications for BASIS.

  3. Cadmium Manganese Telluride (Cd1-xMnxTe): A potential material for room-temperature radiation detectors

    SciTech Connect

    Hossain, A.; Cui, Y.; Bolotnikov, A.; Camarda, G.; Yang, G.; Kim, K-H.; Gul, R.; Xu, L.; Li, L.; Mycielski, A.; and James, R.B.

    2010-07-11

    Cadmium Manganese Telluride (CdMnTe) recently emerged as a promising material for room-temperature X- and gamma-ray detectors. It offers several potential advantages over CdZnTe. Among them is its optimal tunable band gap ranging from 1.7-2.2 eV, and its relatively low (< 50%) content of Mn compared to that of Zn in CdZnTe that assures this favorable band-gap range. Another important asset is the segregation coefficient of Mn in CdTe that is approximately unity compared to 1.35 for Zn in CdZnTe, so ensuring the homogenous distribution of Mn throughout the ingot; hence, a large-volume stoichiometric yield is attained. However, some materials issues primarily related to the growth process impede the production of large, defect-free single crystals. The high bond-ionicity of CdMnTe entails a higher propensity to crystallize into a hexagonal structure rather than to adopt the expected zinc-blend structure, which is likely to generate twins in the crystals. In addition, bulk defects generate in the as-grown crystals due to the dearth of high-purity Mn, which yields a low-resistivity material. In this presentation, we report on our observations of such material defects in current CdMnTe materials, and our evaluation of its potential as an alternative detector material to the well-known CdZnTe detectors. We characterized the bulk defects of several indium- and vanadium-doped Cd1-xMnxTe crystals by using several advanced techniques, viz., micro-scale mapping, white-beam x-ray diffraction/reflection topography, and chemical etching. Thereafter, we fabricated some detectors from selected CdMnTe crystals, characterized their electrical properties, and tested their performance as room-temperature X- and gamma-ray detectors. Our experimental results indicate that CdMnTe materials could well prove to become a viable alternative in the near future.

  4. Molecular Beam Epitaxy Growth of HgCdTe on Large-Area Si and CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Reddy, M.; Peterson, J. M.; Vang, T.; Franklin, J. A.; Vilela, M. F.; Olsson, K.; Patten, E. A.; Radford, W. A.; Bangs, J. W.; Melkonian, L.; Smith, E. P. G.; Lofgreen, D. D.; Johnson, S. M.

    2011-08-01

    This paper presents the status of HgCdTe growth on large-area Si and CdZnTe substrates at Raytheon Vision Systems (RVS). The different technological tools that were used to scale up the growth from 4 inch to 6 inch diameter on Si and from 4 cm × 4 cm to 8 cm × 8 cm on CdZnTe without sacrificing the quality of the layers are described. Extremely high compositional uniformity and low macrodefect density were achieved for single- and two-color HgCdTe layers on both Si and CdZnTe substrates. Finally, a few examples of detector and focal-plane array results are included to highlight the importance of high compositional uniformity and uniformly low macrodefect density of the epitaxial layers in obtaining high operability and low cluster outages in single- and two-color focal-plane arrays (FPAs).

  5. High Efficiency Single Crystal CdTe Solar Cells: November 19, 2009 - January 31, 2011

    SciTech Connect

    Carmody, M.; Gilmore, A.

    2011-05-01

    The goal of the program was to develop single crystal CdTe-based top cells grown on Si solar cells as a platform for the subsequent manufacture of high efficiency tandem cells for CPV applications. The keys to both the single junction and the tandem junction cell architectures are the ability to grow high quality single-crystal CdTe and CdZnTe layers on p-type Si substrates, to dope the CdTe and CdZnTe controllably, both n and p-type, and to make low resistance ohmic front and back contacts. EPIR demonstrated the consistent MBE growth of CdTe/Si and CdZnTe/Si having high crystalline quality despite very large lattice mismatches; epitaxial CdTe/Si and CdZnTe/Si consistently showed state-of-the-art electron mobilities and good hole mobilities; bulk minority carrier recombination lifetimes of unintentionally p-doped CdTe and CdZnTe grown by MBE on Si were demonstrated to be consistently of order 100 ns or longer; desired n- and p-doping levels were achieved; solar cell series specific resistances <10 ?-cm2 were achieved; A single-junction solar cell having a state-of-the-art value of Voc and a unverified 16.4% efficiency was fabricated from CdZnTe having a 1.80 eV bandgap, ideal for the top junction in a tandem cell with a Si bottom junction.

  6. Effect of ampoule coating technology on defects in CdZnTe crystal

    NASA Astrophysics Data System (ADS)

    Liu, Congfeng; Sun, Shiwen; Xu, Hualian

    2008-12-01

    Inclusions and micro-defects revealed by etch pits are the main defects of CdZnTe crystal, which can not be eliminated thoroughly at present. These defects will affect the photoelectric characteristic of CdZnTe and the quality of the MCT epilayer used for the infrared detectors. Many technologies are employed to suppress or eliminate the defects of CdZnTe materials, and one of them is ampoule coating technology. In the paper, ordinary carbon coating, improved carbon coating and BN (Boron Nitride) coating technology were used to study their effects on defects in CdZnTe crystal. After carbon coating technology was improved, the size of inclusion in the crystal had an obvious decrease from more than 30 μm to less than 15 μm, the density of inclusion reduced from 3~6×104cm-3 to 2×104cm-3, and etch pits density(EPD) reduced from 1×105cm-2 to less than 5×104cm-2. This meant carbon film breaking off from the ampoule was major factors to form inclusion with high density and large size, and high EPD might be relative with impurities in the material. The size of inclusions and the densities of inclusion and etch pits could be further decreased to less than 5 μm, 4×103cm-3 and 1×104cm-2 respectively after taking BN coating technology, while cell structure of etch pits found in the previous CdZnTe wafers disappeared. This result further showed that high density of inclusion and EPD originated from carbon impurities in the materials.

  7. LIGHT INDUCED TELLURIUM ENRICHMENT ON CDZNTE CRYSTALSURFACES DETECTED BY RAMAN SPECTROSCOPY

    SciTech Connect

    Hawkins, S; Eliel Villa-Aleman, E; Martine Duff, M; Douglas02 Hunter, D

    2007-10-29

    Synthetic CdZnTe or 'CZT' crystals can be grown under controlled conditions to produce high quality crystals to be used as room temperature radiation detectors. Even the best crystal growth methods result in defects, such as tellurium secondary phases, that affect the crystal's performance. In this study, CZT crystals were analyzed by micro Raman spectroscopy. The growth of Te rich areas on the surface was induced by low powered lasers. The growth was observed versus time with low power Raman scattering and was observed immediately under higher power conditions. The detector response was also measured after induced Te enrichment.

  8. Resistive switching properties in CdZnTe films

    SciTech Connect

    Zha, Gangqiang; Lin, Yun; Tan, Tingting; Jie, Wanqi; Zeng, Dongmei

    2015-02-09

    The ternary II–VI compound semiconductor cadmium zinc telluride (CdZnTe) has bi-stable conduction characteristics. In this letter, CdZnTe films are grown on indium tin oxide (ITO) substrates by radio frequency magnetron sputtering. The current-voltage characteristics show that there is resistive switching in a structure consisting of an 800-nm-thick CdZnTe film, an Au Schottky contact, and an ITO bottom electrode. The electroresistance in Au/CdZnTe/ITO may be related to the polarization of the CdZnTe film and the Schottky contact.

  9. Simulation and Analysis of Large-Scale Compton Imaging Detectors

    SciTech Connect

    Manini, H A; Lange, D J; Wright, D M

    2006-12-27

    We perform simulations of two types of large-scale Compton imaging detectors. The first type uses silicon and germanium detector crystals, and the second type uses silicon and CdZnTe (CZT) detector crystals. The simulations use realistic detector geometry and parameters. We analyze the performance of each type of detector, and we present results using receiver operating characteristics (ROC) curves.

  10. CHARACTERIZATION OF SECONDARY PHASES AND OTHER DEFECTS IN CDZNTE

    SciTech Connect

    Duff, M.

    2010-06-30

    Semiconducting CdZnTe or 'CZT' crystals are very suitable for use as a room temperature-based gamma radiation spectrometer. During the last decade, modifications in growth methods for CZT have significantly improved the quality of the produced crystals however there are material features that can influence the performance of these materials as radiation detectors. For example, various structural heterogeneities within the CZT crystals, such as, pipes, voids, polycrystallinity, and secondary phases (SP) can have a negative impact on the detector performance. In this study, a CZT material was grown by the modified vertical Bridgman growth (MVB) method with zone leveled growth in the absence of excess Te in the melt. Numerous SP were imaged using transmission IR at a volume % of 0.002. Samples from this material were analyzed using various analytical techniques to evaluate its electrical properties, purity and detector performance as radiation spectrometers and to determine the morphology, dimension and elemental /structural composition of one of the SP in this material. This material was found to have a high resistivity and good radiation spectrometer performance. It had SPs that were rich in calcium (Ca), carbon (C) and oxygen (O) (possibly CaCO{sub 3}) or only C and O that were 5 {micro}m or less in diameter.

  11. Distribution of Te inclusions in a CdZnTe wafer and their effects on the electrical properties of fabricated devices

    SciTech Connect

    Hossain , A.; Xu, L.; Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Yang, G.; Kim, K.-H.; and James, R.B.

    2010-05-24

    We quantified the size and concentration of Te-inclusions along the lateral- and the growth-directions of a {approx}6 mm thick wafer cut axially along the center of a CdZnTe ingot. We fabricated devices, selecting samples from the center slice outward in both directions, and then tested their response to incident x-rays. We employed, in concert, an automated IR transmission microscopic system and a highly collimated synchrotron X-ray source that allowed us to acquire and correlate comprehensive information on Te inclusions and other defects to assess the material factors limiting the performance of CdZnTe detectors.

  12. Live-monitoring of Te inclusions laser-induced thermo-diffusion and annealing in CdZnTe crystals

    SciTech Connect

    Zappettini, A.; Zambelli, N.; Benassi, G.; Calestani, D.; Pavesi, M.

    2014-06-23

    The presence of Te inclusions is one of the main factors limiting performances of CdZnTe crystals as X-ray detectors. We show that by means of infrared laser radiation it is possible to move and anneal tellurium inclusions exploiting a thermo-diffusion mechanism. The process is studied live during irradiation by means of an optical microscope equipment. Experimental conditions, and, in particular, energy laser fluence, for annealing inclusions of different dimensions are determined.

  13. Study of asymmetries of Cd(Zn)Te devices investigated using photo-induced current transient spectroscopy, Rutherford backscattering, surface photo-voltage spectroscopy, and gamma ray spectroscopies

    SciTech Connect

    Crocco, J.; Bensalah, H.; Zheng, Q.; Dieguez, E.; Corregidor, V.; Avles, E.; Castaldini, A.; Fraboni, B.; Cavalcoli, D.; Cavallini, A.; Vela, O.

    2012-10-01

    Despite these recent advancements in preparing the surface of Cd(Zn)Te devices for detector applications, large asymmetries in the electronic properties of planar Cd(Zn)Te detectors are common. Furthermore, for the development of patterned electrode geometries, selection of each electrode surface is crucial for minimizing dark current in the device. This investigation presented here has been carried out with three objectives. Each objective is oriented towards establishing reliable methods for the selection of the anode and cathode surfaces independent of the crystallographic orientation. The objectives of this study are (i) investigate how the asymmetry in I-V characteristics of Cd(Zn)Te devices may be associated with the TeO2 interfacial layer using Rutherford backscattering to study the structure at the Au-Cd(Zn)Te interface, (ii) develop an understanding of how the concentration of the active traps in Cd(Zn)Te varies with the external bias, and (iii) propose non-destructive methods for selection of the anode and cathode which are independent of crystallographic orientation. The spectroscopic methods employed in this investigation include Rutherford backscattering spectroscopy, photo-induced current transient spectroscopy, and surface photo-voltage spectroscopy, as well as gamma ray spectroscopy to demonstrate the influence on detector properties.

  14. Crystal Growth of CdTe by Gradient Freeze in Universal Multizone Crystallizator (UMC)

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hua; Lehoczky, S. L.; Li, C.; Knuteson, D.; Raghothamachar, B.; Dudley, M.; Szoke, J.; Barczy, P.

    2004-01-01

    In the case of unsealed melt growth of an array of II-VI compounds, namely, CdTe, CdZnTe and ZnSe, there is a tremendous amount of experimental data describing the correlations between melt conditions and crystal quality. The results imply that the crystallinity quality can be improved if the melt was markedly superheated or long-time held before growth. It is speculated that after high superheating the associated complex dissociate and the spontaneous nucleation is retarded. In this study, crystals of CdTe were grown from melts which have undergone different thermal history by the unseeded gradient freeze method using the Universal Multizone Crystallizator (UMC). The effects of melt conditions on the quality of grown crystal were studied by various characterization techniques, including Synchrotron White Beam X-ray Topography (SWSXT), infrared microscopy, chemical analysis by glow discharge mass spectroscopy (GDMS), electrical conductivity and Hall measurements.

  15. Material analysis of the CZT crystal grown for a radiation detector

    NASA Astrophysics Data System (ADS)

    Kim, Han Soo; Jeong, Manhee; Kim, Young Soo; Kim, Dong Jin; Choi, Hyo Jeong

    2015-01-01

    Room-temperature semiconductor radiation detectors, such as CdZnTe (CZT) and CdTe detectors, are being developed and grown worldwide owing to their high performances as a gamma-ray detector. A 2″ CZT ingot was grown using a 6-zone low-pressure (LP) Bridgman furnace at the Korea Atomic Energy Research Institute (KAERI). To increase the resistivity, indium (In) was doped at 5 ppm and 7 ppm, respectively. Material analysis results obtained by using inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffractometry (XRD), and an infrared (IR) scope system were compared with the I-V results with respect to the location on the grown ingots and doping concentration. A (1,1,1) orientation and 1.41 × 1011 Ω·cm resistivity were measured in the middle part of the ingot. In addition, Te inclusions were also homogeneously shown. The variation in the I-V characteristics with respect to the preparation conditions of the crystals was also addressed.

  16. Progress in the development of large-area modular 64 x 64 CdZnTe imaging arrays for nuclear medicine

    SciTech Connect

    Matherson, K.J.; Barber, H.B.; Barrett, H.H.; Eskin, J.D.; Dereniak, E.L.; Marks, D.G.; Woolfenden, J.M.; Young, E.T.; Augustine, F.L.

    1998-06-01

    Previous efforts by this group have demonstrated the potential of hybrid semiconductor detector arrays for use in gamma-ray imaging applications. In this paper, the author describes progress in the development of a prototype imaging system consisting of a 64 x 64-pixel CdZnTe detector array mated to a multiplexer readout circuit that was custom designed for their nuclear medicine application. The detector array consists of a 0.15 cm thick slab of CdZnTe which has a 64 x 64 array of 380 {micro}m square pixel electrodes on one side produced by photolithography; the other side has a continuous electrode biased at {minus}150 V. Electrical connections between the detector electrodes and corresponding multiplexer bump pads are made with indium bump bonds. Although the CdZnTe detector arrays characterized in this paper are room-temperature devices, a slight amount of cooling is necessary to reduce thermally generated dark current in the detectors. Initial tests show that this prototype imager functions well with more than 90% of its pixels operating. The device is an excellent imager; phantom images have a spatial resolution of 1.5 mm, limited by the collimator bore.

  17. Gamma-Ray Detectors: From Homeland Security to the Cosmos (443rd Brookhaven Lecture)

    SciTech Connect

    Bolotnikov, Aleksey

    2008-12-03

    Many radiation detectors are first developed for homeland security or industrial applications. Scientists, however, are continuously realizing new roles that these detectors can play in high-energy physics and astrophysics experiments. On Wednesday, December 3, join presenter Aleksey Bolotnikov, a physicist in the Nonproliferation and National Security Department (NNSD) and a co-inventor of the cadmium-zinc-telluride Frisch-ring (CdZnTe) detector, for the 443rd Brookhaven Lecture, entitled Gamma-Ray Detectors: From Homeland Security to the Cosmos. In his lecture, Bolotnikov will highlight two primary radiation-detector technologies: CdZnTe detectors and fluid-Xeon (Xe) detectors.

  18. Mercury cadmium telluride infrared detector development in India: status and issues

    NASA Astrophysics Data System (ADS)

    Singh, R. N.

    2009-05-01

    In the present paper, we describe the development of Long Wave Infrared (8-12 μm) linear and 2-D IR FPA detectors using HgCdTe for use in thermal imagers and IIR seekers. In this direction, Solid State Physics Laboratory(SSPL) (DRDO) tried to concentrate initially in the bulk growth and characterization of HgCdTe during the early eighties. Some efforts were then made to develop a LWIR photoconductive type MCT array in linear configuration with the IRFPA processed on bulk MCT crystals grown in the laboratory. Non availability of quality epilayers with the required specification followed by the denial of supply of CdTe, CdZnTe and even high purity Te by advanced countries, forced us to shift our efforts during early nineties towards development of 60 element PC IR detectors. High performance linear PC arrays were developed. A novel horizontal casting procedure was evolved for growing high quality bulk material using solid state recrystallization technique. Efforts for ultra purification of Te to 7N purity with the help of a sister concern has made it possible to have this material indigenously. Having succeded in the technology for growing single crystalline CdZnTe with (111) orientation and LPE growth of HgCdTe epilayers on CdZnTe substrates an attempt was made to establish the fabrication of 2D short PV arrays showing significant IR response. Thus a detailed technological knowhow for passivation, metallization, ion implanted junction formation, etc. was generated. Parallel work on the development of a matching CCD Mux readout in silicon by Semiconductor Complex Limited was also completed which was tested first in stand-alone mode followed by integration with IRFPAs through indigenously-developed indium bumps. These devices were integrated into an indigenously fabricated glass dewar cooled by a self-developed JT minicooler. In recent years, the LPE (Liquid Phase Epitaxy) growth from Terich route has been standardized for producing epitaxial layers with high

  19. Applications of CdTe to nuclear medicine. Final report

    SciTech Connect

    Entine, G.

    1985-05-07

    Uses of cadmium telluride (CdTe) nuclear detectors in medicine are briefly described. They include surgical probes and a system for measuring cerebral blood flow in the intensive care unit. Other uses include nuclear dentistry, x-ray exposure control, cardiology, diabetes, and the testing of new pharmaceuticals. (ACR)

  20. Analysis of Etched CdZnTe Substrates

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Arias, J. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Jones, K.; Johnson, S. M.; Lofgreen, D. D.

    2016-09-01

    State-of-the-art as-received (112)B CdZnTe substrates have been examined for surface impurity contamination and polishing residue. Two 4 cm × 4 cm and one 6 cm × 6 cm (112)B state-of-the-art as-received CdZnTe wafers were analyzed. A maximum surface impurity concentration of Al = 1.7 × 1015 atoms cm-2, Si = 3.7 × 1013 atoms cm-2, Cl = 3.12 × 1015 atoms cm-2, S = 1.7 × 1014 atoms cm-2, P = 1.1 × 1014 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 1.2 × 1014 atoms cm-2, and Cu = 4 × 1012 atoms cm-2 was observed on the as-received CdZnTe wafers. CdZnTe particulates and residual SiO2 polishing grit were observed on the surface of the as-received (112)B CdZnTe substrates. The polishing grit/CdZnTe particulate density on CdZnTe wafers was observed to vary across a 6 cm × 6 cm wafer from ˜4 × 107 cm-2 to 2.5 × 108 cm-2. The surface impurity and damage layer of the (112)B CdZnTe wafers dictate that a molecular beam epitaxy (MBE) preparation etch is required. The contamination for one 4 cm × 4 cm and one 6 cm × 6 cm CdZnTe wafer after a standard MBE Br:methanol preparation etch procedure was also analyzed. A maximum surface impurity concentration of Al = 2.4 × 1015 atoms cm-2, Si = 4.0 × 1013 atoms cm-2, Cl = 7.5 × 1013 atoms cm-2, S = 4.4 × 1013 atoms cm-2, P = 9.8 × 1013 atoms cm-2, Fe = 1.0 × 1013 atoms cm-2, Br = 2.9 × 1014 atoms cm-2, and Cu = 5.2 × 1012 atoms cm-2 was observed on the MBE preparation-etched CdZnTe wafers. The MBE preparation-etched surface contamination consists of Cd(Zn)Te particles/flakes. No residual SiO2 polishing grit was observed on the (112)B surface.

  1. Room temperature semiconductor detectors for hard x-ray astrophysics

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Stahle, Carl M.; Lisse, Casey M.; Babu, Sachi; Gehrels, Neil A.; Teegarden, Bonnard J.; Shu, Peter K.

    1994-09-01

    Room temperature cadmium zinc telluride (CdZnTe) and mercuric iodide (HgI2) semiconductor hard X-ray detectors are currently being evaluated at NASA Goddard Space Flight Center for use in future balloon and satellite applications. PoRTIA, a small engineering prototype hard X-ray (20 - 150 keV) balloon instrument will contain both a CdZnTe and a HgI2 detector, each 6.5 cm2 x .15 - .2 cm and sharing the same 5 degree(s) field-of-view. PoRTIA will be launched from Alice Springs, Australia in the Spring of 1995 as a piggyback instrument aboard the GRIS balloon payload. PoRTIA will provide valuable information about detector efficiency, durability and material dependent detector background components at balloon altitudes as it observes the Crab Nebula. In addition, a CdZnTe research and development program has been initiated to develop the capability to produce improved CdZnTe detectors for astrophysics applications. The work at Goddard continues in an effort to develop CdZnTe detectors with improvements in electronics, contacts and packaging methods.

  2. Mechanisms of the passage of dark currents through Cd(Zn)Te semi-insulating crystals

    NASA Astrophysics Data System (ADS)

    Sklyarchuk, V.; Fochuk, P.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O.; Nykoniuk, Ye.; Rybka, A.; Kutny, V.; Bolotnikov, A. E.; James, R. B.

    2014-09-01

    We investigated the passage of dark currents through semi-insulating crystals of Cd(Zn)Te with weak n-type conductivity that are used widely as detectors of ionizing radiation. The crystals were grown from a tellurium solution melt at 800 оС by the zone-melting method, in which a polycrystalline rod in a quartz ampoule was moved through a zone heater at a rate of 2 mm per day. The synthesis of the rod was carried out at ~1150 оС. We determined the important electro-physical parameters of this semiconductor, using techniques based on a parallel study of the temperature dependence of current-voltage characteristics in both the ohmic and the space-charge-limited current regions. We established in these crystals the relationship between the energy levels and the concentrations of deep-level impurity states, responsible for dark conductivity and their usefulness as detectors.

  3. Pixellated Cd(Zn)Te high-energy X-ray instrument

    NASA Astrophysics Data System (ADS)

    Seller, P.; Bell, S.; Cernik, R. J.; Christodoulou, C.; Egan, C. K.; Gaskin, J. A.; Jacques, S.; Pani, S.; Ramsey, B. D.; Reid, C.; Sellin, P. J.; Scuffham, J. W.; Speller, R. D.; Wilson, M. D.; Veale, M. C.

    2011-12-01

    We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 μm by 250 μm give better than 1 keV FWHM energy resolution at 59.5 keV and 1.5 keV FWHM at 141 keV, at the same time providing a high speed imaging performance. This system uses a relatively simple wire-bonded interconnection scheme but this is being upgraded to allow multiple modules to be used with very small dead space. The readout system and the novel interconnect technology is described and how the system is performing in several target applications.

  4. Pixellated Cd(Zn)Te high-energy X-ray instrument

    PubMed Central

    Seller, P.; Bell, S.; Cernik, R.J.; Christodoulou, C.; Egan, C.K.; Gaskin, J.A.; Jacques, S.; Pani, S.; Ramsey, B.D.; Reid, C.; Sellin, P.J.; Scuffham, J.W.; Speller, R.D.; Wilson, M.D.; Veale, M.C.

    2012-01-01

    We have developed a pixellated high energy X-ray detector instrument to be used in a variety of imaging applications. The instrument consists of either a Cadmium Zinc Telluride or Cadmium Telluride (Cd(Zn)Te) detector bump-bonded to a large area ASIC and packaged with a high performance data acquisition system. The 80 by 80 pixels each of 250 μm by 250 μm give better than 1 keV FWHM energy resolution at 59.5 keV and 1.5 keV FWHM at 141 keV, at the same time providing a high speed imaging performance. This system uses a relatively simple wire-bonded interconnection scheme but this is being upgraded to allow multiple modules to be used with very small dead space. The readout system and the novel interconnect technology is described and how the system is performing in several target applications. PMID:22737179

  5. CdTe Timepix detectors for single-photon spectroscopy and linear polarimetry of high-flux hard x-ray radiation.

    PubMed

    Hahn, C; Weber, G; Märtin, R; Höfer, S; Kämpfer, T; Stöhlker, Th

    2016-04-01

    Single-photon spectroscopy of pulsed, high-intensity sources of hard X-rays - such as laser-generated plasmas - is often hampered by the pileup of several photons absorbed by the unsegmented, large-volume sensors routinely used for the detection of high-energy radiation. Detectors based on the Timepix chip, with a segmentation pitch of 55 μm and the possibility to be equipped with high-Z sensor chips, constitute an attractive alternative to commonly used passive solutions such as image plates. In this report, we present energy calibration and characterization measurements of such devices. The achievable energy resolution is comparable to that of scintillators for γ spectroscopy. Moreover, we also introduce a simple two-detector Compton polarimeter setup with a polarimeter quality of (98 ± 1)%. Finally, a proof-of-principle polarimetry experiment is discussed, where we studied the linear polarization of bremsstrahlung emitted by a laser-driven plasma and found an indication of the X-ray polarization direction depending on the polarization state of the incident laser pulse. PMID:27131653

  6. CdTe Timepix detectors for single-photon spectroscopy and linear polarimetry of high-flux hard x-ray radiation

    NASA Astrophysics Data System (ADS)

    Hahn, C.; Weber, G.; Märtin, R.; Höfer, S.; Kämpfer, T.; Stöhlker, Th.

    2016-04-01

    Single-photon spectroscopy of pulsed, high-intensity sources of hard X-rays — such as laser-generated plasmas — is often hampered by the pileup of several photons absorbed by the unsegmented, large-volume sensors routinely used for the detection of high-energy radiation. Detectors based on the Timepix chip, with a segmentation pitch of 55 μm and the possibility to be equipped with high-Z sensor chips, constitute an attractive alternative to commonly used passive solutions such as image plates. In this report, we present energy calibration and characterization measurements of such devices. The achievable energy resolution is comparable to that of scintillators for γ spectroscopy. Moreover, we also introduce a simple two-detector Compton polarimeter setup with a polarimeter quality of (98 ± 1)%. Finally, a proof-of-principle polarimetry experiment is discussed, where we studied the linear polarization of bremsstrahlung emitted by a laser-driven plasma and found an indication of the X-ray polarization direction depending on the polarization state of the incident laser pulse.

  7. Effect of charge trapping on effective carrier lifetime in compound semiconductors: High resistivity CdZnTe

    SciTech Connect

    Kamieniecki, Emil

    2014-11-21

    The dominant problem limiting the energy resolution of compound semiconductor based radiation detectors is the trapping of charge carriers. The charge trapping affects energy resolution through the carrier lifetime more than through the mobility. Conventionally, the effective carrier lifetime is determined using a 2-step process based on measurement of the mobility-lifetime product (μτ) and determining drift mobility using time-of-flight measurements. This approach requires fabrication of contacts on the sample. A new RF-based pulse rise-time method, which replaces this 2-step process with a single non-contact direct measurement, is discussed. The application of the RF method is illustrated with high-resistivity detector-grade CdZnTe crystals. The carrier lifetime in the measured CdZnTe, depending on the quality of the crystals, was between about 5 μs and 8 μs. These values are in good agreement with the results obtained using conventional 2-step approach. While the effective carrier lifetime determined from the initial portion of the photoresponse transient combines both recombination and trapping in a manner similar to the conventional 2-step approach, both the conventional and the non-contact RF methods offer only indirect evaluation of the effect of charge trapping in the semiconductors used in radiation detectors. Since degradation of detector resolution is associated not with trapping but essentially with detrapping of carriers, and, in particular, detrapping of holes in n-type semiconductors, it is concluded that evaluation of recombination and detrapping during photoresponse decay is better suited for evaluation of compound semiconductors used in radiation detectors. Furthermore, based on previously reported data, it is concluded that photoresponse decay in high resistivity CdZnTe at room temperature is dominated by detrapping of carriers from the states associated with one type of point defect and by recombination of carriers at one type of

  8. Detectors

    DOEpatents

    Orr, Christopher Henry; Luff, Craig Janson; Dockray, Thomas; Macarthur, Duncan Whittemore; Bounds, John Alan; Allander, Krag

    2002-01-01

    The apparatus and method provide techniques through which both alpha and beta emission determinations can be made simultaneously using a simple detector structure. The technique uses a beta detector covered in an electrically conducting material, the electrically conducting material discharging ions generated by alpha emissions, and as a consequence providing a measure of those alpha emissions. The technique also offers improved mountings for alpha detectors and other forms of detectors against vibration and the consequential effects vibration has on measurement accuracy.

  9. Polarimetric performance of a Laue lens gamma-ray CdZnTe focal plane prototype

    SciTech Connect

    Curado da Silva, R. M.; Caroli, E.; Stephen, J. B.; Schiavone, F.; Donati, A.; Ventura, G.; Pisa, A.; Auricchio, N.; Frontera, F.; Del Sordo, S.; Honkimaeki, V.; Trindade, A. M. F.

    2008-10-15

    A gamma-ray telescope mission concept [gamma ray imager (GRI)] based on Laue focusing techniques has been proposed in reply to the European Space Agency call for mission ideas within the framework of the next decade planning (Cosmic Vision 2015-2025). In order to optimize the design of a focal plane for this satellite mission, a CdZnTe detector prototype has been tested at the European Synchrotron Radiation Facility under an {approx}100% polarized gamma-ray beam. The spectroscopic, imaging, and timing performances were studied and in particular its potential as a polarimeter was evaluated. Polarization has been recognized as being a very important observational parameter in high energy astrophysics (>100 keV) and therefore this capability has been specifically included as part of the GRI mission proposal. The prototype detector tested was a 5 mm thick CdZnTe array with an 11x11 active pixel matrix (pixel area of 2.5x2.5 mm{sup 2}). The detector was irradiated by a monochromatic linearly polarized beam with a spot diameter of about 0.5 mm over the energy range between 150 and 750 keV. Polarimetric Q factors of 0.35 and double event relative detection efficiency of 20% were obtained. Further measurements were performed with a copper Laue monochromator crystal placed between the beam and the detector prototype. In this configuration we have demonstrated that a polarized beam does not change its polarization level and direction after undergoing a small angle (<1 deg.) Laue diffraction inside a crystal.

  10. A 48x48 CdZnTe array with multiplexer readout

    SciTech Connect

    Marks, D.G.; Barber, H.B.; Barrett, H.H.

    1996-06-01

    The authors report results of gamma-ray imaging and energy-resolution tests of a 48x48 CdZnTe array. The detectors have 125 {micro}m square pixel electrodes produced by photolithography and are indium-bump-bonded to a multiplexer readout circuit. Using a collimated beam of 140 keV gamma rays of 120 {micro}m diameter centered on one pixel, they found that the majority of events produced significant charge deposition in nearby pixels. Charge and energy are transported out of the pixel by charge diffusion, photoelectron range, Compton scattering, and escape of K x-rays. These effects also distort single-pixel spectra, although photopeaks are still discernible at 140 keV. When signals from neighboring pixels are summed together to correct for this charge spreading, an energy resolution of 10 keV is obtained at 140 keV. Corrections will be simpler and energy resolution should be better for the 380 {micro}m pixels of the 64x64 CdZnTe arrays the authors are constructing for an ultra-high-resolution brain imager.

  11. CdZnTe background measurements at balloon altitudes

    NASA Astrophysics Data System (ADS)

    Parsons, Ann M.; Barthelmy, Scott D.; Bartlett, Lyle M.; Birsa, F. B.; Gehrels, Neil A.; Naya, Juan E.; Odom, James L.; Singh, S.; Stahle, Carl M.; Tueller, Jack; Teegarden, Bonnard J.

    1996-10-01

    Because of its high atomic number and convenient room temperature operation, CdZnTe has great potential for use in both balloon and space borne hard x-ray (5 - 200 keV) astrophysics experiments. Here we present preliminary results from the first CdZnTe background measurements made by a balloon instrument. Measurements of the CdZnTe internal background are essential to determine which physical processes make the most important background contributions and are critical in the design of future scientific instruments. The PoRTIA CdZnTe balloon instrument was flown three times in three different shielding configurations. PoRTIA was passively shielded during its first flight from Palestine, Texas and actively shielded as a piggyback instrument on the GRIS balloon experiment during flights 2 and 3 from Alice Springs, Australia. PoRTIA flew twice during the Fall 1995 Alice Springs, Australia campaign using the thick GRIS NaI anticoincidence shield. A significant CdZnTe background reduction was achieved during the third flight with PoRTIA placed completely inside the GRIS shield and blocking crystal, and thus completely surrounded by 15 cm of NaI. These background results are presented and contributions from different background processes are discussed.

  12. Simulation of charge transport in pixelated CdTe

    NASA Astrophysics Data System (ADS)

    Kolstein, M.; Ariño, G.; Chmeissani, M.; De Lorenzo, G.

    2014-12-01

    The Voxel Imaging PET (VIP) Pathfinder project intends to show the advantages of using pixelated semiconductor technology for nuclear medicine applications to achieve an improved image reconstruction without efficiency loss. It proposes designs for Positron Emission Tomography (PET), Positron Emission Mammography (PEM) and Compton gamma camera detectors with a large number of signal channels (of the order of 106). The design is based on the use of a pixelated CdTe Schottky detector to have optimal energy and spatial resolution. An individual read-out channel is dedicated for each detector voxel of size 1 × 1 × 2 mm3 using an application-specific integrated circuit (ASIC) which the VIP project has designed, developed and is currently evaluating experimentally. The behaviour of the signal charge carriers in CdTe should be well understood because it has an impact on the performance of the readout channels. For this purpose the Finite Element Method (FEM) Multiphysics COMSOL software package has been used to simulate the behaviour of signal charge carriers in CdTe and extract values for the expected charge sharing depending on the impact point and bias voltage. The results on charge sharing obtained with COMSOL are combined with GAMOS, a Geant based particle tracking Monte Carlo software package, to get a full evaluation of the amount of charge sharing in pixelated CdTe for different gamma impact points.

  13. Simulation of single-event energy-deposition spreading in a hybrid pixellated detector for γ imaging

    NASA Astrophysics Data System (ADS)

    Manach, Erwan; Gal, Olivier

    2002-07-01

    In the framework of the Medipix2 Collaboration, a new photon-counting chip is being developed made of a 256×256 array of 55 μm-side square pixels. Although the chip was primarily developed for semiconductor X-ray imagers, we think that this type of device could be used in applications such as decommissioning of nuclear facilities where typical sources have γ-ray energies in the range of a few hundred keV. In order to enhance the detection efficiency in this energy range, we envisage connecting the Medipix2 chip to a CdTe or CdZnTe substrate (at least 1 mm thick). The small pixel size, the thickness of the Cd(Zn)Te substrate and the high photon energy motivate us to estimate first the spatial energy spreading following a photon interaction inside the detector. Estimations were made using the MCNP Monte Carlo package by simulating the individual energy distribution for each primary photon interaction. As an illustration of our results, simulating a 660 keV γ source, we found that there are two pixels on average, for each primary interaction, on which the deposited energy exceeds 50 keV. We have also made more accurate simulations using sub-pixels of side 11 μm, in order to evaluate the distance between the barycentre of the deposited energy and the photon impact point. As an example, with a 660 keV γ source, we found that the average of this distance reaches 67 μm when restricted to the events depositing more than 400 keV. If all events are taken into account, the mean distance is 26 μm, even though there is a small proportion of interactions where the scattered photon interacts somewhere else in the detector. Results are presented for different photon energies (60 keV, 660 keV, 1.25 MeV) and different materials (CdTe, GaAs).

  14. An XPS study of bromine in methanol etching and hydrogen peroxide passivation treatments for cadmium zinc telluride radiation detectors

    NASA Astrophysics Data System (ADS)

    Babar, S.; Sellin, P. J.; Watts, J. F.; Baker, M. A.

    2013-01-01

    The performance of single crystal CdZnTe radiation detectors is dependent on both the bulk and the surface properties of the material. After single crystal fabrication and mechanical polishing, modification of the surface to remove damage and reduce the surface leakage current is generally achieved through chemical etching followed by a passivation treatment. In this work, CdZnTe single crystals have been chemically etched using a bromine in methanol (BM) treatment. The BM concentrations employed were 0.2 and 2.0 (v/v) % and exposure times varied between 5 and 120 s. Angle resolved XPS and sputter depth profiling has been employed to characterize the surfaces for the different exposure conditions. A Te rich surface layer was formed for all exposures and the layer thickness was found to be independent of exposure time. The enriched Te layer thickness was accurately determined by calibrating the sputter rate against a CdTe layer of known thickness. For BM concentrations of 0.2 (v/v) % and 2 (v/v) %, the Te layer thickness was determined to be 1.3 ± 0.2 and 1.8 ± 0.2 nm, respectively. The BM etched surfaces have subsequently been passivated in a 30 wt.% H2O2 solution employing exposure time of 15 s. The oxide layer thickness has been calculated using two standard XPS methodologies, based on the Beer-Lambert expression. The TeO2 thickness calculated from ARXPS data are slightly higher than the thickness obtained by the simplified Beer-Lambert expression. For BM exposures of 30-120 s followed by a passivation treatment of 30 wt. % H2O2 solution employing an exposure time 15 s, the ARXPS method gave an average TeO2 thickness value of 1.20 nm and the simplified Beer-Lambert expression gave an average thickness value of 0.99 nm.

  15. SU-E-T-231: Measurements of Gold Nanoparticle-Mediated Proton Dose Enhancement Due to Particle-Induced X-Ray Emission and Activation Products Using Radiochromic Films and CdTe Detector

    SciTech Connect

    Cho, J; Cho, S; Manohar, N; Krishnan, S

    2014-06-01

    Purpose: There have been several reports of enhanced cell-killing and tumor regression when tumor cells and mouse tumors were loaded with gold nanoparticles (GNPs) prior to proton irradiation. While particle-induced xray emission (PIXE), Auger electrons, secondary electrons, free radicals, and biological effects have been suggested as potential mechanisms responsible for the observed GNP-mediated dose enhancement/radiosensitization, there is a lack of quantitative analysis regarding the contribution from each mechanism. Here, we report our experimental effort to quantify some of these effects. Methods: 5-cm-long cylindrical plastic vials were filled with 1.8 mL of either water or water mixed with cylindrical GNPs at the same gold concentration (0.3 mg Au/g) as used in previous animal studies. A piece of EBT2 radiochromic film (30-µm active-layer sandwiched between 80/175-µm outer-layers) was inserted along the long axis of each vial and used to measure dose enhancement due to PIXE from GNPs. Vials were placed at center-of-modulation (COM) and 3-cm up-/down-stream from COM and irradiated with 5 different doses (2–10 Gy) using 10-cm-SOBP 160-MeV protons. After irradiation, films were cleaned and read to determine the delivered dose. A vial containing spherical GNPs (20 mg Au/g) was also irradiated, and gamma-rays from activation products were measured using a cadmium-telluride (CdTe) detector. Results: Film measurements showed no significant dose enhancement beyond the experimental uncertainty (∼2%). There was a detectable activation product from GNPs, but it appeared to contribute to dose enhancement minimally (<0.01%). Conclusion: Considering the composition of EBT2 film, it can be inferred that gold characteristic x-rays from PIXE and their secondary electrons make insignificant contribution to dose enhancement. The current investigation also suggests negligible dose enhancement due to activation products. Thus, previously-reported GNP-mediated proton dose

  16. Development activities of a CdTe/CdZnTe pixel detector for gamma-ray spectrometry with imaging and polarimetry capability in astrophysics

    NASA Astrophysics Data System (ADS)

    Gálvez, J. L.; Hernanz, M.; Álvarez, J. M.; Álvarez, L.; La Torre, M.; Caroli, E.; Lozano, M.; Pellegrini, G.; Ullán, M.; Cabruja, E.; Martínez, R.; Chmeissani, M.; Puigdengoles, C.

    2013-05-01

    In the last few years we have been working on feasibility studies of future instruments in the gamma-ray range, from several keV up to a few MeV, in collaboration with other research institutes. High sensitivities are essential to perform detailed studies of cosmic explosions and cosmic accelerators, e.g., Supernovae, Classical Novae, Supernova Remnants (SNRs), Gamma-Ray Bursts (GRBs), Pulsars, Active Galactic Nuclei (AGN).Cadmium Telluride (CdTe) and Cadmium Zinc Telluride (CdZnTe) are very attractive materials for gamma-ray detection, since they have already demonstrated their great performance onboard current space missions, such as IBIS/INTEGRAL and BAT/SWIFT, and future projects like ASIM onboard the ISS. However, the energy coverage of these instruments is limited up to a few hundred keV, and there has not been yet a dedicated instrument for polarimetry.Our research and development activities aim to study a gamma-ray imaging spectrometer in the MeV range based on CdTe detectors, suited either for the focal plane of a focusing mission or as a calorimeter for a Compton camera. In addition, our undergoing detector design is proposed as the baseline for the payload of a balloon-borne experiment dedicated to hard X- and soft gamma-ray polarimetry, currently under study and called CμSP (CZT μ-Spectrometer Polarimeter). Other research institutes such as INAF-IASF, DTU Space, LIP, INEM/CNR, CEA, are involved in this proposal. We will report on the main features of the prototype we are developing at the Institute of Space Sciences, a gamma-ray detector with imaging and polarimetry capabilities in order to fulfil the combined requirement of high detection efficiency with good spatial and energy resolution driven by the science.

  17. X-ray Topography to Characterize Surface Damage on CdZnTe Crystals

    SciTech Connect

    Black, David; Woicik, Joseph; Duff, Martine C.; Hunter, Douglas B.; Burger, Arnold; Groza, Michael

    2008-12-05

    Synthetic CdZnTe or 'CZT' crystals can be used for room temperature detection of {gamma}-radiation. Structural/morphological heterogeneities within CZT, such as twinning, secondary phases (often referred to as inclusions or precipitates), and poly-crystallinity can affect detector performance. As part of a broader study using synchrotron radiation techniques to correlate detector performance to microstructure, x-ray topography (XRT) has been used to characterize CZT crystals. We have found that CZT crystals almost always have a variety of residual surface damage, which interferes with our ability to observe the underlying microstructure for purposes of crystal quality evaluation. Specific structures are identifiable as resulting from fabrication processes and from handling and shipping of sample crystals. Etching was found to remove this damage; however, our studies have shown that the radiation detector performance of the etched surfaces was inferior to the as-polished surface due to higher surface currents which result in more peak tailing and less energy resolution. We have not fully investigated the effects of the various types of inducible damage on radiation detector performance.

  18. X-ray Topography to Characterize Surface Damage on CdZnTe Crystals

    SciTech Connect

    Black, David; Woicik, Joseph; Duff, Martine C.; Hunter, Douglas B.; Burger, Arnold; Groza, Michael

    2008-07-01

    Synthetic CdZnTe or 'CZT' crystals can be used for room temperature detection of {gamma}-radiation. Structural/morphological heterogeneities within CZT, such as twinning, secondary phases (often referred to as inclusions or precipitates), and poly-crystallinity can affect detector performance. As part of a broader study using synchrotron radiation techniques to correlate detector performance to microstructure, x-ray topography (XRT) has been used to characterize CZT crystals. We have found that CZT crystals almost always have a variety of residual surface damage, which interferes with our ability to observe the underlying microstructure for purposes of crystal quality evaluation. Specific structures are identifiable as resulting from fabrication processes and from handling and shipping of sample crystals. Etching was found to remove this damage; however, our studies have shown that the radiation detector performance of the etched surfaces was inferior to the as-polished surface due to higher surface currents which result in more peak tailing and less energy resolution. We have not fully investigated the effects of the various types of inducible damage on radiation detector performance. (authors)

  19. Correlation Between Bulk Material Defects and Spectroscopic Response in Cadmium Zinc Telluride Detectors

    NASA Technical Reports Server (NTRS)

    Parker, Bradford H.; Stahle, C. M.; Barthelmy, S. D.; Parsons, A. M.; Tueller, J.; VanSant, J. T.; Munoz, B. F.; Snodgrass, S. J.; Mullinix, R. E.

    1999-01-01

    One of the critical challenges for large area cadmium zinc telluride (CdZnTe) detector arrays is obtaining material capable of uniform imaging and spectroscopic response. Two complementary nondestructive techniques for characterizing bulk CdZnTe have been developed to identify material with a uniform response. The first technique, infrared transmission imaging, allows for rapid visualization of bulk defects. The second technique, x-ray spectral mapping, provides a map of the material spectroscopic response when it is configured as a planar detector. The two techniques have been used to develop a correlation between bulk defect type and detector performance. The correlation allows for the use of infrared imaging to rapidly develop wafer mining maps. The mining of material free of detrimental defects has the potential to dramatically increase the yield and quality of large area CdZnTe detector arrays.

  20. Results of a Si/Cdte Compton Telescope

    SciTech Connect

    Oonuki, Kousuke; Tanaka, Takaaki; Watanabe, Shin; Takeda, Shin'ichiro; Nakazawa, Kazuhiro; Mitani, Takefumi; Takahashi, Tadayuki; Tajima, Hiroyasu; Fukazawa, Yasushi; Nomachi, Masaharu; /Sagamihara, Inst. Space Astron. Sci. /Tokyo U. /SLAC /Hiroshima U. /Osaka U.

    2005-09-23

    We have been developing a semiconductor Compton telescope to explore the universe in the energy band from several tens of keV to a few MeV. We use a Si strip and CdTe pixel detector for the Compton telescope to cover an energy range from 60 keV. For energies above several hundred keV, the higher efficiency of CdTe semiconductor in comparison with Si is expected to play an important role as an absorber and a scatterer. In order to demonstrate the spectral and imaging capability of a CdTe-based Compton Telescope, we have developed a Compton telescope consisting of a stack of CdTe pixel detectors as a small scale prototype. With this prototype, we succeeded in reconstructing images and spectra by solving the Compton equation from 122 keV to 662 keV. The energy resolution (FWHM) of reconstructed spectra is 7.3 keV at 511 keV and 3.1 keV at 122 keV, respectively. The angular resolution obtained at 511 keV is measured to be 12.2{sup o}(FWHM).

  1. Ionizing Radiation Detector

    DOEpatents

    Wright, Gomez W.; James, Ralph B.; Burger, Arnold; Chinn, Douglas A.

    2003-11-18

    A CdZnTe (CZT) crystal provided with a native CdO dielectric coating to reduce surface leakage currents and thereby, improve the resolution of instruments incorporating detectors using CZT crystals is disclosed. A two step process is provided for forming the dielectric coating which includes etching the surface of a CZT crystal with a solution of the conventional bromine/methanol etch treatment, and passivating the CZT crystal surface with a solution of 10 w/o NH.sub.4 F and 10 w/o H.sub.2 O.sub.2 in water after attaching electrical contacts to the crystal surface.

  2. Edge effects in a small pixel CdTe for X-ray imaging

    NASA Astrophysics Data System (ADS)

    Duarte, D. D.; Bell, S. J.; Lipp, J.; Schneider, A.; Seller, P.; Veale, M. C.; Wilson, M. D.; Baker, M. A.; Sellin, P. J.; Kachkanov, V.; Sawhney, K. J. S.

    2013-10-01

    Large area detectors capable of operating with high detection efficiency at energies above 30 keV are required in many contemporary X-ray imaging applications. The properties of high Z compound semiconductors, such as CdTe, make them ideally suitable to these applications. The STFC Rutherford Appleton Laboratory has developed a small pixel CdTe detector with 80 × 80 pixels on a 250 μm pitch. Historically, these detectors have included a 200 μm wide guard band around the pixelated anode to reduce the effect of defects in the crystal edge. The latest version of the detector ASIC is capable of four-side butting that allows the tiling of N × N flat panel arrays. To limit the dead space between modules to the width of one pixel, edgeless detector geometries have been developed where the active volume of the detector extends to the physical edge of the crystal. The spectroscopic performance of an edgeless CdTe detector bump bonded to the HEXITEC ASIC was tested with sealed radiation sources and compared with a monochromatic X-ray micro-beam mapping measurements made at the Diamond Light Source, U.K. The average energy resolution at 59.54 keV of bulk and edge pixels was 1.23 keV and 1.58 keV, respectively. 87% of the edge pixels present fully spectroscopic performance demonstrating that edgeless CdTe detectors are a promising technology for the production of large panel radiation detectors for X-ray imaging.

  3. Impurity Gettering Effect of Te Inclusions in Cdznte Single Crystals

    SciTech Connect

    Yang, G.; Bolotnikov, A; Cui, Y; Camarda, G; Hossain, A; James, R

    2009-01-01

    The local impurity distribution in Te inclusions of CdZnTe (CZT) crystal was investigated by the time-of-flight secondary ion mass spectrometry (Tof-SIMS) technique. Direct evidence of impurity gettering in Te inclusions has been observed for the first time. The impurity gettering in Te inclusions originated from the diffusion mechanism during crystal growth and segregation mechanism during crystal cooling. This phenomenon is meaningful, because it reveals how Te inclusions affect CZT properties and provides a possible approach to reduce the impurities in CZT by the way of removing Te inclusions.

  4. Simulation and Comparison of Various Gamma-Ray Imaging Detector Configurations for IPRL Devices

    SciTech Connect

    Manini, H A

    2006-12-27

    Simulations are performed for seven different geometrical configurations of CdZnTe (CZT) detector arrays for Intelligent Personal Radiation Locator (IPRL) devices. IPRL devices are portable radiation detectors that have gamma-ray imaging capability. The detector performance is analyzed for each type of IPRL configuration, and the intrinsic photopeak efficiency, intrinsic photopeak count rate, detector image resolution, imaging efficiency, and imaging count rate are determined.

  5. CdTe devices and method of manufacturing same

    SciTech Connect

    Gessert, Timothy A.; Noufi, Rommel; Dhere, Ramesh G.; Albin, David S.; Barnes, Teresa; Burst, James; Duenow, Joel N.; Reese, Matthew

    2015-09-29

    A method of producing polycrystalline CdTe materials and devices that incorporate the polycrystalline CdTe materials are provided. In particular, a method of producing polycrystalline p-doped CdTe thin films for use in CdTe solar cells in which the CdTe thin films possess enhanced acceptor densities and minority carrier lifetimes, resulting in enhanced efficiency of the solar cells containing the CdTe material are provided.

  6. PHOTOINDUCED CURRENTS IN CDZNTE CRYSTALS AS A FUNCTION OF ILLUMINATION WAVELENGTH

    SciTech Connect

    Teague, L.; Washington, A.; Duff, M.

    2012-04-23

    We report variations in the currents of CdZnTe semiconductor crystals during exposure to a series of light emitting diodes of various wavelengths ranging from 470 to 950 nm. The changes in the steady-state current of one CdZnTe crystal with and without illumination along with the time dependence of the illumination effects are discussed. Analysis of the de-trapping and transient bulk currents during and after optical excitation yield insight into the behaviour of charge traps within the crystal. Similar behaviour is observed for illumination of a second CdZnTe crystal suggesting that the overall illumination effects are not crystal dependent.

  7. Applications of CdTe to nuclear medicine. Annual report, February 1, 1979-January 31, 1980

    SciTech Connect

    Entine, G

    1980-01-01

    The application of CdTe gamma detectors in nuclear medicine is reported on. An internal probe was developed which can be inserted into the heart to measure the efficiency of various radiopharmaceuticals in the treatment of heart attacks. A second application is an array of detectors which is light enough to be worn by ambulatory patients and can measure the change in cardiac output over an eight hour period during heart attack treatment. The instrument includes an on board tape recorder. (ACR)

  8. Evaluation of a multistage CdZnTe Compton camera for prompt γ imaging for proton therapy

    NASA Astrophysics Data System (ADS)

    McCleskey, M.; Kaye, W.; Mackin, D. S.; Beddar, S.; He, Z.; Polf, J. C.

    2015-06-01

    A new detector system, Polaris J from H3D, has been evaluated for its potential application as a Compton camera (CC) imaging device for prompt γ rays (PGs) emitted during proton radiation therapy (RT) for the purpose of dose range verification. This detector system consists of four independent CdZnTe detector stages and a coincidence module, allowing the user to construct a Compton camera in different geometrical configurations and to accept both double and triple scatter events. Energy resolution for the 662 keV line from 137Cs was found to be 9.7 keV FWHM. The raw absolute efficiencies for double and triple scatter events were 2.2 ×10-5 and 5.8 ×10-7, respectively, for γs from a 60Co source. The position resolution for the reconstruction of a point source from the measured CC data was about 2 mm. Overall, due to the low efficiency of the Polaris J CC, the current system was deemed not viable for imaging PGs emitted during proton RT treatment delivery. However, using a validated Monte Carlo model of the CC, we found that by increasing the size of the detectors and placing them in a two stage configuration, the efficiency could be increased to a level to make PG imaging possible during proton RT.

  9. Simulation-based evaluation and optimization of a new CdZnTe gamma-camera architecture (HiSens)

    NASA Astrophysics Data System (ADS)

    Robert, Charlotte; Montémont, Guillaume; Rebuffel, Véronique; Buvat, Irène; Guérin, Lucie; Verger, Loïck

    2010-05-01

    A new gamma-camera architecture named HiSens is presented and evaluated. It consists of a parallel hole collimator, a pixelated CdZnTe (CZT) detector associated with specific electronics for 3D localization and dedicated reconstruction algorithms. To gain in efficiency, a high aperture collimator is used. The spatial resolution is preserved thanks to accurate 3D localization of the interactions inside the detector based on a fine sampling of the CZT detector and on the depth of interaction information. The performance of this architecture is characterized using Monte Carlo simulations in both planar and tomographic modes. Detective quantum efficiency (DQE) computations are then used to optimize the collimator aperture. In planar mode, the simulations show that the fine CZT detector pixelization increases the system sensitivity by 2 compared to a standard Anger camera without loss in spatial resolution. These results are then validated against experimental data. In SPECT, Monte Carlo simulations confirm the merits of the HiSens architecture observed in planar imaging.

  10. Selective CdTe Nanoheteroepitaxial Growth on Si(100) Substrates Using the Close-Spaced Sublimation Technique Without the Use of a Mask

    NASA Astrophysics Data System (ADS)

    Diaz, A.; Quinones, S. A.; Ferrer, D. A.

    2013-06-01

    The development of HgCdTe detectors requires high sensitivity, small pixel size, low defect density, long-term thermal-cycling reliability, and large-area substrates. CdTe bulk substrates were initially used for epitaxial growth of HgCdTe films. However, CdTe has a lattice mismatch with long-wavelength infrared (LWIR) and middle-wavelength infrared (MWIR) HgCdTe that results in detrimental dislocation densities above mid-106 cm-2. This work explores the use of CdTe/Si as a possible substrate for HgCdTe detectors. Although there is a 19% lattice mismatch between CdTe and Si, the nanoheteroepitaxy (NHE) technique makes it possible to grow CdTe on Si substrates with fewer defects at the CdTe/Si interface. In this work, Si(100) was patterned using photolithography and dry etching to create 500-nm to 1- μm pillars. CdTe was selectively deposited on the pillar surfaces using the close-spaced sublimation (CSS) technique. Scanning electron microscopy (SEM) was used to characterize the CdTe selective growth and grain morphology, and transmission electron microscopy (TEM) was used to analyze the structure and quality of the grains. CdTe selectivity was achieved for most of the substrate and source temperatures used in this study. The ability to selectively deposit CdTe on patterned Si(100) substrates without the use of a mask or seed layer has not been observed before using the CSS technique. The results from this study confirm that CSS has the potential to be an effective and low-cost technique for selective nanoheteroepitaxial growth of CdTe films on Si(100) substrates for infrared detector applications.

  11. High-resolution ionization detector and array of such detectors

    DOEpatents

    McGregor, Douglas S.; Rojeski, Ronald A.

    2001-01-16

    A high-resolution ionization detector and an array of such detectors are described which utilize a reference pattern of conductive or semiconductive material to form interaction, pervious and measurement regions in an ionization substrate of, for example, CdZnTe material. The ionization detector is a room temperature semiconductor radiation detector. Various geometries of such a detector and an array of such detectors produce room temperature operated gamma ray spectrometers with relatively high resolution. For example, a 1 cm.sup.3 detector is capable of measuring .sup.137 Cs 662 keV gamma rays with room temperature energy resolution approaching 2% at FWHM. Two major types of such detectors include a parallel strip semiconductor Frisch grid detector and the geometrically weighted trapezoid prism semiconductor Frisch grid detector. The geometrically weighted detector records room temperature (24.degree. C.) energy resolutions of 2.68% FWHM for .sup.137 Cs 662 keV gamma rays and 2.45% FWHM for .sup.60 Co 1.332 MeV gamma rays. The detectors perform well without any electronic pulse rejection, correction or compensation techniques. The devices operate at room temperature with simple commercially available NIM bin electronics and do not require special preamplifiers or cooling stages for good spectroscopic results.

  12. Recent developments in semiconductor gamma-ray detectors

    SciTech Connect

    Luke, Paul N.; Amman, Mark; Tindall, Craig; Lee, Julie S.

    2003-10-28

    The successful development of lithium-drifted Ge detectors in the 1960's marked the beginning of the significant use of semiconductor crystals for direct detection and spectroscopy of gamma rays. In the 1970's, high-purity Ge became available, which enabled the production of complex detectors and multi-detector systems. In the following decades, the technology of semiconductor gamma-ray detectors continued to advance, with significant developments not only in Ge detectors but also in Si detectors and room-temperature compound-semiconductor detectors. In recent years, our group at Lawrence Berkeley National Laboratory has developed a variety of gamma ray detectors based on these semiconductor materials. Examples include Ge strip detectors, lithium-drifted Si strip detectors, and coplanar-grid CdZnTe detectors. These advances provide new capabilities in the measurement of gamma rays, such as the ability to perform imaging and the realization of highly compact spectroscopy systems.

  13. As-Received CdZnTe Substrate Contamination

    NASA Astrophysics Data System (ADS)

    Benson, J. D.; Bubulac, L. O.; Jaime-Vasquez, M.; Lennon, C. M.; Smith, P. J.; Jacobs, R. N.; Markunas, J. K.; Almeida, L. A.; Stoltz, A.; Arias, J. M.; Wijewarnasuriya, P. S.; Peterson, J.; Reddy, M.; Vilela, M. F.; Johnson, S. M.; Lofgreen, D. D.; Yulius, A.; Carmody, M.; Hirsch, R.; Fiala, J.; Motakef, S.

    2015-09-01

    State-of-the-art as-received (112)B CdZnTe substrates were examined for surface impurity contamination, polishing damage, and tellurium precipitates/inclusions. A maximum surface impurity concentration of Al = 7.5 × 1014, Si = 3.7 × 1013, Cl = 3.12 × 1015, S = 1.7 × 1014, P = 7.1 × 1013, Fe = 1.0 × 1013, Br = 1.9 × 1012, and Cu = 4 × 1012 atoms cm-2 was observed on an as-received 6 × 6 cm wafer. As-received CdZnTe substrates have scratches and residual polishing grit on the (112)B surface. Polishing scratches are 0.3 nm in depth and 0.1 μm wide. The polishing grit density was observed to vary from wafer-to-wafer from ˜5 × 106 to 2 × 108 cm-2. Te precipitate/inclusion size and density was determined by near-infrared automated microscopy. A Te precipitate/inclusion diameter histogram was obtained for the near-surface (top ~140 μm) of a 6 × 6 cm substrate. The average areal Te precipitate/inclusion density was observed to be fairly uniform. However, there was a large density of Te precipitates/inclusions with a diameter significantly greater than the mean. Te precipitate/inclusion density >10 μm diameter = 2.8 × 103 cm-3. The large Te precipitates/inclusions are laterally non-uniformly distributed across the wafer.

  14. CdTe quantum dots for an application in the life sciences

    NASA Astrophysics Data System (ADS)

    Thi Dieu Thuy, Ung; Toan, Pham Song; Chi, Tran Thi Kim; Duy Khang, Dinh; Quang Liem, Nguyen

    2010-12-01

    This report highlights the results of the preparation of semiconductor CdTe quantum dots (QDs) in the aqueous phase. The small size of a few nm and a very high luminescence quantum yield exceeding 60% of these materials make them promisingly applicable to bio-medicine labeling. Their strong, two-photon excitation luminescence is also a good characteristic for biolabeling without interference with the cell fluorescence. The primary results for the pH-sensitive CdTe QDs are presented in that fluorescence of CdTe QDs was used as a proton sensor to detect proton flux driven by adenosine triphosphate (ATP) synthesis in chromatophores. In other words, these QDs could work as pH-sensitive detectors. Therefore, the system of CdTe QDs on chromatophores prepared from the cells of Rhodospirillum rubrum and the antibodies against the beta-subunit of F0F1-ATPase could be a sensitive detector for the avian influenza virus subtype A/H5N1.

  15. Extended defects in as-grown CdZnTe

    SciTech Connect

    Xu, L.; Bolotnikov, A.E.; Hossain, A.; Kim, K-H.; Gul, R.; Yang, G.; Camarda, G.S.; Marchini, L.; Cui, Y.; James, R.B.; Xu, Y.; Wang, T.; Jie, W.

    2010-08-01

    We characterized samples cut from different locations in as-grown CdZnTe (CZT) ingots, using Automated Infrared (IR) Transmission Microscopy and White Beam X-ray Diffraction Topography (WBXDT), to locate and identify the extended defects in them. Our goal was to define the distribution of these defects throughout the entire ingot and their effects on detectors’ performance as revealed by the pulse-height spectrum. We found the highest- and the lowest- concentration of Te inclusions, respectively, in the head and middle part of the ingot, which could serve as guidance in selecting samples. Crystals with high concentration of Te inclusions showed high leakage current and poor performance, because the accumulated charge loss around trapping centers associated with Te inclusions distorts the internal electric field, affects the carrier transport properties inside the crystal, and finally degrades the detector’s performance. In addition, other extended defects revealed by the WBXDT measurements severely reduced the detector’s performance, since they trap large numbers of electrons, leading to a low signal for the pulse-height spectrum, or none whatsoever. Finally, we fully correlated the detector’s performance with our information on the extended defects gained from both the IR- and the WBXDT-measurements.

  16. Characterization of Pixelated Cadmium-Zinc-Telluride Detectors for Astrophysical Applications

    NASA Technical Reports Server (NTRS)

    Gaskin, Jessica; Sharma, Dharma; Ramsey, Brian; Seller, Paul

    2003-01-01

    Comparisons of charge sharing and charge loss measurements between two pixelated Cadmium-Zinc-Telluride (CdZnTe) detectors are discussed. These properties along with the detector geometry help to define the limiting energy resolution and spatial resolution of the detector in question. The first detector consists of a 1-mm-thick piece of CdZnTe sputtered with a 4x4 array of pixels with pixel pitch of 750 microns (inter-pixel gap is 100 microns). Signal readout is via discrete ultra-low-noise preamplifiers, one for each of the 16 pixels. The second detector consists of a 2-mm-thick piece of CdZnTe sputtered with a 16x16 array of pixels with a pixel pitch of 300 microns (inter-pixel gap is 50 microns). This crystal is bonded to a custom-built readout chip (ASIC) providing all front-end electronics to each of the 256 independent pixels. These detectors act as precursors to that which will be used at the focal plane of the High Energy Replicated Optics (HERO) telescope currently being developed at Marshall Space Flight Center. With a telescope focal length of 6 meters, the detector needs to have a spatial resolution of around 200 microns in order to take full advantage of the HERO angular resolution. We discuss to what degree charge sharing will degrade energy resolution but will improve our spatial resolution through position interpolation.

  17. Evaluation of the efficiency curve of a Cadmiun Telluride detector for low-energy photon spectrometry.

    PubMed

    Correia, Amanda Ribeiro; Iwahara, Akira; da Cruz, Paulo Alberto Lima; da Silva, Carlos José; Tauhata, Luiz; Poledna, Roberto; da Silva, Ronaldo Lins; de Queiroz Filho, Pedro Pacheco; Lopes, Ricardo Tadeu

    2016-10-01

    The performance of a Cadmiun Telluride (CdTe) detector for low energy photon spectrometry was evaluated. Collected data were analyzed using the basic software package available with the CdTe detector system and the COLEGRAM code developed for photopeak deconvolution at LNHB/France. Several calibrated point sources were used to determine the energy versus efficiency curve. The efficiency curve was used in the determination of main X-ray intensities of (153)Sm and (177)Lu.

  18. Evaluation of the efficiency curve of a Cadmiun Telluride detector for low-energy photon spectrometry.

    PubMed

    Correia, Amanda Ribeiro; Iwahara, Akira; da Cruz, Paulo Alberto Lima; da Silva, Carlos José; Tauhata, Luiz; Poledna, Roberto; da Silva, Ronaldo Lins; de Queiroz Filho, Pedro Pacheco; Lopes, Ricardo Tadeu

    2016-10-01

    The performance of a Cadmiun Telluride (CdTe) detector for low energy photon spectrometry was evaluated. Collected data were analyzed using the basic software package available with the CdTe detector system and the COLEGRAM code developed for photopeak deconvolution at LNHB/France. Several calibrated point sources were used to determine the energy versus efficiency curve. The efficiency curve was used in the determination of main X-ray intensities of (153)Sm and (177)Lu. PMID:27544313

  19. Growth and analysis of micro and nano CdTe arrays for solar cell applications

    NASA Astrophysics Data System (ADS)

    Aguirre, Brandon Adrian

    CdTe is an excellent material for infrared detectors and photovoltaic applications. The efficiency of CdTe/CdS solar cells has increased very rapidly in the last 3 years to ˜20% but is still below the maximum theoretical value of 30%. Although the short-circuit current density is close to its maximum of 30 mA/cm2, the open circuit voltage has potential to be increased further to over 1 Volt. The main limitation that prevents further increase in the open-circuit voltage and therefore efficiency is the high defect density in the CdTe absorber layer. Reducing the defect density will increase the open-circuit voltage above 1 V through an increase in the carrier lifetime and concentration to tau >10 ns and p > 10 16 cm-3, respectively. However, the large lattice mismatch (10%) between CdTe and CdS and the polycrystalline nature of the CdTe film are the fundamental reasons for the high defect density and pose a difficult challenge to solve. In this work, a method to physically and electrically isolate the different kinds of defects at the nanoscale and understand their effect on the electrical performance of CdTe is presented. A SiO2 template with arrays of window openings was deposited between the CdTe and CdS to achieve selective-area growth of the CdTe via close-space sublimation. The diameter of the window openings was varied from the micro to the nanoscale to study the effect of size on nucleation, grain growth, and defect density. The resulting structures enabled the possibility to electrically isolate and individually probe micrometer and nanoscale sized CdTe/CdS cells. Electron back-scattered diffraction was used to observe grain orientation and defects in the miniature cells. Scanning and transmission electron microscopy was used to study the morphology, grain boundaries, grain orientation, defect structure, and strain in the layers. Finally, conducting atomic force microscopy was used to study the current-voltage characteristics of the solar cells. An

  20. CdTe quantum dots@luminol as signal amplification system for chrysoidine with chemiluminescence-chitosan/graphene oxide-magnetite-molecularly imprinting sensor

    NASA Astrophysics Data System (ADS)

    Duan, Huimin; Li, Leilei; Wang, Xiaojiao; Wang, Yanhui; Li, Jianbo; Luo, Chuannan

    2016-01-01

    A sensitive chemiluminescence (CL) sensor based on chemiluminescence resonance energy transfer (CRET) in CdTe quantum dots@luminol (CdTe QDs@luminol) nanomaterials combined with chitosan/graphene oxide-magnetite-molecularly imprinted polymer (Cs/GM-MIP) for sensing chrysoidine was developed. CdTe QDs@luminol was designed to not only amplify the signal of CL but also reduce luminol consumption in the detection of chrysoidine. On the basis of the abundant hydroxy and amino, Cs and graphene oxide were introduced into the GM-MIP to improve the adsorption ability. The adsorption capacities of chrysoidine by both Cs/GM-MIP and non-imprinted polymer (Cs/GM-NIP) were investigated, and the CdTe QDs@luminol and Cs/GM-MIP were characterized by UV-vis, FTIR, SEM and TEM. The proposed sensor can detect chrysoidine within a linear range of 1.0 × 10- 7 - 1.0 × 10- 5 mol/L with a detection limit of 3.2 × 10- 8 mol/L (3δ) due to considerable chemiluminescence signal enhancement of the CdTe quantum dots@luminol detector and the high selectivity of the Cs/GM-MIP system. Under the optimal conditions of CL, the CdTe QDs@luminol-Cs/GM-MIP-CL sensor was used for chrysoidine determination in samples with satisfactory recoveries in the range of 90-107%.

  1. CdTe quantum dots@luminol as signal amplification system for chrysoidine with chemiluminescence-chitosan/graphene oxide-magnetite-molecularly imprinting sensor.

    PubMed

    Duan, Huimin; Li, Leilei; Wang, Xiaojiao; Wang, Yanhui; Li, Jianbo; Luo, Chuannan

    2016-01-15

    A sensitive chemiluminescence (CL) sensor based on chemiluminescence resonance energy transfer (CRET) in CdTe quantum dots@luminol (CdTe QDs@luminol) nanomaterials combined with chitosan/graphene oxide-magnetite-molecularly imprinted polymer (Cs/GM-MIP) for sensing chrysoidine was developed. CdTe QDs@luminol was designed to not only amplify the signal of CL but also reduce luminol consumption in the detection of chrysoidine. On the basis of the abundant hydroxy and amino, Cs and graphene oxide were introduced into the GM-MIP to improve the adsorption ability. The adsorption capacities of chrysoidine by both Cs/GM-MIP and non-imprinted polymer (Cs/GM-NIP) were investigated, and the CdTe QDs@luminol and Cs/GM-MIP were characterized by UV-vis, FTIR, SEM and TEM. The proposed sensor can detect chrysoidine within a linear range of 1.0×10(-7) - 1.0×10(-5) mol/L with a detection limit of 3.2×10(-8) mol/L (3δ) due to considerable chemiluminescence signal enhancement of the CdTe quantum dots@luminol detector and the high selectivity of the Cs/GM-MIP system. Under the optimal conditions of CL, the CdTe QDs@luminol-Cs/GM-MIP-CL sensor was used for chrysoidine determination in samples with satisfactory recoveries in the range of 90-107%.

  2. The microstructure, optical and electrical property of CdZnTe thick films grown from a CSS method

    NASA Astrophysics Data System (ADS)

    Zhang, Yuelu; Wang, Linjun; Xu, Run; Huang, Jian; Meng, Hua; Tao, Jun; Zhang, Jijun; Min, Jiahua; Shen, Yue

    2015-12-01

    Polycrystalline CdZnTe thick films with an average grain size of 30 μm and thickness of 270 μm were successfully grown on SnO2:F (FTO)-coated glass substrates by close-spaced sublimation method. Electrical properties and UV response of CdZnTe thick films after Br-MeOH etching and ZnCl2 annealing treatment were investigated. By means of the photo-current measurements, the value of mobility-lifetime (μτ) products for CdZnTe films were firstly reported. The results showed that Br-MeOH etching significantly improved UV detection sensitivity of CdZnTe thick films, and made the surface distribution of UV sensitivity more homogeneous. It was also found that a ZnCl2 annealing process did not improve the electrical properties.

  3. The Underwater Spectrometric System Based on CZT Detector for Survey of the Bottom of MR Reactor Pool - 13461

    SciTech Connect

    Potapov, Victor; Safronov, Alexey; Ivanov, Oleg; Smirnov, Sergey; Stepanov, Vyacheslav

    2013-07-01

    The underwater spectrometer system for detection of irradiated nuclear fuel on the pool bottom of the reactor was elaborated. During the development process metrological studies of CdZnTe (CZT) detectors were conducted. These detectors are designed for spectrometric measurements in high radiation fields. A mathematical model based on the Monte Carlo method was created to evaluate the capability of such a system. A few experimental models were realized and the characteristics of the spectrometric system are represented. (authors)

  4. Thermodynamics of post-growth annealing of cadmium zinc telluride nuclear radiation detectors

    NASA Astrophysics Data System (ADS)

    Adams, Aaron Lee

    Nuclear Radiation Detectors are used for detecting, tracking, and identifying radioactive materials which emit high-energy gamma and X-rays. The use of Cadmium Zinc Telluride (CdZnTe) detectors is particularly attractive because of the detector's ability to operate at room temperature and measure the energy spectra of gamma-ray sources with a high resolution, typically less than 1% at 662 keV. While CdZnTe detectors are acceptable imperfections in the crystals limit their full market potential. One of the major imperfections are Tellurium inclusions generated during the crystal growth process by the retrograde solubility of Tellurium and Tellurium-rich melt trapped at the growth interface. Tellurium inclusions trap charge carriers generated by gamma and X-ray photons and thus reduce the portion of generated charge carriers that reach the electrodes for collection and conversion into a readable signal which is representative of the ionizing radiation's energy and intensity. One approach in resolving this problem is post-growth annealing which has the potential of removing the Tellurium inclusions and associated impurities. The goal of this project is to use experimental techniques to study the thermodynamics of Tellurium inclusion migration in post-growth annealing of CdZnTe nuclear detectors with the temperature gradient zone migration (TGZM) technique. Systematic experiments will be carried out to provide adequate thermodynamic data that will inform the engineering community of the optimum annealing parameters. Additionally, multivariable correlations that involve the Tellurium diffusion coefficient, annealing parameters, and CdZnTe properties will be analyzed. The experimental approach will involve systematic annealing experiments (in Cd vapor overpressure) on different sizes of CdZnTe crystals at varying temperature gradients ranging from 0 to 60°C/mm (used to migrate the Tellurium inclusion to one side of the crystal), and at annealing temperatures ranging

  5. Next Generation Semiconductor-Based Radiation Detectors Using Cadmium Magnesium Telluride

    SciTech Connect

    Trivedi, Sudhir B; Kutcher, Susan W; Palsoz, Witold; Berding, Martha; Burger, Arnold

    2014-11-17

    The primary objective of Phase I was to perform extensive studies on the purification, crystal growth and annealing procedures of CdMgTe to gain a clear understanding of the basic material properties to enable production of detector material with performance comparable to that of CdZnTe. Brimrose utilized prior experience in the growth and processing of II-VI crystals and produced high purity material and good quality single crystals of CdMgTe. Processing techniques for these crystals including annealing, mechanical and chemical polishing, surface passivation and electrode fabrication were developed. Techniques to characterize pertinent electronic characteristics were developed and gamma ray detectors were fabricated. Feasibility of the development of comprehensive defect modeling in this new class of material was demonstrated by our partner research institute SRI International, to compliment the experimental work. We successfully produced a CdMgTe detector that showed 662 keV gamma response with energy resolution of 3.4% (FWHM) at room temperature, without any additional signal correction. These results are comparable to existing CdZnTe (CZT) technology using the same detector size and testing conditions. We have successfully demonstrated detection of gamma-radiation from various isotopes/sources, using CdMgTe thus clearly proving the feasibility that CdMgTe is an excellent, low-cost alternative to CdZnTe.

  6. Characterisation of an electron collecting CdTe strip sensor using the MYTHEN readout chip

    NASA Astrophysics Data System (ADS)

    Elbracht-Leong, S.; Bergamaschi, A.; Greiffenberg, D.; Peake, D.; Rassool, R.; Schmitt, B.; Toyokawa, H.; Sobbott, B.

    2015-01-01

    MYTHEN is a single photon counting hybrid strip X-ray detector that has found application in x-ray powder diffraction (XRPD) experiments at synchrotrons worldwide. Originally designed to operate with hole collecting silicon sensors, MYTHEN is suited for detecting X-rays above 5 keV, however many PD beamlines have been designed for energies above 50 keV where silicon sensors have an efficiency of only few percent. In order to adapt MYTHEN to meet these energies the absorption efficiency of the sensor must be substantially increased. Cadmium-Telluride (CdTe) has an absorption efficiency approximately 30 times that of silicon at 50 keV, and is therefore a very promising replacement candidate for silicon. Furthermore, the large dynamic range of the pre-amplifier of MYTHEN and its double polarity capability has enabled the characterisation of an electron collecting Schottky type CdTe sensor. A CdTe MYTHEN system has undergone a series of characterisation experiments including stress test of bias and radiation induced polarizations. The performance of this system will be presented and discussed.

  7. Relationship between the cathodoluminescence emission and resistivity in In doped CdZnTe crystals

    SciTech Connect

    Rodriguez-Fernandez, J.; Carcelen, V.; Dieguez, E.; Hidalgo, P.; Piqueras, J.; Vijayan, N.; Sochinskii, N. V.; Perez, J. M.

    2009-08-15

    Cadmium zinc telluride, CdZnTe, bulk single crystals doped with 10{sup 19} at./cm{sup 3} of indium in the initial melt were grown by vertical Bridgman technique. The samples were investigated by energy dispersive spectroscopy, cathodoluminiscence (CL), and current-voltage behavior at room temperature. The results shows that Cd and Te vacancy concentration depend on the indium and zinc concentrations. CL measurements indicate a relationship between radiative centers associated to Cd and Te vacancies and resistivity values.

  8. Vanadium-Doped Cadmium Manganese Telluride (Cd1-X Mn (X) Te) Crystals as X- and Gamma-Ray Detectors

    SciTech Connect

    Hossain, A.; Cui, y; Bolotnikov, A; Camarda, G; Yang, G; Kochanowska, D; Witkowska-Baran, M; Mycielski, A; James, R

    2009-01-01

    CdMnTe offers several potential advantages over CdZnTe as a room- temperature gamma-ray detector, but many drawbacks in its growth process impede the production of large, defect-free single crystals with high electrical resistivity and high electron lifetimes. Here, we report our findings of the defects in several vanadium-doped as-grown as well as annealed Cd{sub 1-x} Mn{sub x} Te crystals, using etch pit techniques. We carefully selected single crystals from the raw wafer to fabricate and test as a gamma-ray detector. We describe the quality of the processed Cd{sub 1-x} Mn{sub x} Te surfaces, and compare them with similarly treated CdZnTe crystals. We discuss the characterization experiments aimed at clarifying the electrical properties of fabricated detectors, and evaluate their performance as gamma-ray spectrometers.

  9. Selective area epitaxy of CdTe

    NASA Astrophysics Data System (ADS)

    Luo, Y. Y.; Cavus, A.; Tamargo, M. C.

    1997-06-01

    We have performed selective area epitaxy (SAE) of CdTe layers grown by molecular beam epitaxy using a shadow mask technique. This technique was chosen over other SAE techniques due to its simplicity and its compatibility with multiple SAE patterning steps. Features as small as 50 microns × 50 microns were obtained with sharp, abrupt side walls and flat mesa tops. Separations between mesas as small as 20 microns were also obtained. Shadowing effects due to the finite thickness of the mask were reduced by placing the CdTe source in a near normal incidence position. Intimate contact between the mask and the substrate was essential in order to achieve good pattern definition.

  10. Schottky Barrier CdTe(Cl) Detectors for Planetary Missions

    NASA Astrophysics Data System (ADS)

    Eisen, Yosef; Floyd, Samuel

    2002-10-01

    Schottky barrier cadmium telluride (CdTe) radiation detectors of dimensions 2mm × 2mm × 1mm and segmented monolithic 3cm × 3 cm × 1mm are under study at GSFC for future NASA planetary instruments. These instruments will perform x-ray fluorescence spectrometry of the surface and monitor the solar x-ray flux spectrum, the excitation source for the characteristic x-rays emitted from the planetary body. The Near Earth Asteroid Rendezvous (NEAR) mission is the most recent example of such a remote sensing technique. Its x-ray fluorescence detectors were gas proportional counters with a back up Si PIN solar monitor. Analysis of NEAR data has shown the necessity to develop a solar x-ray detector with efficiency extending to 30keV. Proportional counters and Si diodes have low sensitivity above 9keV. Our 2mm × 2mm × 1mm CdTe operating at -30°C possesses an energy resolution of 250eV FWHM for 55Fe with unit efficiency to up to 30keV. This is an excellent candidate for a solar monitor. Another ramification of the NEAR data is a need to develop a large area detector system, 20-30 cm2, with cosmic ray charged particle rejection, for measuring the characteristic radiation. A 3cm × 3cm × 1mm Schottky CdTe segmented monolithic detector is under investigation for this purpose. A tiling of 2-3 such detectors will result in the desired area. The favorable characteristics of Schottky CdTe detectors, the system design complexities when using CdTe and its adaptation to future missions will be discussed.

  11. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-01-01

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate and electrolyzing the leachate to separate Cd from Te, wherein the Te is deposits onto a cathode while the Cd remains in solution.

  12. Electric field distributions in CdZnTe due to reduced temperature and x-ray irradiation

    SciTech Connect

    Sellin, P. J.; Prekas, G.; Franc, J.; Grill, R.

    2010-03-29

    Real-time Pockels imaging is performed on semi-insulating CdZnTe to measure the electric field profile in the material bulk. In steady-state room temperature conditions the measured electric field profile is uniform, consistent with a low space charge concentration. At temperatures <270 K a significant nonuniform electric field profile is observed, which we explain in terms of temperature-induced band bending at the metal-semiconductor interface, causing the formation of positive space charge in the bulk. Similar electric field distortion effects are observed when room temperature CdZnTe is irradiated by x-rays, causing a high rate of photoinduced charge injection.

  13. Evaluation of a CdTe semiconductor based compact gamma camera for sentinel lymph node imaging

    SciTech Connect

    Russo, Paolo; Curion, Assunta S.; Mettivier, Giovanni; Esposito, Michela; Aurilio, Michela; Caraco, Corradina; Aloj, Luigi; Lastoria, Secondo

    2011-03-15

    Purpose: The authors assembled a prototype compact gamma-ray imaging probe (MediPROBE) for sentinel lymph node (SLN) localization. This probe is based on a semiconductor pixel detector. Its basic performance was assessed in the laboratory and clinically in comparison with a conventional gamma camera. Methods: The room-temperature CdTe pixel detector (1 mm thick) has 256x256 square pixels arranged with a 55 {mu}m pitch (sensitive area 14.08x14.08 mm{sup 2}), coupled pixel-by-pixel via bump-bonding to the Medipix2 photon-counting readout CMOS integrated circuit. The imaging probe is equipped with a set of three interchangeable knife-edge pinhole collimators (0.94, 1.2, or 2.1 mm effective diameter at 140 keV) and its focal distance can be regulated in order to set a given field of view (FOV). A typical FOV of 70 mm at 50 mm skin-to-collimator distance corresponds to a minification factor 1:5. The detector is operated at a single low-energy threshold of about 20 keV. Results: For {sup 99m}Tc, at 50 mm distance, a background-subtracted sensitivity of 6.5x10{sup -3} cps/kBq and a system spatial resolution of 5.5 mm FWHM were obtained for the 0.94 mm pinhole; corresponding values for the 2.1 mm pinhole were 3.3x10{sup -2} cps/kBq and 12.6 mm. The dark count rate was 0.71 cps. Clinical images in three patients with melanoma indicate detection of the SLNs with acquisition times between 60 and 410 s with an injected activity of 26 MBq {sup 99m}Tc and prior localization with standard gamma camera lymphoscintigraphy. Conclusions: The laboratory performance of this imaging probe is limited by the pinhole collimator performance and the necessity of working in minification due to the limited detector size. However, in clinical operative conditions, the CdTe imaging probe was effective in detecting SLNs with adequate resolution and an acceptable sensitivity. Sensitivity is expected to improve with the future availability of a larger CdTe detector permitting operation at shorter

  14. Spent-fuel characterization with small CZT detectors

    NASA Astrophysics Data System (ADS)

    Berndt, R.; Mortreau, P.

    2006-08-01

    CdTe detectors may be utilised as miniature instruments for the measurement of gamma spectra in safeguards applications [R. Arlt, V. Gryshchuk, P. Sumah, Nucl. Instr. and Meth. A 428 (1999) 127]. This is applicable for measurements both to fresh fuel and irradiated nuclear fuel. The spectrum analysis, however, is more complicated than with Ge detectors. Some reasons are: the peaks are asymmetric, the peak/Compton ratio is low, peak parameters depend on the count rate and on the properties of individual detector crystals. We developed a spectrum-unfolding code for spectra obtained with CdTe detectors. The code makes use of a series of pattern spectra of the individual instrument. It is applied to fission-product spectra and allows the coarse characterisation of the spent fuel in safeguards inspections.

  15. Array of virtual Frisch-grid CZT detectors with common cathode readout and pulse-height correction

    SciTech Connect

    Bolotnikov, A.E.; Camarda, G.S.; Cui, Y.; Egarievwe, E.U.; Fochuk, P.M.; Fuerstnau, M.; Gul, R.; Hossain, A.; Jones, F.; Kim, K.; Kopach, O.V.; Taggart, R.; Yang, G.; Ye, Z.; Xu, L.; and James, R.B.

    2010-08-01

    We present our new results from testing 15-mm-long virtual Frisch-grid CdZnTe detectors with a common-cathode readout for correcting pulse-height distortions. The array employs parallelepiped-shaped CdZnTe (CZT) detectors of a large geometrical aspect ratio, with two planar contacts on the top and bottom surfaces (anode and cathode) and an additional shielding electrode on the crystal's sides to create the virtual Frisch-grid effect. We optimized the geometry of the device and improved its spectral response. We found that reducing to 5 mm the length of the shielding electrode placed next to the anode had no adverse effects on the device's performance. At the same time, this allowed corrections for electron loss by reading the cathode signals to obtain depth information.

  16. Effects of sub-bandgap illumination on electrical properties and detector performances of CdZnTe:In

    SciTech Connect

    Xu, Lingyan; Jie, Wanqi Zha, Gangqiang Feng, Tao; Wang, Ning; Xi, Shouzhi; Fu, Xu; Zhang, Wenlong; Xu, Yadong; Wang, Tao

    2014-06-09

    The effects of sub-bandgap illumination on electrical properties of CdZnTe:In crystals and spectroscopic performances of the fabricated detectors were discussed. The excitation process of charge carriers through thermal and optical transitions at the deep trap could be described by the modified Shockley-Read-Hall model. The ionization probability of the deep donor shows an increase under illumination, which should be responsible for the variation of electrical properties within CdZnTe bulk materials with infrared (IR) irradiation. By applying Ohm's law, diffusion model and interfacial layer-thermionic-diffusion theory, we obtain the decrease of bulk resistivity and the increase of space charge density in the illuminated crystals. Moreover, the illumination induced ionization will further contribute to improving carrier transport property and charge collection efficiency. Consequently, the application of IR irradiation in the standard working environment is of great significance to improve the spectroscopic characteristics of CdZnTe radiation detectors.

  17. Strong coupling and polariton lasing in Te based microcavities embedding (Cd,Zn)Te quantum wells

    SciTech Connect

    Rousset, J.-G. Piętka, B.; Król, M.; Mirek, R.; Lekenta, K.; Szczytko, J.; Borysiuk, J.; Suffczyński, J.; Kazimierczuk, T.; Goryca, M.; Smoleński, T.; Kossacki, P.; Nawrocki, M.; Pacuski, W.

    2015-11-16

    We report on properties of an optical microcavity based on (Cd,Zn,Mg)Te layers and embedding (Cd,Zn)Te quantum wells. The key point of the structure design is the lattice matching of the whole structure to MgTe, which eliminates the internal strain and allows one to embed an arbitrary number of unstrained quantum wells in the microcavity. We evidence the strong light-matter coupling regime already for the structure containing a single quantum well. Embedding four unstrained quantum wells results in further enhancement of the exciton-photon coupling and the polariton lasing in the strong coupling regime.

  18. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, R.E.; Long, M.O.; Drinkard, W.F. Jr.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base. 3 figs.

  19. Recycling of CdTe photovoltaic waste

    DOEpatents

    Goozner, Robert E.; Long, Mark O.; Drinkard, Jr., William F.

    1999-04-27

    A method for extracting and reclaiming metals from scrap CdTe photovoltaic cells and manufacturing waste by leaching the metals in dilute nitric acid, leaching the waste with a leaching solution comprising nitric acid and water, skimming any plastic material from the top of the leaching solution, separating the glass substrate from the liquid leachate, adding a calcium containing base to the leachate to precipitate Cd and Te, separating the precipitated Cd and Te from the leachate, and recovering the calcium-containing base.

  20. Simulation of Electric Field in Semi Insulating Au/CdTe/Au Detector under Flux

    SciTech Connect

    Franc, J.; James, R.; Grill, R.; Kubat, J.; Belas, E.; Hoschl, P.; Moravec, P.; Praus, P.

    2009-08-02

    We report our simulations on the profile of the electric field in semi insulating CdTe and CdZnTe with Au contacts under radiation flux. The type of the space charge and electric field distribution in the Au/CdTe/Au structure is at high fluxes result of a combined influence of charge formed due to band bending at the electrodes and from photo generated carriers, which are trapped at deep levels. Simultaneous solution of drift-diffusion and Poisson equations is used for the calculation. We show, that the space charge originating from trapped photo-carriers starts to dominate at fluxes 10{sup 15}-10{sup 16}cm{sup -2}s{sup -1}, when the influence of contacts starts to be negligible.

  1. HgCdTe mid-wavelength IR photovoltaic detectors fabricated using plasma induced junction technology

    NASA Astrophysics Data System (ADS)

    Dell, J. M.; Antoszewski, J.; Rais, M. H.; Musca, C.; White, J. K.; Nener, B. D.; Faraone, L.

    2000-06-01

    Preliminary characterization results are presented for mid-wave infrared (MWIR) mercury cadmium telluride n-on-p photodiodes fabricated using a plasma induced type conversion junction formation technology. The diodes have been fabricated on three different vacancy doped p-type epitaxial starting materials, grown by liquid phase epitaxy (LPE) on CdZnTe, LPE on sapphire, and P/p isotype heterojunction material grown by molecular beam epitaxy (MBE) on CdZnTe. All materials had CdTe mole fraction in the active region of the device of ˜0.3. The process uses a H2/CH4 plasma generated in a parallel plate reactive ion etching (RIE) system to type convert the p-type material to n-type. The process is different from previously reported type conversion techniques in that it does not require a high temperature anneal, does not expose the junction at the surface to atmosphere after formation, and requires significantly fewer process steps than other planar processes. Homojunction devices fabricated using this process exhibit R0A values >107 Ω·cm2 at 80 K. The R0A is diffusion limited for temperatures >˜135 K. Results for responsivity, bias dependence of dynamic resistance — junction area product and 1/f noise show that the resulting diodes are comparable to the best planar diodes reported in the literature.

  2. Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christian

    2014-03-12

    An impurity reaction-diffusion model is applied to Cu defects and related intrinsic defects in polycrystalline CdTe for a better understanding of Cu’s role in the cell level reliability of CdTe PV devices. The simulation yields transient Cu distributions in polycrystalline CdTe during solar cell processing and stressing. Preliminary results for Cu migration using available diffusivity and solubility data show that Cu accumulates near the back contact, a phenomena that is commonly observed in devices after back-contact processing or stress conditions.

  3. Process Development for High Voc CdTe Solar Cells

    SciTech Connect

    Ferekides, C. S.; Morel, D. L.

    2011-05-01

    This is a cumulative and final report for Phases I, II and III of this NREL funded project (subcontract # XXL-5-44205-10). The main research activities of this project focused on the open-circuit voltage of the CdTe thin film solar cells. Although, thin film CdTe continues to be one of the leading materials for large-scale cost-effective production of photovoltaics, the efficiency of the CdTe solar cells have been stagnant for the last few years. This report describes and summarizes the results for this 3-year research project.

  4. Iterative deconvolution of simultaneous 99mTc and 201Tl projection data measured on a CdZnTe based cardiac SPECT scanner

    PubMed Central

    Kacperski, Krzysztof; Erlandsson, Kjell; Ben-Haim, Simona; Hutton, Brian F.

    2011-01-01

    We present a method of correcting self-scatter and crosstalk effects in simultaneous technetium-99m/thallium-201 stress/rest myocardial perfusion SPECT scans. The method, which is in essence a hybrid between the TEW method and scatter modelling, is based on a model of spatial and spectral distribution of projection counts in several selected energy windows. The parameters of the model are determined from measurements of thin rod sources in air when no in-object scatter or attenuation effects are present. The model equations are solved using the iterative Maximum Likelihood Expectation Maximisation (ML-EM) algorithm in the projection space to find estimates of the primary photopeak counts of both radionuclides. The method has been developed particularly for a novel dedicated cardiac camera based on CdZnTe pixellated detectors, although it can also be adapted to a conventional scintillator camera. The method has been validated in anthropomorphic phantom experiments. Significant improvement in defect contrast has been observed with only moderate increase in image noise. The application of the method to patient data is ilustrated. PMID:21317483

  5. Characterization of the metal-semiconductor interface of gold contacts on CdZnTe formed by electroless deposition

    NASA Astrophysics Data System (ADS)

    Bell, Steven J.; Baker, Mark A.; Duarte, Diana D.; Schneider, Andreas; Seller, Paul; Sellin, Paul J.; Veale, Matthew C.; Wilson, Matthew D.

    2015-06-01

    Fully spectroscopic x/γ-ray imaging is now possible thanks to advances in the growth of wide-bandgap semiconductors. One of the most promising materials is cadmium zinc telluride (CdZnTe or CZT), which has been demonstrated in homeland security, medical imaging, astrophysics and industrial analysis applications. These applications have demanding energy and spatial resolution requirements that are not always met by the metal contacts deposited on the CdZnTe. To improve the contacts, the interface formed between metal and semiconductor during contact deposition must be better understood. Gold has a work function closely matching that of high resistivity CdZnTe and is a popular choice of contact metal. Gold contacts are often formed by electroless deposition however this forms a complex interface. The prior CdZnTe surface preparation, such as mechanical or chemo-mechanical polishing, and electroless deposition parameters, such as gold chloride solution temperature, play important roles in the formation of the interface and are the subject of the presented work. Techniques such as focused ion beam (FIB) cross section imaging, transmission electron microscopy (TEM), energy dispersive x-ray spectroscopy (EDS), x-ray photoelectron spectroscopy (XPS) and current  -  voltage (I-V) analysis have been used to characterize the interface. It has been found that the electroless reaction depends on the surface preparation and for chemo-mechanically polished (1 1 1) CdZnTe, it also depends on the A/B face identity. Where the deposition occurred at elevated temperature, the deposited contacts were found to produce a greater leakage current and suffered from increased subsurface voiding due to the formation of cadmium chloride.

  6. Accuracy of existing atomic potentials for the CdTe semiconductor compound.

    PubMed

    Ward, D K; Zhou, X W; Wong, B M; Doty, F P; Zimmerman, J A

    2011-06-28

    CdTe and CdTe-based Cd(1-x)Zn(x)Te (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided.

  7. Accuracy of existing atomic potentials for the CdTe semiconductor compound

    NASA Astrophysics Data System (ADS)

    Ward, D. K.; Zhou, X. W.; Wong, B. M.; Doty, F. P.; Zimmerman, J. A.

    2011-06-01

    CdTe and CdTe-based Cd1-xZnxTe (CZT) alloys are important semiconductor compounds that are used in a variety of technologies including solar cells, radiation detectors, and medical imaging devices. Performance of such systems, however, is limited due to the propensity of nano- and micro-scale defects that form during crystal growth and manufacturing processes. Molecular dynamics simulations offer an effective approach to study the formation and interaction of atomic scale defects in these crystals, and provide insight on how to minimize their concentrations. The success of such a modeling effort relies on the accuracy and transferability of the underlying interatomic potential used in simulations. Such a potential must not only predict a correct trend of structures and energies of a variety of elemental and compound lattices, defects, and surfaces but also capture correct melting behavior and should be capable of simulating crystalline growth during vapor deposition as these processes sample a variety of local configurations. In this paper, we perform a detailed evaluation of the performance of two literature potentials for CdTe, one having the Stillinger-Weber form and the other possessing the Tersoff form. We examine simulations of structures and the corresponding energies of a variety of elemental and compound lattices, defects, and surfaces compared to those obtained from ab initio calculations and experiments. We also perform melting temperature calculations and vapor deposition simulations. Our calculations show that the Stillinger-Weber parameterization produces the correct lowest energy structure. This potential, however, is not sufficiently transferrable for defect studies. Origins of the problems of these potentials are discussed and insights leading to the development of a more transferrable potential suitable for molecular dynamics simulations of defects in CdTe crystals are provided.

  8. Device Fabrication using Crystalline CdTe and CdTe Ternary Alloys Grown by MBE

    SciTech Connect

    Zaunbrecher, Katherine; Burst, James; Seyedmohammadi, Shahram; Malik, Roger; Li, Jian V.; Gessert, Timothy A.; Barnes, Teresa

    2015-06-14

    We fabricated epitaxial CdTe:In/CdTe:As homojunction and CdZnTe/CdTe and CdMgTe/CdTe heterojunction devices grown on bulk CdTe substrates in order to study the fundamental device physics of CdTe solar cells. Selection of emitter-layer alloys was based on passivation studies using double heterostructures as well as band alignment. Initial results show significant device integration challenges, including low dopant activation, high resistivity substrates and the development of low-resistance contacts. To date, the highest open-circuit voltage is 715 mV in a CdZnTe/CdTe heterojunction following anneal, while the highest fill factor of 52% was attained in an annealed CdTe homojunction. In general, all currentvoltage measurements show high series resistance, capacitancevoltages measurements show variable doping, and quantum efficiency measurements show low collection. Ongoing work includes overcoming the high resistance in these devices and addressing other possible device limitations such as non-optimum junction depth, interface recombination, and reduced bulk lifetime due to structural defects.

  9. Modeling Copper Diffusion in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystalline, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately

  10. Extracting Cu Diffusion Parameters in Polycrystalline CdTe

    SciTech Connect

    Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Guo, Da; Dragica, Vasileska; Ringhofer, Christian

    2014-06-13

    It is well known that Cu plays an important role in CdTe solar cell performance as a dopant. In this work, a finite-difference method is developed and used to simulate Cu diffusion in CdTe solar cells. In the simulations, which are done on a two-dimensional (2D) domain, the CdTe is assumed to be polycrystal-line, with the individual grains separated by grain boundaries. When used to fit experimental Cu concentration data, bulk and grain boundary diffusion coefficients and activation energies for CdTe can be extracted. In the past, diffusion coefficients have been typically obtained by fitting data to simple functional forms of limited validity. By doing full simulations, the simplifying assumptions used in those analytical models are avoided and diffusion parameters can thus be determined more accurately.

  11. CdTe Solar Cells: The Role of Copper

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christain

    2014-06-06

    In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

  12. Shuttle Mission STS-50: Orbital Processing of High-Quality CdTe Compound Semiconductors Experiment: Final Flight Sample Characterization Report

    NASA Technical Reports Server (NTRS)

    Larson, David J.; Casagrande, Luis G.; DiMarzio, Don; Alexander, J. Iwan D.; Carlson, Fred; Lee, Taipo; Dudley, Michael; Raghathamachar, Balaji

    1998-01-01

    The Orbital Processing of High-Quality Doped and Alloyed CdTe Compound Semiconductors program was initiated to investigate, quantitatively, the influences of gravitationally dependent phenomena on the growth and quality of bulk compound semiconductors. The objective was to improve crystal quality (both structural and compositional) and to better understand and control the variables within the crystal growth production process. The empirical effort entailed the development of a terrestrial (one-g) experiment baseline for quantitative comparison with microgravity (mu-g) results. This effort was supported by the development of high-fidelity process models of heat transfer, fluid flow and solute redistribution, and thermo-mechanical stress occurring in the furnace, safety cartridge, ampoule, and crystal throughout the melting, seeding, crystal growth, and post-solidification processing. In addition, the sensitivity of the orbital experiments was analyzed with respect to the residual microgravity (mu-g) environment, both steady state and g-jitter. CdZnTe crystals were grown in one-g and in mu-g. Crystals processed terrestrially were grown at the NASA Ground Control Experiments Laboratory (GCEL) and at Grumman Aerospace Corporation (now Northrop Grumman Corporation). Two mu-g crystals were grown in the Crystal Growth Furnace (CGF) during the First United States Microgravity Laboratory Mission (USML-1), STS-50, June 24 - July 9, 1992.

  13. Recrystallisation of electrophoretically deposited CdTe films

    NASA Astrophysics Data System (ADS)

    Pande, P. C.; Bocking, S.; Duke, S.; Miles, R. W.; Carter, M. J.; Latimer, I. D.; Hill, R.

    1996-02-01

    Films of CdTe have been produced by a novel low cost process based on electrophoretic deposition using polar organic solvents. The main advantage of this method is the high rate of deposition, greater than 20 μm/min. Details of the deposition process are given and the effects of post-deposition annealing of the samples have also been investigated using XRD, SEM and EDAX. Laser annealing resulted in melting of CdTe producing more compact and robust films.

  14. Strategies for recycling CdTe photovoltaic modules

    SciTech Connect

    Eberspacher, C.; Gay, C.F.; Moskowitz, P.D.

    1994-12-31

    Recycling end-of-life cadmium telluride (CdTe) photovoltaic (PV) modules may enhance the competitive advantage of CdTe PV in the marketplace, but the experiences of industries with comparable Environmental, Health and Safety (EH&S) challenges suggest that collection and recycling costs can impose significant economic burdens. Customer cooperation and pending changes to US Federal law may improve recycling economics.

  15. CdTe Photovoltaics for Sustainable Electricity Generation

    NASA Astrophysics Data System (ADS)

    Munshi, Amit; Sampath, Walajabad

    2016-09-01

    Thin film CdTe (cadmium telluride) is an important technology in the development of sustainable and affordable electricity generation. More than 10 GW of installations have been carried out using this technology around the globe. It has been demonstrated as a sustainable, green, renewable, affordable and abundant source of electricity. An advanced sublimation tool has been developed that allows highly controlled deposition of CdTe films onto commercial soda lime glass substrates. All deposition and treatment steps can be performed without breaking the vacuum within a single chamber in an inline process that can be conveniently scaled to a commercial process. In addition, an advanced cosublimation source has been developed to allow the deposition of ternary alloys such as Cd x Mg1- x Te to form an electron reflector layer which is expected to address the voltage deficits in current CdTe devices and to achieve very high efficiency. Extensive materials characterization, including but not limited to scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, high resolution transmission electron microscopy and electron back-scatter diffraction, has been performed to get a better understanding of the effects of processing conditions on CdTe thin film photovoltaics. This combined with computer modeling such as density function theory modeling gives a new insight into the mechanism of CdTe photovoltaic function. With all these efforts, CdTe photovoltaics has seen great progress in the last few years. Currently, it has been recorded as the cheapest source of electricity in the USA on a commercial scale, and further improvements are predicted to further reduce the cost while increasing its utilization. Here, we give an overview of the advantages of thin film CdTe photovoltaics as well as a brief review of the challenges that need to be addressed. Some fundamental studies of processing conditions for thin film CdTe are also presented

  16. High-quality CdTe films from nanoparticle precursors

    SciTech Connect

    Schulz, D.L.; Pehnt, M.; Urgiles, E.

    1996-05-01

    In this paper the authors demonstrate that nanoparticulate precursors coupled with spray deposition offers an attractive route into electronic materials with improved smoothness, density, and lower processing temperatures. Employing a metathesis approach, cadmium iodide was reacted with sodium telluride in methanol solvent, resulting in the formation of soluble NaI and insoluble CdTe nanoparticles. After appropriate chemical workup, methanol-capped CdTe colloids were isolated. CdTe thin film formation was achieved by spray depositing the nanoparticle colloids (25-75 {Angstrom} diameter) onto substrates at elevated temperatures (T = 280-440{degrees}C) with no further thermal treatment. These films were characterized by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). Cubic CdTe phase formation was observed by XRD, with a contaminant oxide phase also detected. XPS analysis showed that CdTe films produced by this one-step method contained no Na or C and substantial O. AFM gave CdTe grain sizes of {approx}0.1-0.3 {mu}m for film sprayed at 400{degrees}C. A layer-by-layer film growth mechanism proposed for the one-step spray deposition of nanoparticle precursors will be discussed.

  17. Imaging performance comparison between a LaBr3: Ce scintillator based and a CdTe semiconductor based photon counting compact gamma camera.

    PubMed

    Russo, P; Mettivier, G; Pani, R; Pellegrini, R; Cinti, M N; Bennati, P

    2009-04-01

    The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr3: Ce scintillator continuous crystal (49 x 49 x 5 mm3) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14 x 14 x 1 mm3) with 256 x 256 square pixels and a pitch of 55 microm, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 microm, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.

  18. A photon counting CdTe gamma- and X-ray camera

    NASA Astrophysics Data System (ADS)

    Spartiotis, Konstantinos; Leppänen, Anssi; Pantsar, Tuomas; Pyyhtiä, Jouni; Laukka, Pasi; Muukkonen, Kari; Männistö, Olli; Kinnari, Jussi; Schulman, Tom

    2005-09-01

    A photon counting CdTe imaging camera suitable for gamma- and X-ray detection has been developed and tested. The current full active imaging area of the gamma/X-ray camera covers 44×44 mm 2. The camera is built of eight individual detector hybrids each consisting of a pixelated CdTe detector with dimensions of 22×11 mm 2 and solder bump-bonded to a photon counting custom-designed application specific integrated circuit (ASIC). The ASICs are realized in a mixed signal, 0.35 μm 4 metal 2 poly CMOS process. The effective pixel size (image pixel pitch) is 0.5 mm. To enable higher count rate imaging and to achieve better position resolution in X-ray CT scanning each pixel is divided both on the CdTe detector and on the ASIC into two sub-pixels with dimensions 0.25×0.5 mm 2. Every pixel circuit has two preamps each connected to one sub-pixel and feeding signal to a separate comparator. The digital pulses of the two distinct comparators are recorded by one common 8-bit counter. The amplifier offsets can be adjusted individually with 3-bit accuracy to compensate for process mismatch. A similar 3-bit gain tuning common to the two amplifiers in one pixel circuit is also implemented. A globally tuneable threshold voltage generated externally with high accuracy is used for energy discrimination. The camera can be operated both in the real time imaging mode with a maximum speed of 100 frames/s and in the accumulation mode with user adjustable counting time. Experimental data collected from a fully operational eight hybrid gamma/X-ray camera is presented and compared to simulated data. The camera exhibits excellent sensitivity and a dynamic range of 1:14,000,000. A sharp line spread function indicates the spatial resolution to be limited only by the pixel size (0.5 mm). A single pixel energy resolution of FWHM 4.7 keV at 122 keV (3.9%) was determined from measured 57Co spectra. The peak width of the spectrum combined from all pixels was somewhat larger due to calibration

  19. Preparation and properties of evaporated CdTe films compared with single crystal CdTe. Progress report No. 1, October 1, 1980-January 31, 1981

    SciTech Connect

    Bube, R. H.

    1981-01-01

    This program is concerned with the investigation of the materials properties of CdTe thin films deposited by hot-wall vacuum evaporation and of CdTe single crystalline material, particularly those relevant to solar cell applications in which CdTe is the absorbing member. Progress is reported on: (a) an evaluation of CdTe homojunctions formed by HWVE of CdTe by Walter Huber at the laboratory of Dr. Adolfo Lopez-Otero at the Institut fuer Physik of the University of Linz, using single crystal p-type CdTe from Stanford as a substrate; (b) the design and construction of a HWVE apparatus at Stanford; and (c) properties of grain boundaries in large grain polycrystalline CdTe.

  20. CdTe Thin Film Solar Cells and Modules Tutorial; NREL (National Renewable Energy Laboratory)

    SciTech Connect

    Albin, David S.

    2015-06-13

    This is a tutorial presented at the 42nd IEEE Photovoltaics Specialists Conference to cover the introduction, background, and updates on CdTe cell and module technology, including CdTe cell and module structure and fabrication.

  1. Infrared detectors: State of art; Proceedings of the Meeting, San Diego, CA, July 23, 24, 1992

    NASA Astrophysics Data System (ADS)

    Makky, Wagih H.

    1992-12-01

    The present conference discusses innovative IR detection devices and technologies, HgCdTe-based IR detectors, and quantum-well (QW) devices. Attention is given to uncooled thermal imaging, intersubband transitions and IR hot-electron transistors, the consideration of a novel two-color IR detector on the basis of the 'two-peak' effect, recent developments in MOCVD of Hg(1-x)Cd(x)Te photodiode arrays, and the growth of HgCdTe by MBE on CdZnTe substrates. Also discussed are Si-based QW intersubband detectors, increased responsivity and detectivity in asymmetric QW IR detectors, IR internal emission detectors, an InSb monolithic focal-plane cell, and surface plasmons on PtSi for visible and Si Schottky-barrier-enhanced detection. (No individual items are abstracted in this volume)

  2. Large format MBE HgCdTe on silicon detector development for astronomy

    NASA Astrophysics Data System (ADS)

    Hanold, Brandon J.; Figer, Donald F.; Lee, Joong; Kolb, Kimberly; Marcuson, Iain; Corrales, Elizabeth; Getty, Jonathan; Mears, Lynn

    2015-08-01

    The Center for Detectors at Rochester Institute of Technology and Raytheon Vision Systems (RVS) are leveraging RVS capabilities to produce large format, short-wave infrared HgCdTe focal plane arrays on silicon (Si) substrate wafers. Molecular beam epitaxial (MBE) grown HgCdTe on Si can reduce detector fabrication costs dramatically, while keeping performance competitive with HgCdTe grown on CdZnTe. Reduction in detector costs will alleviate a dominant expense for observational astrophysics telescopes. This paper presents the characterization of 2.5μm cutoff MBE HgCdTe/Si detectors including pre- and post-thinning performance. Detector characteristics presented include dark current, read noise, spectral response, persistence, linearity, crosstalk probability, and analysis of material defects.

  3. Thin film cadmium telluride charged particle sensors for large area neutron detectors

    SciTech Connect

    Murphy, J. W.; Smith, L.; Calkins, J.; Mejia, I.; Cantley, K. D.; Chapman, R. A.; Quevedo-Lopez, M.; Gnade, B.; Kunnen, G. R.; Allee, D. R.; Sastré-Hernández, J.; Contreras-Puente, G.; Mendoza-Pérez, R.

    2014-09-15

    Thin film semiconductor neutron detectors are an attractive candidate to replace {sup 3}He neutron detectors, due to the possibility of low cost manufacturing and the potential for large areas. Polycrystalline CdTe is found to be an excellent material for thin film charged particle detectors—an integral component of a thin film neutron detector. The devices presented here are characterized in terms of their response to alpha and gamma radiation. Individual alpha particles are detected with an intrinsic efficiency of >80%, while the devices are largely insensitive to gamma rays, which is desirable so that the detector does not give false positive counts from gamma rays. The capacitance-voltage behavior of the devices is studied and correlated to the response due to alpha radiation. When coupled with a boron-based neutron converting material, the CdTe detectors are capable of detecting thermal neutrons.

  4. High-temporal-resolution CdTe nuclear stethoscope for cardiac γ-ventriculography: preclinical evaluation

    NASA Astrophysics Data System (ADS)

    Eclancher, Bernard; Arntz, Y.; Chambron, Jacques; Prat, Vincent; Perret, C.; Karman, Miklos; Pszota, Agnes; Nemeth, Laszlo

    1999-10-01

    A hand-size probe including 64 elementary 5 X 5 X 2 mm CdTe detectors has been optimized to detect the (gamma) tracer 99Tc in the heart left ventricle. The system, has been developed, not for imaging, allowing acquisitions at 33 Hz to describe the labeled blood volume variations. The (gamma) -counts variations were found accurately proportional to the known volume variations of an artificial ventricle paced at variable rate and systolic volume. Softwares for on line data monitoring and for post-processing have been developed for beat to beat assessment of cardiac performance at rest and during physical exercise. The evaluation of this probe has been performed on 5 subjects in the Nucl Dep of Balatonfured Cardiology Hospital. It appears that the probe needs to be better shielded to work properly in the hot environment of the ventricle, but can provide reliable ventriculography, even under heavy exercise load, although the ventricle volume itself is unknown.

  5. The composition effect on the thermal and optical properties across CdZnTe crystals

    NASA Astrophysics Data System (ADS)

    Strzałkowski, K.

    2016-11-01

    Cd1‑x Zn x Te mixed crystals investigated in this work were grown from the melt using the vertical Bridgman–Stockbarger method in the whole range of composition 0  <  x  <  1 that is from one binary crystal (CdTe) to another (ZnTe). The real composition of grown crystals was measured with the SEM/EDS method along the growth axis. The segregation coefficient of Zn in a CdTe matrix has been evaluated as being close to unity. The energy gap as a function of the composition was determined from transmission spectroscopy. Thanks to that, the bowing parameter of this ternary alloy was found to be 0.458. In this work the systematical study of thermal properties of Cd1‑x Zn x Te alloys from one binary crystal (CdTe) to another (ZnTe) grown by the vertical Bridgman technique were undertaken for the first time. The thermal diffusivity and effusivity of the investigated crystals were derived from the experimental data and allowed the thermal conductivity to be calculated. Diagrams of the thermal conductivity versus composition were analyzed applying the model for mixed semiconducting crystals given by Sadao Adachi. Thanks to that, the contribution of the thermal resistivity arising from the lattice disorder to the total resistivity of the crystal has been determined.

  6. Reduced blinking behavior of single 2-mercapto ethanol capped CdTe quantum dots

    NASA Astrophysics Data System (ADS)

    Mandal, Abhijit; Tamai, Naoto

    2013-11-01

    Water soluble small size CdTe QDs were synthesized by using 2-mercapto ethanol (2ME) as stabilizer. The optimum size of QDs was obtained after certain time of reflux. Synthesized 2ME capped CdTe QDs show large Stokes shifted photoluminescence. At the single particle detection level, 2ME capped CdTe QDs showed reduced blinking behavior compared to that of TGA capped CdTe QDs. These results indicate that the thiol moiety of 2ME, which is a strong electron donor, saturated the surface traps with electrons, preventing the traps from accepting the Auger ionized electrons from the core of CdTe QD.

  7. Advances in CdTe R&D at NREL

    SciTech Connect

    Wu, X.; Zhou, J.; Keane, J. C.; Dhere, R. G.; Albin, D. S.; Gessert, T. A.; DeHart, C.; Duda, A.; Ward, J. J.; Yan, Y.; Teeter, G.; Levi, D. H.; Asher, S.; Perkins, C.; Moutinho, H. R.; To, B.

    2005-11-01

    This paper summarizes the following R&D accomplishments at National Renewable Energy Laboratory (NREL): (1) Developed several novel materials and world-record high-efficiency CdTe solar cell, (2) Developed "one heat-up step" manufacturing processes, and (3) Demonstrated 13.9% transparent CdTe cell and 15.3% CdTe/CIS polycrystalline tandem solar cell. Cadmium telluride has been well recognized as a promising photovoltaic material for thin-film solar cells because of its near-optimum bandgap of ~1.5 eV and its high absorption coefficient. Impressive results have been achieved in the past few years for polycrystalline CdTe thin-film solar cells at NREL. In this paper, we summarize some recent R&D activities at NREL.

  8. Resetting the Defect Chemistry in CdTe

    SciTech Connect

    Metzger, Wyatt K.; Burst, James; Albin, David; Colegrove, Eric; Moseley, John; Duenow, Joel; Farrell, Stuart; Moutinho, Helio; Reese, Matt; Johnston, Steve; Barnes, Teresa; Perkins, Craig; Guthrey, Harvey; Al-Jassim, Mowafak

    2015-06-14

    CdTe cell efficiencies have increased from 17% to 21% in the past three years and now rival polycrystalline Si [1]. Research is now targeting 25% to displace Si, attain costs less than 40 cents/W, and reach grid parity. Recent efficiency gains have come largely from greater photocurrent. There is still headroom to lower costs and improve performance by increasing open-circuit voltage (Voc) and fill factor. Record-efficiency CdTe cells have been limited to Voc <; 880 mV, whereas GaAs can attain Voc of 1.10 V with a slightly smaller bandgap [2,3]. To overcome this barrier, we seek to understand and increase lifetime and carrier concentration in CdTe. In polycrystalline structures, lifetime can be limited by interface and grain-boundary recombination, and attaining high carrier concentration is complicated by morphology.

  9. Effect of thickness on physical properties of electron beam vacuum evaporated CdZnTe thin films for tandem solar cells

    NASA Astrophysics Data System (ADS)

    Chander, Subhash; Dhaka, M. S.

    2016-10-01

    The thickness and physical properties of electron beam vacuum evaporated CdZnTe thin films have been optimized in the present work. The films of thickness 300 nm and 400 nm were deposited on ITO coated glass substrates and subjected to different characterization tools like X-ray diffraction (XRD), UV-Vis spectrophotometer, source meter and scanning electron microscopy (SEM) to investigate the structural, optical, electrical and surface morphological properties respectively. The XRD results show that the as-deposited CdZnTe thin films have zinc blende cubic structure and polycrystalline in nature with preferred orientation (111). Different structural parameters are also evaluated and discussed. The optical study reveals that the optical transition is found to be direct and energy band gap is decreased for higher thickness. The transmittance is found to increase with thickness and red shift observed which is suitable for CdZnTe films as an absorber layer in tandem solar cells. The current-voltage characteristics of deposited films show linear behavior in both forward and reverse directions as well as the conductivity is increased for higher film thickness. The SEM studies show that the as-deposited CdZnTe thin films are found to be homogeneous, uniform, small circle-shaped grains and free from crystal defects. The experimental results confirm that the film thickness plays an important role to optimize the physical properties of CdZnTe thin films for tandem solar cell applications as an absorber layer.

  10. Atomic Structure of Twin Boundaries in CdTe

    SciTech Connect

    Yan, Y.; Jones, K. M.; Al-Jassim, M. M.

    2003-05-01

    Using the combination of high-resolution transmission electron microscopy, first-principles density-functional total energy calculations, and image simulations, we determined the atomic structure of lamellar twin and double-positioning twin boundaries in CdTe. We find that the structure of lamellar twin boundaries has no dangling bonds or wrong bonds; thus, it results in negligible effects on the electronic properties. The structure of double-positioning twin boundaries, however, contain both Cd and Te dangling bonds, and therefore produce energy states in the bandgap that are detrimental to the electronic properties of CdTe.

  11. THE EFFECT OF VARIOUS DETECTOR GEOMETRIES ON THE PERFORMANCE OF CZT USING ONE CRYSTAL

    SciTech Connect

    Washington, A.; Duff, M.; Teague, L.

    2011-06-21

    CdZnTe (CZT) continues to be a major thrust interest mainly due to its potential application as a room temperature radiation detector. The performance of CZT detectors is directly related to the charge collection ability which can be affected by the configuration of the electrical contact. The charge collection efficiency is determined in part by the specific geometry of the anode contact which serves as the readout electrode. In this report, contact geometries including single pixel, planar, coplanar, and dual anode will be systematically explored by comparing the performance efficiencies of the detector using both low and high energy gamma rays. To help eliminate the effect of crystal quality variations, the contact geometries were fabricated on the same crystal detector with minimal polishing between contact placements.

  12. Ion-beam-induced damage formation in CdTe

    SciTech Connect

    Rischau, C. W.; Schnohr, C. S.; Wendler, E.; Wesch, W.

    2011-06-01

    Damage formation in <111>- and <112>-oriented CdTe single crystals irradiated at room temperature and 15 K with 270 keV Ar or 730 keV Sb ions was investigated in situ using Rutherford backscattering spectroscopy (RBS) in channeling configuration. Defect profiles were calculated from the RBS spectra using the computer code DICADA and additional energy-dependent RBS measurements were performed to identify the type of defects. At both temperatures no formation of a buried amorphous layer was detected even after prolonged irradiation with several 10{sup 16} ions/cm{sup 2}. The fact that CdTe is not rendered amorphous even at 15 K suggests that the high resistance to amorphization is caused by the high ionicity of CdTe rather than thermal effects. The calculated defect profiles show the formation of a broad defect distribution that extends much deeper into the crystal than the projected range of the implanted ions at both temperatures. The post-range defects in CdTe thus do not seem to be of thermal origin either, but are instead believed to result from migration driven by the electronic energy loss.

  13. Radiative and interfacial recombination in CdTe heterostructures

    SciTech Connect

    Swartz, C. H. Edirisooriya, M.; LeBlanc, E. G.; Noriega, O. C.; Jayathilaka, P. A. R. D.; Ogedengbe, O. S.; Hancock, B. L.; Holtz, M.; Myers, T. H.; Zaunbrecher, K. N.

    2014-12-01

    Double heterostructures (DH) were produced consisting of a CdTe film between two wide band gap barriers of CdMgTe alloy. A combined method was developed to quantify radiative and non-radiative recombination rates by examining the dependence of photoluminescence (PL) on both excitation intensity and time. The measured PL characteristics, and the interface state density extracted by modeling, indicate that the radiative efficiency of CdMgTe/CdTe DHs is comparable to that of AlGaAs/GaAs DHs, with interface state densities in the low 10{sup 10 }cm{sup −2} and carrier lifetimes as long as 240 ns. The radiative recombination coefficient of CdTe is found to be near 10{sup −10} cm{sup 3}s{sup −1}. CdTe film growth on bulk CdTe substrates resulted in a homoepitaxial interface layer with a high non-radiative recombination rate.

  14. Growth of CdZnTe Crystals the Bridgman Technique with Controlled Overpressures of Cd

    NASA Technical Reports Server (NTRS)

    Su, Ching-Hu; Lehoczky, S. L.

    2008-01-01

    Cd(1-x)Zn(x)Te crystals with x = 0.15 and 0.20, were grown in this study by closed-ampoule directional solidification (Bridgman) technique with a controlled Cd overpressure. The growth ampoule was made of quartz with inner diameter from 20 to 40 mm and a tapered length of 2.5 cm at the growth tip. Both unseeded and seeded growths were performed with total material charges up to 400 g. After the loading of starting CdZnTe material, a typical amount of 2 g of Cd was also loaded inside a Cd reservoir basket, which was attached beneath the seal-off cup. The ampoule was sealed off under a vacuum below lxl0(exp -5) Torr. The sealed ampoule was placed inside a 4-zone Bridgman furnace - a Cd reservoir zone with a heat-pipe furnace liner on the top, followed by a hot zone, a booster heating zone and a cold zone at the bottom. The Cd zone was typically 300 to 400 C below the hot zone setting. High resistivity material has been obtained without any intentional dopants but has been reproducibly obtained with In doping. The crystalline and the electrical properties of the crystals will be reported.

  15. Development of CdZnTe energy selective arrays for industrial and medical radiation imaging

    NASA Astrophysics Data System (ADS)

    Polichar, Raulf; Schirato, Richard; Reed, John

    1994-12-01

    Recent advances in the production of CdZnTe using the high pressure Bridgman growth process now make it possible to design and fabricate complex X-ray sensor arrays on large monolithic substrates. These solid state ionization devices have the advantages of improved spatial and energy resolution, and produce significantly higher signals than competitive scintillator-photodiode systems. We have fabricated a number of linear and areal monolithic arrays in our laboratory using vacuum deposited contacts on such material with good success. These arrays operate in a pulse counting mode using hybrid and surface mount circuitry mounted in close proximity to the arrays. Linear devices with pitches of less than 0.8 mm and with 32 elements per substrate have been used for very wide dynamic range radioscopy with excellent results. Images are presented which demonstrate dynamic range in excess of 500:1 and Nyquist limited resolution at diagnostic X-ray energies for a wide variety of samples. Preliminary results demonstrate that the arrays can be used for energy selective radioscopy permitting the identification of differing materials within the image by approximate atomic number. Systems using areal arrays also have been evaluated as radiation cameras and demonstrate good spatial and energy resolution. Examples of data taken with a pin-hole collimator show the ability to distinguish source distributions by energy as well as location and intensity. Ongoing work in the improvement of spatial and energy resolution and the fabrication of larger arrays is discussed.

  16. Radiation detectors: needs and prospects

    SciTech Connect

    Armantrout, G.A.

    1981-01-01

    Important applications for x- and ..gamma..-ray spectroscopy are found in prospecting, materials characterization, environmental monitoring, the life sciences, and nuclear physics. The specific requirements vary for each application with varying degrees of emphasis on either spectrometer resolution, detection efficiency, or both. Since no one spectrometer is ideally suited to this wide range of needs, compromises are usually required. Gas and scintillation spectrometers have reached a level of maturity, and recent interest has concentrated on semiconductor spectrometers. Germanium detectors are showing continuing refinement and are the spectrometers of choice for high resolution applications. The new high-Z semiconductors, such as CdTe and HgI/sub 2/, have shown steady improvement but are limited in both resolution and size and will likely be used only in applications which require their unique properties.

  17. Electrostatic assembles and optical properties of Au CdTe QDs and Ag/Au CdTe QDs

    NASA Astrophysics Data System (ADS)

    Yang, Dongzhi; Wang, Wenxing; Chen, Qifan; Huang, Yuping; Xu, Shukun

    2008-09-01

    Au-CdTe and Ag/Au-CdTe assembles were firstly investigated through the static interaction between positively charged cysteamine-stabilized CdTe quantum dots (QDs) and negatively charged Au or core/shell Ag/Au nano-particles (NCs). The CdTe QDs synthesized in aqueous solution were capped with cysteamine which endowed them positive charges on the surface. Both Au and Ag/Au NCs were prepared through reducing precursors with gallic acid obtained from the hydrolysis of natural plant poly-phenols and favored negative charges on the surface of NCs. The fluorescence spectra of CdTe QDs exhibited strong quenching with the increase of added Au or Ag/Au NCs. Railey resonance scattering spectra of Au or Ag/Au NCs increased firstly and decreased latter with the concentration of CdTe QDs, accompanied with the solution color changing from red to purple and colorless at last. Experimental results on the effects of gallic acid, chloroauric acid tetrahydrate and other reagents demonstrated the static interaction occurred between QDs and NCs. This finding reveals the possibilities to design and control optical process and electromagnetic coupling in hybrid structures.

  18. Modification of solid state CdZnTe (CZT) radiation detectors with high sensitivity or high resolution operation

    SciTech Connect

    Washington, II, Aaron L; Duff, Martine C; Teague, Lucile C; Burger, Arnold; Groza, Michael

    2014-11-11

    An apparatus and process is provided to illustrate the manipulation of the internal electric field of CZT using multiple wavelength light illumination on the crystal surface at RT. The control of the internal electric field is shown through the polarization in the IR transmission image under illumination as a result of the Pockels effect.

  19. Direct Measurement of Mammographic X-Ray Spectra with a Digital CdTe Detection System

    PubMed Central

    Abbene, Leonardo; Gerardi, Gaetano; Principato, Fabio; Sordo, Stefano Del; Raso, Giuseppe

    2012-01-01

    In this work we present a detection system, based on a CdTe detector and an innovative digital pulse processing (DPP) system, for high-rate X-ray spectroscopy in mammography (1–30 keV). The DPP system performs a height and shape analysis of the detector pulses, sampled and digitized by a 14-bit, 100 MHz ADC. We show the results of the characterization of the detection system both at low and high photon counting rates by using monoenergetic X-ray sources and a nonclinical X-ray tube. The detection system exhibits excellent performance up to 830 kcps with an energy resolution of 4.5% FWHM at 22.1 keV. Direct measurements of clinical molybdenum X-ray spectra were carried out by using a pinhole collimator and a custom alignment device. A comparison with the attenuation curves and the half value layer values, obtained from the measured and simulated spectra, from an ionization chamber and from a solid state dosimeter, also shows the accuracy of the measurements. These results make the proposed detection system a very attractive tool for both laboratory research, calibration of dosimeters and advanced quality controls in mammography. PMID:22969406

  20. Characterization of CdTe Films Deposited at Various Bath Temperatures and Concentrations Using Electrophoretic Deposition

    PubMed Central

    Daud, Mohd Norizam Md; Zakaria, Azmi; Jafari, Atefeh; Ghazali, Mohd Sabri Mohd; Abdullah, Wan Rafizah Wan; Zainal, Zulkarnain

    2012-01-01

    CdTe film was deposited using the electrophoretic deposition technique onto an ITO glass at various bath temperatures. Four batch film compositions were used by mixing 1 to 4 wt% concentration of CdTe powder with 10 mL of a solution of methanol and toluene. X-ray Diffraction analysis showed that the films exhibited polycrystalline nature of zinc-blende structure with the (111) orientation as the most prominent peak. From the Atomic Force Microscopy, the thickness and surface roughness of the CdTe film increased with the increase of CdTe concentration. The optical energy band gap of film decreased with the increase of CdTe concentration, and with the increase of isothermal bath temperature. The film thickness increased with respect to the increase of CdTe concentration and bath temperature, and following, the numerical expression for the film thickness with respect to these two variables has been established. PMID:22754325

  1. First-principles study of roles of Cu and Cl in polycrystalline CdTe

    DOE PAGES

    Yang, Ji -Hui; Yin, Wan -Jian; Park, Ji -Sang; Metzger, Wyatt; Wei, Su -Huai

    2016-01-25

    In this study, Cu and Cl treatments are important processes to achieve high efficiency polycrystalline cadmium telluride (CdTe) solar cells, thus it will be beneficial to understand the roles they play in both bulk CdTe and CdTe grain boundaries (GBs). Using first-principles calculations, we systematically study Cu and Cl-related defects in bulk CdTe. We find that Cl has only a limited effect on improving p-type doping and too much Cl can induce deep traps in bulk CdTe, whereas Cu can enhance ptype doping of bulk CdTe. In the presence of GBs, we find that, in general, Cl and Cu willmore » prefer to stay at GBs, especially for those with Te-Te wrong bonds, in agreement with experimental observations.« less

  2. Study of the initial stages of growth of CdTe on (001)GaAs

    NASA Astrophysics Data System (ADS)

    Mar, H. A.; Salansky, N.; Chee, K. T.

    1984-05-01

    The initial stages of growth of CdTe on (001) GaAs have been studied using Auger electron spectroscopy and reflection high-energy electron techniques. At the growth temperature of 225 °C tellurium atoms are observed to be adsorbed to a thickness of one to two monolayers on a thermally cleaned GaAs substrate. However, cadmium atoms are adsorbed only when tellurium atoms are present. An analysis of the Auger electron spectra and the reflection high-energy electron diffraction patterns taken at intervals during the initial growth of CdTe films from a CdTe compound source indicates that growth takes place first by the deposition of one to two monolayers of tellurium. This is followed by the nucleation and growth of CdTe crystallites which increase in size and coalesce to form a single crystal of CdTe with a (111) CdTe ∥ (001) GaAs orientation.

  3. Charge Loss and Charge Sharing Measurements for Two Different Pixelated Cadmium-Zinc-Telluride Detectors

    NASA Technical Reports Server (NTRS)

    Gaskin, Jessica; Sharma, Dharma; Ramsey, Brian; Seller, Paul

    2003-01-01

    As part of ongoing research at Marshall Space Flight Center, Cadmium-Zinc- Telluride (CdZnTe) pixilated detectors are being developed for use at the focal plane of the High Energy Replicated Optics (HERO) telescope. HERO requires a 64x64 pixel array with a spatial resolution of around 200 microns (with a 6m focal length) and high energy resolution (< 2% at 60keV). We are currently testing smaller arrays as a necessary first step towards this goal. In this presentation, we compare charge sharing and charge loss measurements between two devices that differ both electronically and geometrically. The first device consists of a 1-mm-thick piece of CdZnTe that is sputtered with a 4x4 array of pixels with pixel pitch of 750 microns (inter-pixel gap is 100 microns). The signal is read out using discrete ultra-low-noise preamplifiers, one for each of the 16 pixels. The second detector consists of a 2-mm-thick piece of CdZnTe that is sputtered with a 16x16 array of pixels with a pixel pitch of 300 microns (inter-pixel gap is 50 microns). Instead of using discrete preamplifiers, the crystal is bonded to an ASIC that provides all of the front-end electronics to each of the 256 pixels. what degree the bias voltage (i.e. the electric field) and hence the drift and diffusion coefficients affect our measurements. Further, we compare the measured results with simulated results and discuss to

  4. Electrical properties of Au/CdZnTe/Au detectors grown by the boron oxide encapsulated Vertical Bridgman technique

    NASA Astrophysics Data System (ADS)

    Turturici, A. A.; Abbene, L.; Gerardi, G.; Benassi, G.; Bettelli, M.; Calestani, D.; Zambelli, N.; Raso, G.; Zappettini, A.; Principato, F.

    2016-09-01

    In this work we report on the results of electrical characterization of new CdZnTe detectors grown by the Boron oxide encapsulated Vertical Bridgman technique (B-VB), currently produced at IMEM-CNR (Parma, Italy). The detectors, with gold electroless contacts, have different thicknesses (1 and 2.5 mm) and the same electrode layout, characterized by a central anode surrounded by a guard-ring electrode. Investigations on the charge transport mechanisms and the electrical contact properties, through the modeling of the measured current-voltage (I-V) curves, were performed. Generally, the detectors are characterized by low leakage currents at high bias voltages even at room temperature: 34 nA/cm2 (T=25 °C) at 10,000 V/cm, making them very attractive for high flux X-ray measurements, where high bias voltage operation is required. The Au/CdZnTe barrier heights of the devices were estimated by using the interfacial layer-thermionic-diffusion (ITD) model in the reverse bias voltage range. Comparisons with CdZnTe detectors, grown by Traveling Heater Method (THM) and characterized by the same electrode layout, deposition technique and resistivity, were also performed.

  5. SWIR detectors for night vision at AIM

    NASA Astrophysics Data System (ADS)

    Figgemeier, H.; Benecke, M.; Hofmann, K.; Oelmaier, R.; Sieck, A.; Wendler, J.; Ziegler, J.

    2014-06-01

    Detectors for the short-wave infrared (SWIR) spectral range are particularly suitable for observation under hazy weather conditions as well as under twilight or moon light conditions. In addition, SWIR detectors allow using the airglow for observation under moonless sky. SWIR detectors are commonly based on InGaAs or HgCdTe (MCT) and demand extremely low dark currents to ensure a high signal-to-noise ratio under low background light conditions. AIM has developed a read-out integrated circuit (ROIC) with 640×512 pixels and a 15 μm pixel pitch for low light level applications. The ROIC supports analog or digital correlated double sampling (CDS) for the reduction of reset-noise (also known as kTC-noise). Along with CDS, a rolling shutter (RS) mode has been implemented. The input stage of the ROIC is based on a capacitive transimpedance amplifier (CTIA) with two selectable gain settings. The dark current of our SWIR MCT detectors has recently been significantly reduced to allow for high operating temperatures. In contrast to InGaAs, the MCT material offers the unique possibility to adjust the cut-off wavelength according to the application while maintaining the matching of the lattice constant to the one of the CdZnTe substrate. The key electro-optical performance parameters of lately developed MCT based SWIR Focal Plane Arrays (FPA) with a 1.75 μm cut-off wavelength will be presented. In addition, AIMs SWIR detectors covering the spectral range from 0.9 μm to 2.5 μm and available in formats of 384×288 pixels - 24 μm pitch and 1024×256 pixels - 24×32 μm2, will be introduced.

  6. Choice of Substrate Material for Epitaxial CdTe Solar Cells

    SciTech Connect

    Song, Tao; Kanevce, Ana; Sites, James R.

    2015-06-14

    Epitaxial CdTe with high quality, low defect density, and high carrier concentration should in principle yield high-efficiency photovoltaic devices. However, insufficient effort has been given to explore the choice of substrate for high-efficiency epitaxial CdTe solar cells. In this paper, we use numerical simulations to investigate three crystalline substrates: silicon (Si), InSb, and CdTe each substrate material are generally discussed.

  7. Imaging performance comparison between a LaBr{sub 3}:Ce scintillator based and a CdTe semiconductor based photon counting compact gamma camera

    SciTech Connect

    Russo, P.; Mettivier, G.; Pani, R.; Pellegrini, R.; Cinti, M. N.; Bennati, P.

    2009-04-15

    The authors report on the performance of two small field of view, compact gamma cameras working in single photon counting in planar imaging tests at 122 and 140 keV. The first camera is based on a LaBr{sub 3}:Ce scintillator continuous crystal (49x49x5 mm{sup 3}) assembled with a flat panel multianode photomultiplier tube with parallel readout. The second one belongs to the class of semiconductor hybrid pixel detectors, specifically, a CdTe pixel detector (14x14x1 mm{sup 3}) with 256x256 square pixels and a pitch of 55 {mu}m, read out by a CMOS single photon counting integrated circuit of the Medipix2 series. The scintillation camera was operated with selectable energy window while the CdTe camera was operated with a single low-energy detection threshold of about 20 keV, i.e., without energy discrimination. The detectors were coupled to pinhole or parallel-hole high-resolution collimators. The evaluation of their overall performance in basic imaging tasks is presented through measurements of their detection efficiency, intrinsic spatial resolution, noise, image SNR, and contrast recovery. The scintillation and CdTe cameras showed, respectively, detection efficiencies at 122 keV of 83% and 45%, intrinsic spatial resolutions of 0.9 mm and 75 {mu}m, and total background noises of 40.5 and 1.6 cps. Imaging tests with high-resolution parallel-hole and pinhole collimators are also reported.

  8. Development of EXITE3, Imaging Detectors and a Long Duration Balloon Gondola

    NASA Technical Reports Server (NTRS)

    2003-01-01

    In this Report we summarize the work conducted for the EXITE program under grant NAG5-5103. This grant supported the ongoing EXITE program at Harvard for the development of imaging hard x-ray detectors and telescopes over the 3 year period 1997-2000 with a one year extension to 2001 to transition to the next SR&T grant in this program. Work was conducted in three major parts: analysis of the EXITE2 balloon flight data (from our May 1997 flight); development of pixellated imaging Cd-Zn-Te detector arrays and readout systems for the proposed EXITE3 detector and telescope; and development of systems for a Long Duration Balloon (LDB) gondola. Progress on all three major aspects of this research is summarized for each of the years of this grant.

  9. Flight Performance and Laboratory Tests of CZT detectors for Hard X-ray Focal Planes

    NASA Astrophysics Data System (ADS)

    Baumgartner, Wayne; Harrison, F.; Chen, H.; Cook, W.; Craig, B.; Kruse-Madsen, K.; Boggs, S.; Wunderer, C.; Zoglauer, A.

    2006-09-01

    The next generation of hard X-ray instruments will employ focusing telescopes, which can achieve orders of magnitude improvement in sensitivity compared to current instruments on modest sized platforms. Solid state Cadmium Zinc Telluride pixel detectors have recently been developed and implemented as focal plane detectors for these new telescopes, since they can achieve good imaging and spectral performance from X-ray energies of a few keV to greater than 100 keV. We have developed a high-performance Cd(Zn)Te pixel detector for use with the High Energy Focusing Telescope balloon experiment, and the Nuclear Spectroscopic Telescope Array (NuSTAR) Explorer mission. We present laboratory measurement as well as flight data from the HEFT program that demonstrate the spectral resolution, imaging performance, quantum efficiency, and background levels achievable for balloon and space platforms using the HEFT/NuSTAR hybrid configuration.

  10. Suppressed blinking behavior of thioglycolic acid capped CdTe quantum dot by amine functionalization

    NASA Astrophysics Data System (ADS)

    Mandal, Abhijit; Tamai, Naoto

    2011-12-01

    Prepared water soluble thioglycolic acid capped CdTe quantum dots (QDs) were further surface functionalized by ethylene diamine (EDA). Amine functionalized CdTe QDs demonstrate enhanced luminescence intensity at ensemble measurements and suppressed luminescence intermittency behavior at the single molecule level. A clear decrease in the power law exponent for "on" time behavior is observed in amine modified CdTe QDs. Our results show that surface of CdTe QDs modified by EDA can lead to an important physical mechanism to enhance fluorescence intensity, reduce blinking, and increase photostability.

  11. Review of Photovoltaic Energy Production Using CdTe Thin-Film Modules: Extended Abstract Preprint

    SciTech Connect

    Gessert, T. A.

    2008-09-01

    CdTe has near-optimum bandgap, excellent deposition traits, and leads other technologies in commercial PV module production volume. Better understanding materials properties will accelerate deployment.

  12. Effects of CdTe growth conditions and techniques on the efficiency limiting defects and mechanisms in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Rohatgi, A.; Chou, H. C.; Jokerst, N. M.; Thomas, E. W.; Ferekides, C.; Kamra, S.; Feng, Z. C.; Dugan, K. M.

    1996-01-01

    CdTe solar cells were fabricated by depositing CdTe films on CdS/SnO2/glass substrates using close-spaced sublimation (CSS) and metalorganic chemical vapor deposition (MOCVD). Te/Cd mole ratio was varied in the range of 0.02 to 6 in the MOCVD growth ambient in an attempt to vary the native defect concentration. Polycrystalline CdTe layers grown by MOCVD and CSS both showed average grain size of about 2 μm. However, the CdTe films grown by CSS were found to be less faceted and more dense compared to the CdTe grown by MOCVD. CdTe growth techniques and conditions had a significant impact on the electrical characteristics of the cells. The CdTe solar cells grown by MOCVD in the Te-rich growth condition and by the CSS technique gave high cell efficiencies of 11.5% and 12.4%, respectively, compared to 6.6% efficient MOCVD cells grown in Cd-rich conditions. This large difference in efficiency is explained on the basis of (a) XRD measurements which showed a higher degree of atomic interdiffusion at the CdS/CdTe interface in high performance devices, (b) Raman measurements which endorsed more uniform and preferred grain orientation by revealing a sharp CdTe TO mode in the high efficiency cells, and (c) carrier transport mechanism which switched from tunneling/interface recombination to depletion region recombination in the high efficiency cells. In this study, Cu/Au layers were evaporated on CdTe for the back contact. Lower efficiency of the Te-rich MOCVD cells, compared to the CSS cells, was attributed to contact related additional loss mechanisms, such as Cd pile-up near Cu/CdTe interface which can give rise to Cd-vacancy defects in the bulk, and higher Cu concentration in the CdTe layer which can cause shunts in the device. Finally, SIMS measurements on the CdTe films of different crystallinity and grain size confirmed that grain boundaries are the main conduits for Cu migration into the CdTe film. Thus larger CdTe grain size or lower grain boundary area per unit volume

  13. Design and Performance of the Soft Gamma-ray Detector for the NeXT mission

    SciTech Connect

    Tajima, Hiroyasu; Kamae, T.; Madejski, G.; Mitani, T.; Nakazawa, K.; Tanaka, T.; Takahashi, T.; Watanabe, S.; Fukazawa, Y.; Ikagawa, T.; Kataoka, J.; Kokubun, M.; Makishima, K.; Terada, Y.; Nomachi, M.; Tashiro, M.; /SLAC /Sagamihara, Inst. Space Astron. Sci. /Tokyo U. /Hiroshima U. /Tokyo Inst. Tech. /Wako, RIKEN /Osaka U. /Saitama U.

    2006-04-19

    The Soft Gamma-ray Detector (SGD) on board the NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view (FOV), which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and CdTe (cadmium telluride) detectors. It can detect photons in a wide energy band (0.05-1 MeV) at a background level of 5 x 10{sup -7} counts/s/cm{sup 2}/keV; the silicon layers are required to improve the performance at a lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of the SGD, allowing it to achieve both high angular resolution and good background rejection capability. An additional capability of the SGD, its ability to measure gamma-ray polarization, opens up a new window to study properties of astronomical objects. We will present the development of key technologies to realize the SGD: high quality CdTe, low noise front-end ASIC and bump bonding technology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for Si strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.

  14. Design and performance of soft gamma-ray detector for NeXT mission

    SciTech Connect

    Tajima, H.; Kamae, T.; Madejski, G.; Takahashi, T.; Nakazawa, K.; Watanabe, S.; Mitani, T.; Tanaka, T.; Fukazawa, Y.; Kataoka, J.; Ikagawa, T.; Kokubun, M.; Makishima, K.; Terada, Y.; Nomachi, M.; Tashiro, M.; /Saitama U.

    2005-05-04

    The Soft Gamma-ray Detector (SGD) on board NeXT (Japanese future high energy astrophysics mission) is a Compton telescope with narrow field of view, which utilizes Compton kinematics to enhance its background rejection capabilities. It is realized as a hybrid semiconductor gamma-ray detector which consists of silicon and Cadmium Telluride (CdTe) detectors. It can detect photons in an energy band 0.05-1 MeV at a background level of 5 x 10{sup -7} counts/s/cm{sup 2}/keV; the silicon layers are required to improve the performance at a lower energy band (<0.3 MeV). Excellent energy resolution is the key feature of the SGD to achieve both high angular resolution and good background rejection capability. Its ability to measure gamma-ray polarization opens up a new window to study gamma-ray emission in the universe. We will present the development of key technologies to realize the SGD; high quality CdTe, low noise front-end VLSI and bump bonding technology. Energy resolutions of 1.7 keV (FWHM) for CdTe pixel detectors and 1.1 keV for silicon strip detectors have been measured. We also present the validation of Monte Carlo simulation used to evaluate the performance of the SGD.

  15. Transmutation detectors

    NASA Astrophysics Data System (ADS)

    Viererbl, L.; Lahodová, Z.; Klupák, V.; Sus, F.; Kučera, J.; Kůs, P.; Marek, M.

    2011-03-01

    We have designed a new type of detectors, called transmutation detectors, which can be used primarily for neutron fluence measurement. The transmutation detector method differs from the commonly used activation detector method in evaluation of detector response after irradiation. Instead of radionuclide activity measurement using radiometric methods, the concentration of stable non-gaseous nuclides generated by transmutation in the detector is measured using analytical methods like mass spectrometry. Prospective elements and nuclear reactions for transmutation detectors are listed and initial experimental results are given. The transmutation detector method could be used primarily for long-term measurement of neutron fluence in fission nuclear reactors, but in principle it could be used for any type of radiation that can cause transmutation of nuclides in detectors. This method could also be used for measurement in accelerators or fusion reactors.

  16. X-ray detector physics and applications; Proceedings of the Meeting, San Diego, CA, July 23, 24, 1992

    NASA Astrophysics Data System (ADS)

    Hoover, Richard B.

    1993-02-01

    Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)

  17. X-ray detector physics and applications; Proceedings of the Meeting, San Diego, CA, July 23, 24, 1992

    NASA Technical Reports Server (NTRS)

    Hoover, Richard B. (Editor)

    1993-01-01

    Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)

  18. Development and characterization of scintillation based detectors for the use in radiological early warning networks

    NASA Astrophysics Data System (ADS)

    Kessler, P.; Dombrowski, H.; Neumaier, S.

    2016-02-01

    To detect radiological incidents, all members of the European Union have installed nationwide radiological early warning networks. Most of the installed detector systems supply only dosimetric information. Novel spectrometry systems are considered to be good candidates for a new detector generation for environmental radiation monitoring because they will supply both nuclide-specific information and ambient dose equivalent rate values. Four different detector types were chosen and compared with each other (LaBr3, CeBr3, SrI2 scintillation detectors, and CdZnTe, a semiconductor detector). As a first step, the inherent background of these detectors was measured in the low background underground laboratory UDO II of PTB. As a second step, the relative detection sensitivity between the various detectors was determined at different energies. Finally, the detectors were exposed to a 4π-radiation field of radon progeny in PTB's radon chamber. The obtained results show that the investigated detectors are well suited for environmental radiation monitoring.

  19. Phosphorus Doping of Polycrystalline CdTe by Diffusion

    SciTech Connect

    Colegrove, Eric; Albin, David S.; Guthrey, Harvey; Harvey, Steve; Burst, James; Moutinho, Helio; Farrell, Stuart; Al-Jassim, Mowafak; Metzger, Wyatt K.

    2015-06-14

    Phosphorus diffusion in single crystal and polycrystalline CdTe material is explored using various methods. Dynamic secondary ion mass spectroscopy (SIMS) is used to determine 1D P diffusion profiles. A 2D diffusion model is used to determine the expected cross-sectional distribution of P in CdTe after diffusion anneals. Time of flight SIMS and cross-sectional cathodoluminescence corroborates expected P distributions. Devices fabricated with diffused P exhibit hole concentrations up to low 1015 cm-3, however a subsequent activation anneal enabled hole concentrations greater than 1016 cm-3. CdCl2 treatments and Cu based contacts were also explored in conjunction with the P doping process.

  20. DX centers in CdTe: a density functional study

    SciTech Connect

    Du, Mao-Hua

    2008-01-01

    DX centers induced by both group-III and group-VII donors in CdTe are studied using density functional calculations. The results show that, for group-VII donors, the DX centers with a cation-cation bond ({alpha}- and {beta}-CCB-DX centers) are more stable than the previously proposed broken-bond DX (BB-DX) center and the {beta}-CCB-DX center is the most stable. The stability trend found for the CCB-DX centers for different donors in CdTe is consistent with that for GaAs and GaSb, which suggests a general rule that the CCB-DX centers are favored for small donor atoms on anion site especially for semiconductors with large anion size.

  1. Dependence of CdTe response of bias history

    SciTech Connect

    Sites, J.R.; Sasala, R.A.; Eisgruber, I.L.

    1995-11-01

    Several time-dependent effect have been observed in CdTe cells and modules in recent years. Some appear to be related to degradation at the back contact, some to changes in temperature at the thin-film junction, and some to the bias history of the cell or module. Back-contact difficulties only occur in some cases, and the other two effects are reversible. Nevertheless, confusion in data interpretation can arise when these effects are not characterized. This confusion can be particularly acute when more than one time-dependent effect occurs during the same measurement cycle. The purpose of this presentation is to help categorize time-dependent effects in CdTe and other thin-film cells to elucidate those related to bias history, and to note differences between cell and module analysis.

  2. CdTe nanoparticles synthesized by laser ablation

    SciTech Connect

    Semaltianos, N. G.; Logothetidis, S.; Perrie, W.; Romani, S.; Potter, R. J.; Dearden, G.; Watkins, K. G.; Sharp, M.

    2009-07-20

    Nanoparticle generation by laser ablation of a solid target in a liquid environment is an easy, fast, and 'green' method for a large scale production of nanomaterials with tailored properties. In this letter we report the synthesis of CdTe nanoparticles by femtosecond laser [387 nm, 180 fs, 1 kHz, pulse energy=6 {mu}J (fluence=1.7 J/cm{sup 2})] ablation of the target material. Nanoparticles with diameters from {approx}2 up to {approx}25 nm were observed to be formed in the colloidal solution. Their size distribution follows the log-normal function with a statistical median diameter of {approx_equal}7.1 nm. Their crystal structure is the same as that of the bulk material (cubic zincblende) and they are slightly Cd-rich (Cd:Te percentage ratio {approx}1:0.9). Photoluminescence emission from the produced nanoparticles was detected in the deep red ({approx}652 nm)

  3. Chemical compatibility studies of GaAs and CdZnTe with the alloys WC-103 and TZM

    NASA Astrophysics Data System (ADS)

    Beske, S. A.; Arikawa, Y.; Andrews, R. N.; Lundblad, W.

    1994-03-01

    The objective of this study was to determine the chemical compatibility of gallium arsenide (GaAs) and cadmium zinc telluride (CdZnTe) with WC-103, a niobium hafnium titanium alloy, and TZM, a titanium zirconium molybdenum alloy. Compatibility in these systems is of primary interest for crystal growth experiments during space shuttle missions. Crystal growth ampoules containing GaAs and CdZnTe must be encased in a sample ampoule cartridge assembly (SACA) during crystal growth, which is qualified as a level of safety containment. Two of the primary metal candidates for these containment cartridges for experiments conducted aboard the USML-1 shuttle mission were WC-103 and TZM. Reaction couples between the semiconductors and the metals were constructed and used to simulate failure of the growth ampoule. Experiments were designed to examine various stages of failure including the worst case situation, in which failure occurred at the beginning of the growth experiment. The couples were analyzed optically and using the scanning electron microscope to evaluate any metal loss or reaction products formed.

  4. Development of a Method for Chemical-Mechanical Preparation of the Surface of CdZnTe Substrates for HgCdTe-Based Infrared Focal-Plane Arrays

    NASA Astrophysics Data System (ADS)

    Pelenc, D.; Merlin, J.; Etcheberry, A.; Ballet, P.; Baudry, X.; Brellier, D.; Destefanis, V.; Ferron, A.; Fougères, P.; Giotta, D.; Grangier, C.; Mollard, L.; Perez, A.; Rochette, F.; Rubaldo, L.; Vaux, C.; Vigneron, J.; Zanatta, J.-P.

    2014-08-01

    This paper reports the first implementation in our laboratory of a chemical-mechanical polishing (CMP) process for CdZnTe (CZT) substrates prepared for growth of HgCdTe layers by liquid phase epitaxy and molecular beam epitaxy. The process enables significant reduction of the thickness of the damaged zone induced by the mechanical polishing that must be etched away before epitaxy. Resulting improvements in surface morphology, in terms of waviness and density of point defects, are reported. The chemical state of surfaces polished by CMP was characterized by x-ray photoelectron spectroscopy. The chemical state was highly homogeneous; comparison with a reference surface is reported. End use assessment of this surface processing was compared with that of reference substrates by preparation of focal-plane arrays in the medium-wavelength infrared spectral range, by using epitaxial layers grown on substrates polished by different methods. The electro-optical performance of the detectors, in terms of photovoltaic noise operability, are reported. The results reveal that the state of this CMP surface is at the level of the best commercial substrates.

  5. CZT Virtual Frisch-grid Detector: Principles and Applications

    SciTech Connect

    Cui,Y.; Bolotnikov, A.; Camarda, G.; Hossain, A.; James, R. B.

    2009-03-24

    Cadmium Zinc Telluride (CdZnTe or CZT) is a very attractive material for using as room-temperature semiconductor detectors, because it has a wide bandgap and a high atomic number. However, due to the material's poor hole mobility, several special techniques were developed to ensure its suitability for radiation detection. Among them, the virtual Frisch-grid CZT detector is an attractive option, having a simple configuration, yet delivering an outstanding spectral performance. The goal of our group in Brookhaven National Laboratory (BNL) is to improve the performance of Frisch-ring CZT detectors; most recently, that effort focused on the non-contacting Frisch-ring detector, allowing us to build an inexpensive, large-volume detector array with high energy-resolution and a large effective area. In this paper, the principles of virtual Frisch-grid detectors are described, especially BNL's innovative improvements. The potential applications of virtual Frisch-grid detectors are discussed, and as an example, a hand-held gamma-ray spectrometer using a CZT virtual Frischgrid detector array is introduced, which is a self-contained device with a radiation detector, readout circuit, communication circuit, and high-voltage supply. It has good energy resolution of 1.4% (FWHM of 662-keV peak) with a total detection volume of {approx}20 cm{sup 3}. Such a portable inexpensive device can be used widely in nonproliferation applications, non-destructive detection, radiation imaging, and for homeland security. Extended systems based on the same technology have potential applications in industrial- and nuclear-medical-imaging.

  6. Optical modeling of graphene contacted CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Aldosari, Marouf; Sohrabpoor, Hamed; Gorji, Nima E.

    2016-04-01

    For the first time, an optical model is applied on CdS/CdTe thin film solar cells with graphene front or back contact. Graphene is highly conductive and is as thin as a single atom which reduces the light reflection and absorption, and thus enhances the light transmission to CdTe layer for a wide range of wavelengths including IR. Graphene as front electrode of CdTe devices led to loss in short circuit current density of 10% ΔJsc ≤ 15% compared to the conventional electrodes of TCO and ITO at CdS thickness of dCdS = 100 nm. In addition, all the multilayer graphene electrodes with 2, 4, and 7 graphene layers led to Jsc ≤ 20 mA/cm2. Therefore, we conclude that a single monolayer graphene with hexagonal carbon network reduces optical losses and enhances the carrier collection measured as Jsc. In another structure design, we applied the optical model to graphene back contacted CdS/CdTe device. This scheme allows double side irradiation of the cell which is expected to enhance the Jsc. We obtained 1 ∼ 6 , 23, and 38 mA/cm2 for back, front and bifacial illumination of graphene contacted CdTe cell with CdS = 100 nm. The bifacial irradiated cell, to be efficient, requires an ultrathin CdTe film with dCdTe ≤ 1 μm. In this case, the junction electric field extends to the back region and collects out the generated carriers efficiently. This was modelled by absorptivity rather than transmission rate and optical losses. Since the literature suggest that ZnO can increase the graphene conductivity and enhance the Jsc, we performed our simulations for a graphene/ZnO electrode (ZnO = 100 nm) instead of a single graphene layer.

  7. CdTe Feedstock Development and Validation: Cooperative Research and Development Final Report, CRADA Number CRD-08-00280

    SciTech Connect

    Albin, D.

    2011-05-01

    The goal of this work was to evaluate different CdTe feedstock formulations (feedstock provided by Redlen) to determine if they would significantly improve CdTe performance with ancillary benefits associated with whether changes in feedstock would affect CdTe cell processing and possibly reliability of cells. Feedstock also included attempts to intentionally dope the CdTe with pre-selected elements.

  8. Approaches to improve the Voc of CDTE devices: Device modeling and thinner devices, alternative back contacts

    NASA Astrophysics Data System (ADS)

    Walkons, Curtis J.

    An existing commercial process to develop thin film CdTe superstrate cells with a lifetime tau=1-3 ns results in Voc= 810-850 mV which is 350 mV lower than expected for CdTe with a bandgap EG = 1.5 eV. Voc is limited by 1.) SRH recombination in the space charge region; and 2.) the Cu2Te back contact to CdTe, which, assuming a 0.3 eV CdTe/Cu2Te barrier, exhibits a work function of phi Cu2Te= 5.5 eV compared to the CdTe valence band of Ev,CdTe=5.8 eV. Proposed solutions to develop CdTe devices with increased Voc are: 1.) reduce SRH recombination by thinning the CdTe layer to ≤ 1 mum; and 2.) develop an ohmic contact back contact using a material with phi BC≥5.8 eV. This is consistent with simulations using 1DSCAPS modeling of CdTe/CdS superstrate cells under AM 1.5 conditions. Two types of CdTe devices are presented. The first type of CdTe device utilizes a window/CdTe stack device with an initial 3-9 mum CdTe layer which is then chemically thinned resulting in regions of the CdTe film with thickness less than 1 mum. The CdTe surface was contacted with a liquid junction quinhydrone-Pt (QH-Pt) probe which enables rapid repeatable Voc measurements on CdTe before and after thinning. In four separate experiments, the window/CdTe stack devices with thinned CdTe exhibited a Voc increase of 30-170 mV, which if implemented using a solid state contact could cut the Voc deficit in half. The second type of CdTe device utilizes C61 PCBM as a back contact to the CdTe, selected since PCBM has a valence band maximum energy (VBM) of 5.8 eV. The PCBM films were grown by two different chemistries and the characterization of the film properties and device results are discussed. The device results show that PCBM exhibits a blocking contact with a 0.6 eV Schottky barrier and possible work function of phiPCBM = 5.2 eV.

  9. Single-Crystal CdTe Homojunction Structures for Solar Cell Applications

    NASA Astrophysics Data System (ADS)

    Su, Peng-Yu; Dahal, Rajendra; Wang, Gwo-Ching; Zhang, Shengbai; Lu, Toh-Ming; Bhat, Ishwara B.

    2015-09-01

    We report two different CdTe homojunction solar cell structures. Single-crystal CdTe homojunction solar cells were grown on GaAs single-crystal substrates by metalorganic chemical vapor deposition. Arsenic and iodine were used as dopants for p-type and n-type CdTe, respectively. Another homojunction solar cell structure was fabricated by growing n-type CdTe directly on bulk p-type CdTe single-crystal substrates. The electrical properties of the different layers were characterized by Hall measurements. When arsine was used as arsenic source, the highest hole concentration was ~6 × 1016 cm-3 and the activation efficiency was ~3%. Very abrupt arsenic doping profiles were observed by secondary ion mass spectrometry. For n-type CdTe with a growth temperature of 250°C and a high Cd/Te ratio the electron concentration was ~4.5 × 1016 cm-3. Because of the 300 nm thick n-type CdTe layer, the short circuit current of the solar cell grown on the bulk CdTe substrate was less than 10 mA/cm2. The open circuit voltage of the device was 0.86 V. According to a prediction based on measurement of short circuit current density ( J sc) as a function of open circuit voltage ( V oc), an open circuit voltage of 0.92 V could be achieved by growing CdTe solar cells on bulk CdTe substrates.

  10. Material uniformity of CdZnTe grown by low-pressure bridgman

    NASA Astrophysics Data System (ADS)

    Greaves, C. M.; Brunett, B. A.; Van Scyoc, J. M.; Schlesinger, T. E.; James, R. B.

    2001-02-01

    We have employed Low-Temperature Photoluminescence (LTPL) and Room-Temperature Photoluminescence Mapping (RTPLM) to explore the crystalline quality and material uniformity of Cadmium Zinc Telluride (CZT) radiation detector material grown by the Low-Pressure Bridgman (LPB) technique. We report on the differences in crystalline quality and uniformity of material supplied by eV Products Inc. and IMARAD Imaging Systems Ltd. In addition, we have examined the general detector response of the material supplied by IMARAD. We report on the uniformity of the detector response and the temperature dependence of this response when used as a detector.

  11. X-ray irradiation effects on the trapping properties of Cd{sub 1-x}Zn{sub x}Te detectors

    SciTech Connect

    Fraboni, B.; Pasquini, L.; Castaldini, A.; Cavallini, A.

    2009-11-01

    CdZnTe-based detectors possess unique properties as room-temperature x- and gamma-ray detectors. We report on the effects of x-ray irradiation on CdZnTe and CdTe:Cl detectors with increasing x-ray doses. We correlate the 'macroscopic' performance of the detectors, investigated by gamma-ray spectroscopy to the 'microscopic' effects induced by the impinging radiation, i.e., the defective states introduced in the crystal lattice. The electrical activity of the defects and their activation energy have been investigated by photo induced current transient spectroscopy and by space charge limited current analyses. We identify the x-ray dose that induces a significant degradation in the detector performance, and by cross-correlating the results obtained, we achieve a reliable estimate of the actual concentration of electrically active deep states and assess the potentiality of these experimental methods as tools for quantitative analyses of high resistivity materials.

  12. The High Energy Detector of Simbol-X

    SciTech Connect

    Meuris, A.; Limousin, O.; Blondel, C.; Le Mer, I.; Pinsard, F.; Cara, C.; Goetschy, A.; Martignac, J.; Laurent, P.; Chipaux, R.; Rio, Y.; Fontignie, J.; Horeau, B.; Ferrando, P.; Lugiez, F.; Gevin, O.; Tauzin, G.; Herve, S.; Authier, M.

    2009-05-11

    The High Energy Detector (HED) is one of the three detection units on board the Simbol-X detector spacecraft. It is placed below the Low Energy Detector so as to collect focused photons in the energy range from 8 to 80 keV. It consists of a mosaic of 64 independent cameras, divided in 8 sectors. Each elementary detection unit, called Caliste, is the hybridization of a 256-pixel Cadmium Telluride (CdTe) detector with full custom front-end electronics into a unique component. The status of the HED design will be reported. The promising results obtained from the first micro-camera prototypes called Caliste 64 and Caliste 256 will be presented to illustrate the expected performance of the instrument.

  13. Growth of CdTe thin films on graphene by close-spaced sublimation method

    SciTech Connect

    Jung, Younghun; Yang, Gwangseok; Kim, Jihyun; Chun, Seungju; Kim, Donghwan

    2013-12-02

    CdTe thin films grown on bi-layer graphene were demonstrated by using the close-spaced sublimation method, where CdTe was selectively grown on the graphene. The density of the CdTe domains was increased with increasing the number of the defective sites in the graphene, which was controlled by the duration of UV exposure. The CdTe growth rate on the bi-layer graphene electrodes was 400 nm/min with a bandgap energy of 1.45–1.49 eV. Scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence, and X-ray diffraction technique were used to confirm the high quality of the CdTe thin films grown on the graphene electrodes.

  14. Synthesis and characterization of high-ordered CdTe nanorods

    NASA Astrophysics Data System (ADS)

    Ma, Ligang; Wei, Zelu; Zhang, Fengming; Wu, Xiaoshan

    2015-12-01

    Cadmium telluride (CdTe) materials are an important absorbed layer and development solar energy conversion devices based on nano-fabrication techniques have attracted considerable interest in fabricating optoelectronic devices. Herein, through close-space sublimation method, vertically high-aligned CdTe nanorods are successfully obtained for the first time, with the help of Anodic Aluminum Oxide (AAO) template, which can perfectly control the morphology, diameter, and spacing among the CdTe nanorods. Its the crystal structure and optical properties are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, and photoluminescence. The results indicate that CdTe nanorods are textured polycrystalline with the cubic phase and bear good crystallinity. In addition, this deposition technique is a clean, inexpensive, high-throughput, versatile and reproducible for obtaining vertically aligned CdTe nanorod, which shows the potential applications in the future for the preparation of CdTe-based nanostructure solar cells.

  15. Molecular Dynamics Studies of Dislocations in CdTe Crystals from a New Bond Order Potential.

    PubMed

    Zhou, Xiaowang; Ward, Donald K; Wong, Bryan M; Doty, F Patrick; Zimmerman, Jonathan A

    2012-08-23

    Cd(1-x)Zn(x)Te (CZT) crystals are the leading semiconductors for radiation detection, but their application is limited by the high cost of detector-grade materials. High crystal costs primarily result from property nonuniformity that causes low manufacturing yield. Although tremendous efforts have been made in the past to reduce Te inclusions/precipitates in CZT, this has not resulted in an anticipated improvement in material property uniformity. Moreover, it is recognized that in addition to Te particles, dislocation cells can also cause electric field perturbations and the associated property nonuniformities. Further improvement of the material, therefore, requires that dislocations in CZT crystals be understood and controlled. Here, we use a recently developed CZT bond order potential to perform representative molecular dynamics simulations to study configurations, energies, and mobilities of 29 different types of possible dislocations in CdTe (i.e., x = 1) crystals. An efficient method to derive activation free energies and activation volumes of thermally activated dislocation motion will be explored. Our focus gives insight into understanding important dislocations in the material and gives guidance toward experimental efforts for improving dislocation network structures in CZT crystals.

  16. Influence of EDTA{sup 2-} on the hydrothermal synthesis of CdTe nanocrystallites

    SciTech Connect

    Gong Haibo; Hao Xiaopeng; Xu Xiangang

    2011-12-15

    Transformation from Te nanorods to CdTe nanoparticles was achieved with the assistance of EDTA as a ligand under hydrothermal conditions. Experimental results showed that at the beginning of reaction Te nucleated and grew into nanorods. With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. Finally, nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were obtained. The effects of EDTA on the morphology and formation of CdTe nanoparticles were discussed in consideration of the strong ligand-effect of EDTA, which greatly decreased the concentration of Cd{sup 2+}. Furthermore, the possible formation process of CdTe nanoparticles from Te nanorods was further proposed. The crystal structure and morphology of the products were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). - Graphical Abstract: Firstly, Te nucleated and grew into nanorods in the presence of EDTA{sup 2-}. Then CdTe nucleus began to emerge on Te nanorods and finally monodispersed CdTe nanoparticles were obtained. Highlights: Black-Right-Pointing-Pointer EDTA serves as a strong ligand with Cd{sup 2+}. Black-Right-Pointing-Pointer The existence of EDTA constrains the nucleation of CdTe and promotes the formation of Te nanorods. Black-Right-Pointing-Pointer With the proceeding of reaction, CdTe nucleus began to emerge on the surface, especially on the tips of Te nanorods. Black-Right-Pointing-Pointer Nearly monodispersed hexagonal CdTe nanoparticles with diameters of about 200 nm were finally obtained.

  17. Te Inclusions in CZT Detectors: New Method for Correcting Their Adverse Effects

    SciTech Connect

    Bolotnikov, A.E.; Babalola, S.; Camarda, G.S.; Cui, Y.; Egarievwe, S.U.; Hawrami, R.; Hossain, A.; Yang, G.; James, R.B.

    2009-10-25

    Both Te inclusions and point defects can trap the charge carriers generated by ionizing particles in CdZnTe (CZT) detectors. The amount of charge trapped by point defects is proportional to the carriers’ drift time and can be corrected electronically. In the case of Te inclusions, the charge loss depends upon their random locations with respect to the electron cloud. Consequently, inclusions introduce fluctuations in the charge signals, which cannot be easily corrected. In this paper, we describe direct measurements of the cumulative effect of Te inclusions and its influence on the response of CZT detectors of different thicknesses and different sizes and concentrations of Te inclusions. We also discuss a means of partially correcting their adverse effects.

  18. Charge Sharing and Charge Loss in a Cadmium-Zinc-Telluride Fine-Pixel Detector Array

    NASA Technical Reports Server (NTRS)

    Gaskin, J. A.; Sharma, D. P.; Ramsey, B. D.; Six, N. Frank (Technical Monitor)

    2002-01-01

    Because of its high atomic number, room temperature operation, low noise, and high spatial resolution a Cadmium-Zinc-Telluride (CZT) multi-pixel detector is ideal for hard x-ray astrophysical observation. As part of on-going research at MSFC (Marshall Space Flight Center) to develop multi-pixel CdZnTe detectors for this purpose, we have measured charge sharing and charge loss for a 4x4 (750micron pitch), lmm thick pixel array and modeled these results using a Monte-Carlo simulation. This model was then used to predict the amount of charge sharing for a much finer pixel array (with a 300micron pitch). Future work will enable us to compare the simulated results for the finer array to measured values.

  19. Smoke Detector

    NASA Technical Reports Server (NTRS)

    1979-01-01

    In the photo, Fire Chief Jay Stout of Safety Harbor, Florida, is explaining to young Richard Davis the workings of the Honeywell smoke and fire detector which probably saved Richard's life and that of his teen-age brother. Alerted by the detector's warning, the pair were able to escape their burning home. The detector in the Davis home was one of 1,500 installed in Safety Harbor residences in a cooperative program conducted by the city and Honeywell Inc.

  20. Degradation and capacitance: voltage hysteresis in CdTe devices

    NASA Astrophysics Data System (ADS)

    Albin, D. S.; Dhere, R. G.; Glynn, S. C.; del Cueto, J. A.; Metzger, W. K.

    2009-08-01

    CdS/CdTe photovoltaic solar cells were made on two different transparent conducting oxide (TCO) structures in order to identify differences in fabrication, performance, and reliability. In one set of cells, chemical vapor deposition (CVD) was used to deposit a bi-layer TCO on Corning 7059 borosilicate glass consisting of a F-doped, conductive tin-oxide (cSnO2) layer capped by an insulating (undoped), buffer (iSnO2) layer. In the other set, a more advanced bi-layer structure consisting of sputtered cadmium stannate (Cd2SnO4; CTO) as the conducting layer and zinc stannate (Zn2SnO4; ZTO) as the buffer layer was used. CTO/ZTO substrates yielded higher performance devices however performance uniformity was worse due to possible strain effects associated with TCO layer fabrication. Cells using the SnO2-based structure were only slightly lower in performance, but exhibited considerably greater performance uniformity. When subjected to accelerated lifetime testing (ALT) at 85 - 100 °C under 1-sun illumination and open-circuit bias, more degradation was observed in CdTe cells deposited on the CTO/ZTO substrates. Considerable C-V hysteresis, defined as the depletion width difference between reverse and forward direction scans, was observed in all Cu-doped CdTe cells. These same effects can also be observed in thin-film modules. Hysteresis was observed to increase with increasing stress and degradation. The mechanism for hysteresis is discussed in terms of both an ionic-drift model and one involving majority carrier emission in the space-charge region (SCR). The increased generation of hysteresis observed in CdTe cells deposited on CTO/ZTO substrates suggests potential decomposition of these latter oxides when subjected to stress testing.

  1. Study of tellurium precipitates in CdTe crystals

    NASA Technical Reports Server (NTRS)

    Jayatirtha, H. N.; Henderson, D. O.; Burger, A.; Volz, M. P.

    1993-01-01

    The effect of tellurium precipitates was studied in medium resistivity (10 exp 3-10 exp 6 ohm cm) undoped and Cl-doped CdTe using differential scanning calorimetry (DSC) and mid-infrared spectroscopy and the results were correlated with near-infrared microscopy photographs. When present in a significant quantity (about 0.25 wt pct), we show that Te precipitates are detectable using DSC measurements. In the mid-infrared, the contribution of the absorption by free-carriers is negligible, and therefore, the effect of the Te precipitates in these crystals can be considered uncoupled from the effects of Cd vacancies.

  2. High-Efficiency, Commercial Ready CdTe Solar Cells

    SciTech Connect

    Sites, James R.

    2015-11-19

    Colorado State’s F-PACE project explored several ways to increase the efficiency of CdTe solar cells and to better understand the device physics of those cells under study. Increases in voltage, current, and fill factor resulted in efficiencies above 17%. The three project tasks and additional studies are described in detail in the final report. Most cells studied were fabricated at Colorado State using an industry-compatible single-vacuum closed-space-sublimation (CSS) chamber for deposition of the key semiconductor layers. Additionally, some cells were supplied by First Solar for comparison purposes, and a small number of modules were supplied by Abound Solar.

  3. Growth kinetics of CdTe colloidal nanocrystals.

    PubMed

    Ferreira, D Lourençoni; Silva, F Oliveira; Viol, L Cristina de Souza; Licínio, P; Valadares, M; Cury, L Alberto; Schiavon, M Antônio; Alves, J Luiz Aarestrup

    2009-08-28

    The growth kinetics of CdTe colloidal nanocrystals has been analyzed quantitatively by means of dynamic light scattering and photoluminescence measurements. The growth rates, size distributions, critical radii, and diffusion constants have been calculated in the framework of the Sugimoto theoretical model. A two-step diffusion-controlled growth regime has been proposed for the reported synthesis and a set of relations for the time evolution of the size distribution has been derived and discussed in the sense of the size distribution focusing concept. PMID:19725626

  4. Raman characterization of a new Te-rich binary compound: CdTe2.

    PubMed

    Rousset, Jean; Rzepka, Edouard; Lincot, Daniel

    2009-04-01

    Structural characterization by Raman spectroscopy of CdTe thin films electrodeposited in acidic conditions is considered in this work. This study focuses on the evolution of material properties as a function of the applied potential and the film thickness, demonstrating the possibility to obtain a new Te-rich compound with a II/VI ratio of 1/2 under specific bath conditions. Raman measurements carried out on etched samples first allow the elimination of the assumption of a mixture of phases CdTe + Te and tend to confirm the formation of the CdTe(2) binary compound. The signature of this phase on the Raman spectrum is the increase of the LO band intensity compared to that obtained for the CdTe. The influence of the laser power is also considered. While no effect is observed on CdTe films, the increase of the incident irradiation power leads to the decomposition of the CdTe(2) compound into two more stable phases namely CdTe and Te.

  5. Dawn's Gamma Ray and Neutron Detector

    NASA Astrophysics Data System (ADS)

    Prettyman, Thomas H.; Feldman, William C.; McSween, Harry Y.; Dingler, Robert D.; Enemark, Donald C.; Patrick, Douglas E.; Storms, Steven A.; Hendricks, John S.; Morgenthaler, Jeffery P.; Pitman, Karly M.; Reedy, Robert C.

    2011-12-01

    The NASA Dawn Mission will determine the surface composition of 4 Vesta and 1 Ceres, providing constraints on their formation and thermal evolution. The payload includes a Gamma Ray and Neutron Detector (GRaND), which will map the surface elemental composition at regional spatial scales. Target elements include the constituents of silicate and oxide minerals, ices, and the products of volcanic exhalation and aqueous alteration. At Vesta, GRaND will map the mixing ratio of end-members of the howardite, diogenite, and eucrite (HED) meteorites, determine relative proportions of plagioclase and mafic minerals, and search for compositions not well sampled by the meteorite collection. The large south polar impact basin may provide an opportunity to determine the composition of Vesta’s mantle and lower crust. At Ceres, GRaND will provide chemical information needed to test different models of Ceres’ origin and thermal and aqueous evolution. GRaND is also sensitive to hydrogen layering and can determine the equivalent H2O/OH content of near-surface hydrous minerals as well as the depth and water abundance of an ice table, which may provide information about the state of water in the interior of Ceres. Here, we document the design and performance of GRaND with sufficient detail to interpret flight data archived in the Planetary Data System, including two new sensor designs: an array of CdZnTe semiconductors for gamma ray spectroscopy, and a loaded-plastic phosphor sandwich for neutron spectroscopy. An overview of operations and a description of data acquired from launch up to Vesta approach is provided, including annealing of the CdZnTe sensors to remove radiation damage accrued during cruise. The instrument is calibrated using data acquired on the ground and in flight during a close flyby of Mars. Results of Mars flyby show that GRaND has ample sensitivity to meet science objectives at Vesta and Ceres. Strategies for data analysis are described and prospective results

  6. Nonstoichiometric composition shift in physical vapor deposition of CdTe thin films

    NASA Astrophysics Data System (ADS)

    Chin, Ken K.; Cheng, Zimeng; Delahoy, Alan E.

    2015-05-01

    While it is being debated whether Cd vacancy is an effective p-dopant in CdTe, and whether CdTe thin film in solar energy application should be Cd-deficient or Cd-rich, in the theory of CdTe physical vapor deposition (PVD) it has been assumed that both the source material and the thin film product is stoichiometric. To remediate the lack of effective theory, a new PVD model for CdTe photovoltaic (PV) modules is presented in this work, in which the composition of the CdTe thin film under growth is a parameter determined by the source CdTe composition as well as the growth condition. The solid phase Cd1-δTe1+δ compound under deposition temperature is treated as a solid solution with a mole of excess pure Te or Cd as solute and one mole of congruently grown CdTe as solvent. Assuming that the vapor pressure of Te2 can be calculated by using the law of solid solution PTe=H0+aH1+a2H2 round the congruent composition, where the molar number a and the constants H0, H1 and H2 as functions of temperature T are extracted from the experimental data. Thus, the mole fraction of solute in the grown CdTe thin film as well as the growth rate, as a function of the solute mole fraction in the source CdTe can be determined.

  7. Optical Detectors

    NASA Astrophysics Data System (ADS)

    Goushcha, Alexander; Tabbert, Bernd

    Optical detectors are applied in all fields of human activities - from basic research to commercial applications in communication, automotive, medical imaging, homeland security, and other fields. The processes of light interaction with matter described in other chapters of this handbook form the basis for understanding the optical detectors physics and device properties.

  8. Optical Detectors

    NASA Astrophysics Data System (ADS)

    Tabbert, Bernd; Goushcha, Alexander

    Optical detectors are applied in all fields of human activities from basic research to commercial applications in communication, automotive, medical imaging, homeland security, and other fields. The processes of light interaction with matter described in other chapters of this handbook form the basis for understanding the optical detectors physics and device properties.

  9. Deposition of Hydrogenated Microcrystalline Films of CdTe by Chemical Sputtering in Hydrogen

    NASA Astrophysics Data System (ADS)

    Saito, Koji; Nishibayashi, Yoshiki; Imura, Takeshi; Osaka, Yukio

    1988-07-01

    Films of CdTe are deposited by chemical sputtering of a CdTe target in hydrogen gas. X-ray diffraction patterns show that the films are composed of microcrystals of cubic CdTe with a grain size of 15˜30 nm. The films contain a trace amount of hydrogen in the form of the Cd-H (and presumably Te-H2) bonds. This hydrogen is evolved during the thermal treatment of the film above 100°C, as the grain size of the microcrystal grows. The deposition rate is also reduced when the substrate temperature increases up to 100°C or more.

  10. Thin-film CdTe and CuInSe{sub 2} photovoltaic technologies

    SciTech Connect

    Ullal, H S; Zweibel, K; von Roedern, B G

    1993-08-01

    Total-area conversion efficiency of 15%--15.8% have been achieved for thin-film CdTe and CIS solar cells. Modules with power output of 5--53 W have been demonstrated by several groups world-wide. Critical processes and reaction pathways for achieving excellent PV devices have been eluciated. Research, development and technical issues have been identified, which could result in potential improvements in device and module performance. A 1-kW thin-film CdTe array has been installed and is being tested. Multimegawatt thin-film CdTe manufacturing plants are expected to be completed in 1-2 years.

  11. Effect of low energy ion irradiation on CdTe crystals: Luminescence enhancement

    SciTech Connect

    Olvera, J.; Plaza, J. L.; Dios, S. de; Dieguez, E.; Martinez, O.; Avella, M.

    2010-12-15

    In this work we show that low energy ion sputtering is a very efficient technique as a cleaning process for CdTe substrates. We demonstrate, by using several techniques like grazing-angle x-ray diffraction, cathodoluminescence, microluminescence, and micro-Raman spectroscopy that the luminescent properties of CdTe substrates can be very much increased when CdTe surfaces are irradiated with low energy Argon ions. We postulate that this enhancement is mainly due to the removal of surface damage induced by the cutting and polishing processes. The formation of a low density of nonluminescent aggregates after the sputtering process has also been observed.

  12. The development of 3rd generation IR detectors at AIM

    NASA Astrophysics Data System (ADS)

    Ziegler, J.; Eich, D.; Mahlein, M.; Schallenberg, T.; Scheibner, R.; Wendler, J.; Wenisch, J.; Wollrab, R.; Daumer, V.; Rehm, R.; Rutz, F.; Walther, M.

    2011-06-01

    3rd generation IR modules - dual-color (DC), dual-band (DB), and large format two-dimensional arrays - require sophisticated production technologies such as molecular beam epitaxy (MBE) as well as new array processing techniques, which can satisfy the rising demand for increasingly complex device structures and low cost detectors. AIM will extend its future portfolio by high performance devices which make use of these techniques. The DC MW / MW detectors are based on antimonide type-II superlattices (produced by MBE at Fraunhofer IAF, Freiburg) in the 384x288 format with a 40 μm pitch. For AIM, the technology of choice for MW / LW DB FPAs is MCT MBE on CdZnTe substrates, which has been developed in cooperation with IAF, Freiburg. 640x512, 20 μm pitch Focal Plane Arrays (FPAs) have been processed at AIM. The growth of MW MCT MBE layers on alternate substrates is challenging, but essential for competitive fabrication of large two-dimensional arrays such as megapixel (MW 1280x1024, 15 μm pitch) FPAs. This paper will present the development status and latest results of the above-mentioned 3rd Gen FPAs and Integrated Detector Cooler Assemblies (IDCAs).

  13. Apparent quantum efficiency effects in CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Gloeckler, M.; Sites, J. R.

    2004-04-01

    Quantum efficiency measurements of n-CdS/p-CdTe solar cells performed under nonstandard illumination, voltage bias, or both can be severely distorted by photogeneration and contact-barrier effects. In this work we will discuss the effects that are typically observed, the requirements needed to reproduce these effects with modeling tools, and the potential applications of apparent quantum efficiency analysis. Recently published experimental results are interpreted and reproduced using numerical simulation tools. The suggested model explains large negative apparent quantum efficiencies (≫100%) seen in the spectral range of 350-550 nm, modestly large negative apparent quantum efficiencies (>100%) in the spectral range of 800-850 nm, enhanced positive or negative response observed under red, blue, and white light bias, and photocurrent gain significantly different from unity. Some of these effects originate from the photogeneration in the highly compensated CdS window layer, some from photogeneration within the CdTe, and some are further modified by the height of the CdTe back-contact barrier.

  14. Advanced CdTe Photovoltaic Technology: September 2007 - March 2009

    SciTech Connect

    Barth, K.

    2011-05-01

    During the last eighteen months, Abound Solar (formerly AVA Solar) has enjoyed significant success under the SAI program. During this time, a fully automated manufacturing line has been developed, fabricated and commissioned in Longmont, Colorado. The facility is fully integrated, converting glass and semiconductor materials into complete modules beneath its roof. At capacity, a glass panel will enter the factory every 10 seconds and emerge as a completed module two hours later. This facility is currently undergoing trials in preparation for large volume production of 120 x 60 cm thin film CdTe modules. Preceding the development of the large volume manufacturing capability, Abound Solar demonstrated long duration processing with excellent materials utilization for the manufacture of high efficiency 42 cm square modules. Abound Solar prototype modules have been measured with over 9% aperture area efficiency by NREL. Abound Solar demonstrated the ability to produce modules at industry leading low costs to NREL representatives. Costing models show manufacturing costs below $1/Watt and capital equipment costs below $1.50 per watt of annual manufacturing capacity. Under this SAI program, Abound Solar supported a significant research and development program at Colorado State University. The CSU team continues to make progress on device and materials analysis. Modeling for increased device performance and the effects of processing conditions on properties of CdTe PV were investigated.

  15. Single CdTe Nanowire Optical Correlator for Femtojoule Pulses.

    PubMed

    Xin, Chenguang; Yu, Shaoliang; Bao, Qingyang; Wu, Xiaoqin; Chen, Bigeng; Wang, Yipei; Xu, Yingxin; Yang, Zongyin; Tong, Limin

    2016-08-10

    On the basis of the transverse second harmonic generation (TSHG) in a highly nonlinear subwavelength-diameter CdTe nanowire, we demonstrate a single-nanowire optical correlator for femto-second pulse measurement with pulse energy down to femtojoule (fJ) level. Pulses to be measured were equally split and coupled into two ends of a suspending nanowire via tapered optical fibers. The couterpropagating pulses meet each other around the central area of the nanowire, and emit TSHG signal perpendicular to the axis of the nanowire. By transferring the spatial intensity profile of the transverse second harmonic (TSH) image into the time-domain temporal profile of the input pulses, we operate the nanowire as a miniaturized optical correlator. Benefitted from the high nonlinearity and the very small effective mode area of the waveguiding CdTe nanowire, the input energy of the single-nanowire correlator can go down to fJ-level (e.g., 2 fJ/pulse for 1064 nm 200 fs pulses). The miniature fJ-pulse correlator may find applications from low power on-chip optical communication, biophotonics to ultracompact laser spectroscopy. PMID:27414182

  16. High Resolution X-ray Diffraction Studies of MBE-Grown HgCdTe Layers on Bulk-Grown CdZnTe Substrate

    NASA Astrophysics Data System (ADS)

    Amarasinghe, Priyanthi M.; Qadri, Syed B.; Wijewarnasuriya, Priyalal S.

    2015-08-01

    The structural properties of molecular beam epitaxially (MBE)-grown Hg1- x Cd x Te epilayers on CdZnTe (211) substrate have been investigated using high-resolution x-ray topography and rocking curves. High-resolution x-ray diffraction 2 θ- θ scans of (422) reflections were utilized in calculating the out-of-plane lattice parameters of the HgCdTe layer and the CdZnTe substrate. The lattice strain of the HgCdTe layer was evaluated using the in-plane measurements of the (311) reflection. Etching seemed to improve the surface of the substrate by removing any damage caused by polishing or any post-processing. In spite of some localized line dislocations, a remarkable quality of the MBE-grown HgCdTe layer was observed. The full width at half maximum values of the HgCdTe layer and the CdZnTe substrate were determined as 43 arc-s and 16.2 arc-s, respectively.

  17. Infrared Attenuation Spectrum of Bulk High-Resistivity CdZnTe Single Crystal in Transparent Wavelength Region Between Electronic and Lattice Absorptions

    NASA Astrophysics Data System (ADS)

    Sarugaku, Yuki; Kaji, Sayumi; Ikeda, Yuji; Kobayashi, Naoto; Sukegawa, Takashi; Nakagawa, Takao; Kataza, Hirokazu; Kondo, Sohei; Yasui, Chikako; Nakanishi, Kenshi; Kawakita, Hideyo

    2016-09-01

    We report measurement of the internal attenuation coefficient, α _{att} , of a bulk high-resistivity cadmium zinc telluride (CdZnTe) single crystal at wavelength, λ = 0.84-26 μ m, to the unprecedentedly low level of α _{att} ˜ 0.001 cm^{-1} . This measurement reveals the spectral behavior for small attenuation in the infrared transparent region between the electronic and lattice absorptions. This result is essential for application of CdZnTe as an infrared transmitting material. Comparing the attenuation spectrum with model spectra obtained on the basis of Mie theory, we find that sub-micrometer-sized Te particles (inclusions) with a number density of approximately 10^{7.5-9} cm^{-3} are the principal source of the small attenuation observed at λ = 0.9-13 μ m. In addition, we determine α _{att} = (7.7 ± 1.9) × 10^{-4} cm^{-1} at λ = 10.6 μ m, which is valuable for CO_2 laser applications. Higher transparency can be achieved by reducing the number of inclusions rather than the number of precipitates. This study also demonstrates that high-accuracy measurement of CdZnTe infrared transmittance is a useful approach to investigating the number density of sub-micrometer-sized Te particles that cannot be identified via infrared microscopy.

  18. Gaseous Detectors

    NASA Astrophysics Data System (ADS)

    Titov, Maxim

    Since long time, the compelling scientific goals of future high-energy physics experiments were a driving factor in the development of advanced detector technologies. A true innovation in detector instrumentation concepts came in 1968, with the development of a fully parallel readout for a large array of sensing elements - the Multi-Wire Proportional Chamber (MWPC), which earned Georges Charpak a Nobel prize in physics in 1992. Since that time radiation detection and imaging with fast gaseous detectors, capable of economically covering large detection volumes with low mass budget, have been playing an important role in many fields of physics. Advances in photolithography and microprocessing techniques in the chip industry during the past decade triggered a major transition in the field of gas detectors from wire structures to Micro-Pattern Gas Detector (MPGD) concepts, revolutionizing cell-size limitations for many gas detector applications. The high radiation resistance and excellent spatial and time resolution make them an invaluable tool to confront future detector challenges at the next generation of colliders. The design of the new micro-pattern devices appears suitable for industrial production. Novel structures where MPGDs are directly coupled to the CMOS pixel readout represent an exciting field allowing timing and charge measurements as well as precise spatial information in 3D. Originally developed for the high-energy physics, MPGD applications have expanded to nuclear physics, photon detection, astroparticle and neutrino physics, neutron detection, and medical imaging.

  19. The Dosepix detector—an energy-resolving photon-counting pixel detector for spectrometric measurements

    NASA Astrophysics Data System (ADS)

    Zang, A.; Anton, G.; Ballabriga, R.; Bisello, F.; Campbell, M.; Celi, J. C.; Fauler, A.; Fiederle, M.; Jensch, M.; Kochanski, N.; Llopart, X.; Michel, N.; Mollenhauer, U.; Ritter, I.; Tennert, F.; Wölfel, S.; Wong, W.; Michel, T.

    2015-04-01

    The Dosepix detector is a hybrid photon-counting pixel detector based on ideas of the Medipix and Timepix detector family. 1 mm thick cadmium telluride and 300 μm thick silicon were used as sensor material. The pixel matrix of the Dosepix consists of 16 x 16 square pixels with 12 rows of (200 μm)2 and 4 rows of (55 μm)2 sensitive area for the silicon sensor layer and 16 rows of pixels with 220 μm pixel pitch for CdTe. Besides digital energy integration and photon-counting mode, a novel concept of energy binning is included in the pixel electronics, allowing energy-resolved measurements in 16 energy bins within one acquisition. The possibilities of this detector concept range from applications in personal dosimetry and energy-resolved imaging to quality assurance of medical X-ray sources by analysis of the emitted photon spectrum. In this contribution the Dosepix detector, its response to X-rays as well as spectrum measurements with Si and CdTe sensor layer are presented. Furthermore, a first evaluation was carried out to use the Dosepix detector as a kVp-meter, that means to determine the applied acceleration voltage from measured X-ray tubes spectra.

  20. Dynamic Curvature and Stress Studies for MBE CdTe on Si and GaAs Substrates

    NASA Astrophysics Data System (ADS)

    Jacobs, R. N.; Jaime Vasquez, M.; Lennon, C. M.; Nozaki, C.; Almeida, L. A.; Pellegrino, J.; Arias, J.; Taylor, C.; Wissman, B.

    2015-09-01

    Infrared focal plane arrays (IRFPA) based on HgCdTe semiconductor alloys have been shown to be ideal for tactical and strategic applications. High density (>1 M pixel), high operability HgCdTe detectors on large area, low-cost composite substrates, such as CdTe-buffered Si or GaAs, are envisioned for next-generation IRFPAs. Thermal expansion mismatch is among various material parameters that govern the structural properties of the final detector layer. It has previously been shown that thermal expansion mismatch plays the dominant role in the residual stress characteristics of these heteroepitaxial structures (Jacobs et al. in J Electron Mater 37:1480, 2008). The wafer curvature (bowing) resulting from residual stress, is a likely source of problems that may occur during subsequent processing. This includes cracking of the film and substrate during post-growth annealing processes or even certain characterization techniques. In this work, we examine dynamic curvature and stress during molecular beam epitaxy (MBE), of CdTe on Si and GaAs substrates. The effect of temperature changes on wafer curvature throughout the growth sequence is documented using a multi-beam optical sensor developed by K-Space Associates. This monitoring technique makes possible the study of growth sequences which employ annealing schemes and/or interlayers to influence the final residual stress state of the heteroepitaxial structures.

  1. Atomic-force microscopy and photoluminescence of nanostructured CdTe

    SciTech Connect

    Babentsov, V.; Sizov, F.; Franc, J.; Luchenko, A.; Svezhentsova, E. Tsybrii, Z.

    2013-09-15

    Low-dimensional CdTe nanorods with a diameter of 10-30 nm and a high aspect ratio that reaches 100 are studied. The nanorods are grown by the physical vapor transport method with the use of Bi precipitates on the substrates. In addition, thin films of closely packed CdTe nanorods with the transverse dimensions {approx}(100-200) nm are grown. Atomic-force microscopy shows that the cross sections of all of the nanorods were hexagonally shaped. By photoluminescence measurements, the inference about the wurtzite structure of CdTe is supported, and the structural quality, electron-phonon coupling, and defects are analyzed. On the basis of recent ab initio calculations, the nature of defects responsible for the formation of deep levels in the CdTe layers and bulk crystals are analyzed.

  2. First-Principles Study of Back Contact Effects on CdTe Thin Film Solar Cells

    SciTech Connect

    Du, Mao-Hua

    2009-01-01

    Forming a chemically stable low-resistance back contact for CdTe thin-film solar cells is critically important to the cell performance. This paper reports theoretical study of the effects of the back-contact material, Sb{sub 2}Te{sub 3}, on the performance of the CdTe solar cells. First-principles calculations show that Sb impurities in p-type CdTe are donors and can diffuse with low diffusion barrier. There properties are clearly detrimental to the solar-cell performance. The Sb segregation into the grain boundaries may be required to explain the good efficiencies for the CdTe solar cells with Sb{sub 2}Te{sub 3} back contacts.

  3. Characterization of CdTe Nanoparticles Fabricated by Pulsed Electron Deposition Technique at Different Ablation Parameters

    SciTech Connect

    Jackson, E.; Aga, R. Jr.; Steigerwald, A.; Ueda, A.; Pan, Z.; Collins, W. E.; Mu, R.

    2008-03-13

    Telluride (CdTe) is a front-runner photovoltaic (PV) material because it has already attained efficiencies above 16%. The fabrication of CdTe nanoparticles has aroused considerable interest because of their potential application as active layer in organic/inorganic hybrid solar cells. They can also be used for sensitisation of wide band gap semiconductors. In this work, we explore pulsed electron beam deposition (PED) technique to fabricate CdTe nanoparticles. Two ablation parameters, namely background gas pressure and electron energy were varied to investigate their effects on the nanoparticle formation. AFM and optical transmission measurements indicate that we have fabricated CdTe nanocrystalline films exhibiting quantum confinement effect. These films contain scattered nanoparticles with diameters varying from 40 nm to 500 nm, which contribute to the optical absorption near the bulk bandgap energy. However, increasing the background pressure to 19 mTorr improves the nanocrystalline film uniformity.

  4. APT mass spectrometry and SEM data for CdTe solar cells

    DOE PAGES

    Li, Chen; Paudel, Naba R.; Yan, Yanfa; Pennycook, Stephen J.; Poplawsky, Jonathan D.; Guo, Wei

    2016-03-16

    Atom probe tomography (APT) data acquired from a CAMECA LEAP 4000 XHR for the CdS/CdTe interface for a non-CdCl2 treated CdTe solar cell as well as the mass spectrum of an APT data set including a GB in a CdCl2-treated CdTe solar cell are presented. Scanning electron microscopy (SEM) data showing the evolution of sample preparation for APT and scanning transmission electron microscopy (STEM) electron beam induced current (EBIC) are also presented. As a result, these data show mass spectrometry peak decomposition of Cu and Te within an APT dataset, the CdS/CdTe interface of an untreated CdTe solar cell, preparationmore » of APT needles from the CdS/CdTe interface in superstrate grown CdTe solar cells, and the preparation of a cross-sectional STEM EBIC sample.« less

  5. Growth and fabrication method of CdTe and its performance as a radiation detector

    NASA Astrophysics Data System (ADS)

    Park, Soojeong; Kim, Hyojin; Kim, Dojin

    2015-01-01

    We report the nitrogen-monoxide (NO) gas-sensing properties of transparent p-type copper-oxide (CuO) nanorod arrays synthesized by using the hydrothermal method with a CuO nanoparticle seed layer deposited on a glass substrate via sputtering process. We synthesized polycrystalline CuO nanorods measuring 200 to 300 nm in length and 20 to 30 nm in diameter for three controlled molarity ratios of 1:1, 1:2 and 1:4 between copper nitrate trihydrate [Cu(NO2)2·3H2O] and hexamethylenetetramine (C6H12N4). The crystal structures and morphologies of the synthesized CuO nanorod arrays were examined using grazing incidence X-ray diffraction and scanning electron microscopy. The gas-sensing measurements for NO gas in dry air indicated that the CuO nanorodarray-based gas sensors synthesized under hydrothermal condition at a molarity ratio of 1:2 showed the best gas sensing response to NO gas. These CuO nanorod-array gas sensors exhibited a highly sensitive response to NO gas, with a maximum sensitivity of about 650% for 10 ppm NO in dry air at an operating temperature of 100 ℃. These transparent p-type CuO nanorod-array gas sensors have shown a reversible and reliable response to NO gas over a range of operating temperatures. These results indicate certain potential use of p-type oxide semiconductor CuO nanorods as sensing materials for several types of gas sensors, including p — n junction gas sensors.

  6. MS Detectors

    SciTech Connect

    Koppenaal, David W.; Barinaga, Charles J.; Denton, M Bonner B.; Sperline, Roger P.; Hieftje, Gary M.; Schilling, G. D.; Andrade, Francisco J.; Barnes IV., James H.

    2005-11-01

    Good eyesight is often taken for granted, a situation that everyone appreciates once vision begins to fade with age. New eyeglasses or contact lenses are traditional ways to improve vision, but recent new technology, i.e. LASIK laser eye surgery, provides a new and exciting means for marked vision restoration and improvement. In mass spectrometry, detectors are the 'eyes' of the MS instrument. These 'eyes' have also been taken for granted. New detectors and new technologies are likewise needed to correct, improve, and extend ion detection and hence, our 'chemical vision'. The purpose of this report is to review and assess current MS detector technology and to provide a glimpse towards future detector technologies. It is hoped that the report will also serve to motivate interest, prompt ideas, and inspire new visions for ion detection research.

  7. Study of Cu-related Defect States in Single-crystal CdTe

    NASA Astrophysics Data System (ADS)

    Corwine, Caroline; Sites, James; Gessert, Timothy; Metzger, Wyatt; Dippo, Pat; Duda, Anna

    2003-10-01

    We have studied single-crystal CdTe using low-temperature photoluminescence (PL) in an effort to understand the effects of copper on the deep levels, as well as the effect of a bromine methanol (BrMe) etch on subsequent copper diffusion into CdTe. In present polycrystalline CdS/CdTe solar cell technology, the use of a back contact that contains Cu is necessary to produce high-efficiency cells. However, it is not generally understood why Cu is necessary for these devices to function well. In order to obtain further advances in the efficiencies of these solar cells, it is important to know how the back contact process may affect the defect states in CdTe. PL is one tool used to study defect states. However, before PL can be used effectively for polycrystalline CdTe solar cells, relevant spectral features first must be interpreted for single-crystal CdTe. All PL in this study was taken at 4.5 K. We report on PL peaks at 1.40 and 1.45 eV, which are seen only after Cu is diffused into single-crystal CdTe.

  8. Facile synthesis of straight and branched CdTe nanowires using CdO as precursor.

    PubMed

    Liu, Sheng; Yang, Chunyan; Zhang, Wen-Hua; Li, Can

    2011-12-01

    High-quality colloidal CdTe nanowires (NWs) containing both straight and branched ones were controllably prepared via a solution-based approach, using a low melting Bi nanoparticles as catalysts, CdO and tributylphosphine telluride (TBP-Te) as precursors, and a tri-n-octylphosphine oxide/tri-n-octylphosphine (TOPO/TOP) mixture as solvent. The resulting straight CdTe NWs have typical diameters below 20 nm accompanying with lengths exceeding 10 microm. In the case of branched CdTe NWs, tripod, V-shaped and y-shaped morphologies are obtained by decreasing the apparent Cd/Te molar ratio. It is found that, as the surface capping ligands, di-n-octylphosphinic acid (DOPA) is superior to decylphosphonic acid (DPA) in the reproducible growth of high-quality CdTe NWs. Since highly toxic dimethylcadmium, a cadmium precursor widely used in literatures, is replaced by CdO and the amount of the TOPO/TOP solvent mixture is significantly reduced, a relative safe and economical synthetic approach of high-quality colloidal CdTe NWs with controllable morphology is thus presented.

  9. In situ oxygen incorporation and related issues in CdTe /CdS photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Emziane, M.; Durose, K.; Halliday, D. P.; Bosio, A.; Romeo, N.

    2006-07-01

    CdTe /CdS/SnO2/ITO:F solar cell devices were investigated using quantitative secondary ion mass spectrometry (SIMS) depth profiling. They were grown on sapphire substrates and potentially active impurity species were analyzed. The SIMS data were calibrated for both CdS window layer (grown by sputtering) and CdTe absorber layer (deposited by close-space sublimation). For comparison, some of the samples were grown with and without oxygen incorporation into the CdTe layer during its deposition, and with and without postgrowth cadmium chloride (CdCl2) annealing in air and chemical etching. These devices were back contacted using Mo /Sb2Te3 sputtered layers. It was shown that for CdTe and CdS layers there was a correlation between the concentrations of oxygen and chlorine. In situ oxygen incorporation in the CdTe layer yielded a substantial improvement in the device parameters and achieved an efficiency of 14% compared to 11.5% for devices fabricated in the same conditions without oxygen incorporation in CdTe. In light of our previous reports, this study also led to a clear determination of the origin of Na and Si traces found in these devices.

  10. Oxygen Incorporation During Fabrication of Substrate CdTe Photovoltaic Devices: Preprint

    SciTech Connect

    Duenow, J. N.; Dhere, R. G.; Kuciauskas, D.; Li, J. V.; Pankow, J. W.; DeHart, C. M.; Gessert, T. A.

    2012-06-01

    Recently, CdTe photovoltaic (PV) devices fabricated in the nonstandard substrate configuration have attracted increasing interest because of their potential compatibility with flexible substrates such as metal foils and polymer films. This compatibility could lead to the suitability of CdTe for roll-to-roll processing and building-integrated PV. Currently, however, the efficiencies of substrate CdTe devices reported in the literature are significantly lower ({approx}6%-8%) than those of high-performance superstrate devices ({approx}17%) because of significantly lower open-circuit voltage (Voc) and fill factor (FF). In our recent device development efforts, we have found that processing parameters required to fabricate high-efficiency substrate CdTe PV devices differ from those necessary for traditional superstrate CdTe devices. Here, we investigate how oxygen incorporation in the CdTe deposition, CdCl2 heat treatment, CdS deposition, and post-deposition heat treatment affect device characteristics through their effects on the junction. By adjusting whether oxygen is incorporated during these processing steps, we have achieved Voc values greater than 860 mV and efficiencies greater than 10%.

  11. Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole.

    PubMed

    Li, Qin; Tan, Xuanping; Li, Jin; Pan, Li; Liu, Xiaorong

    2015-04-15

    Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42 ng mL(-1) (3.4 ng mL(-1)) and the quantitative determination range was 0-2.8 μg mL(-1) with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results.

  12. Glutathione-capped CdTe nanocrystals as probe for the determination of fenbendazole

    NASA Astrophysics Data System (ADS)

    Li, Qin; Tan, Xuanping; Li, Jin; Pan, Li; Liu, Xiaorong

    2015-04-01

    Water-soluble glutathione (GSH)-capped CdTe quantum dots (QDs) were synthesized. In pH 7.1 PBS buffer solution, the interaction between GSH-capped CdTe QDs and fenbendazole (FBZ) was investigated by spectroscopic methods, including fluorescence spectroscopy, ultraviolet-visible absorption spectroscopy, and resonance Rayleigh scattering (RRS) spectroscopy. In GSH-capped CdTe QDs solution, the addition of FBZ results in the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs. And the quenching intensity (enhanced RRS intensity) was proportional to the concentration of FBZ in a certain range. Investigation of the interaction mechanism, proved that the fluorescence quenching and RRS enhancement of GSH-capped CdTe QDs by FBZ is the result of electrostatic attraction. Based on the quenching of fluorescence (enhancement of RRS) of GSH-capped CdTe QDs by FBZ, a novel, simple, rapid and specific method for FBZ determination was proposed. The detection limit for FBZ was 42 ng mL-1 (3.4 ng mL-1) and the quantitative determination range was 0-2.8 μg mL-1 with a correlation of 0.9985 (0.9979). The method has been applied to detect FBZ in real simples and with satisfactory results.

  13. CdTe quantum dots as a novel biosensor for Serratia marcescens and Lipopolysaccharide.

    PubMed

    Ebrahim, Sh; Reda, M; Hussien, A; Zayed, D

    2015-01-01

    The main objective of this work is to synthesize CdTe quantum dots (QDs) conjugated with Concanavalin A (Con A) as a novel biosensor to be selective and specific for the detection of Lipopolysaccharide (LPS). In addition, the conjugated CdTe QDs-Con A was used as fluorescence labels to capture Serratia marcescens bacteria through the recognition between CdTe QDs-Con A and LPS of S. marcescens. The appearance of the lattice plans in the high resolution transmission electron photograph indicated a high crystalline with an average size of 4-5 nm for the CdTe QDs. The results showed that the relative fluorescence intensity of CdTe QDs-Con A decreased linearly with LPS concentration in the range from 10 to 90 fg/mL and with correlation coefficient (R(2)) equal to 0.9713. LPS surrounding the S. marcescens bacteria was bound to the CdTe QDs-Con A and leads to quenching of PL intensity. It was found that a good linear relationship between the relative PL intensity and the logarithmic of cell population of S. marcescens in range from 1×10 to 1×10(6) CFU/mL at pH 7 with R(2) of 0.952 was established.

  14. Properties of RF sputtered cadmium telluride (CdTe) thin films: Influence of deposition pressure

    NASA Astrophysics Data System (ADS)

    Kulkarni, R. R.; Pawbake, A. S.; Waykar, R. G.; Rondiya, S. R.; Jadhavar, A. A.; Pandharkar, S. M.; Karpe, S. D.; Diwate, K. D.; Jadkar, S. R.

    2016-04-01

    Influence of deposition pressure on structural, morphology, electrical and optical properties of CdTe thin films deposited at low substrate temperature (100°C) by RF magnetron sputtering was investigated. The formation of CdTe was confirmed by low angle XRD and Raman spectroscopy. The low angle XRD analysis revealed that the CdTe films have zinc blende (cubic) structure with crystallites having preferred orientation in (111) direction. Raman spectra show the longitudinal optical (LO) phonon mode peak ˜ 165.4 cm-1 suggesting high quality CdTe film were obtained over the entire range of deposition pressure studied. Scanning electron microscopy analysis showed that films are smooth, homogenous, and crack-free with no evidence of voids. The EDAX data revealed that CdTe films deposited at low deposition pressure are high-quality stoichiometric. However, for all deposition pressures, films are rich in Cd relative to Te. The UV-Visible spectroscopy analysis show the blue shift in absorption edge with increasing the deposition pressure while the band gap show decreasing trend. The highest electrical conductivity was obtained for the film deposited at deposition pressure 1 Pa which indicates that the optimized deposition pressure for our sputtering unit is 1 Pa. Based on the experimental results, these CdTe films can be useful for the application in the flexible solar cells and other opto-electronic devices.

  15. Epitaxial Growth of CdTe by H2 Sputtering

    NASA Astrophysics Data System (ADS)

    Nishibayashi, Yoshiki; Tokumitsu, Yoji; Saito, Koji; Imura, Takeshi; Osaka, Yukio

    1988-10-01

    CdTe films can be grown epitaxially on InSb(100) by chemical sputtering in H2. The crystalline quality of the epitaxial layers is improved when the substrate temperatures are in the range of 200 to 250°C at a high rf discharge power of 400 W. In channeling experiments employing Rutherford backscattering spectrometry, the χmin (aligned yield/random yield) in the film prepared at 270°C and 400 W is 9.5%. A lattice strain of 0.05% is obtained from the results of X-ray diffraction. These values show that the crystalline quality of the epitaxial film grown by H2 sputtering is superior to the film grown by Ar sputtering.

  16. Theoretical study of intrinsic defects in CdTe

    NASA Astrophysics Data System (ADS)

    Menéndez-Proupin, E.; Orellana, W.

    2016-05-01

    The quantum states and thermodynamical properties of the Cd and Te vacancies in CdTe are studied by first principles calculations. It is shown that the band structure of a cubic 64-atoms supercell with a Te vacancy is dramatically different from the band structure of the perfect crystal, suggesting that it cannot be used as model to calculate isolated defects. This flaw is solved modeling the Te vacancy within a cubic 216-atoms supercell. However, even with this large supercell, the 2— charge state relaxes to an incorrect distorted structure. This distortion is driven by partial filling of the conduction band induced by the k-point sampling. The correct structures and formation energies are obtained by relaxation with restriction of system symmetry, followed by band-filling correction to the energy, or by using a larger supercell that allows sampling the Brillouin zone with a single k-point.

  17. Photon detectors

    SciTech Connect

    Va`vra, J.

    1995-10-01

    J. Seguinot and T. Ypsilantis have recently described the theory and history of Ring Imaging Cherenkov (RICH) detectors. In this paper, I will expand on these excellent review papers, by covering the various photon detector designs in greater detail, and by including discussion of mistakes made, and detector problems encountered, along the way. Photon detectors are among the most difficult devices used in physics experiments, because they must achieve high efficiency for photon transport and for the detection of single photo-electrons. For gaseous devices, this requires the correct choice of gas gain in order to prevent breakdown and wire aging, together with the use of low noise electronics having the maximum possible amplification. In addition, the detector must be constructed of materials which resist corrosion due to photosensitive materials such as, the detector enclosure must be tightly sealed in order to prevent oxygen leaks, etc. The most critical step is the selection of the photocathode material. Typically, a choice must be made between a solid (CsI) or gaseous photocathode (TMAE, TEA). A conservative approach favors a gaseous photocathode, since it is continuously being replaced by flushing, and permits the photon detectors to be easily serviced (the air sensitive photocathode can be removed at any time). In addition, it can be argued that we now know how to handle TMAE, which, as is generally accepted, is the best photocathode material available as far as quantum efficiency is concerned. However, it is a very fragile molecule, and therefore its use may result in relatively fast wire aging. A possible alternative is TEA, which, in the early days, was rejected because it requires expensive CaF{sub 2} windows, which could be contaminated easily in the region of 8.3 eV and thus lose their UV transmission.

  18. Pyroelectric detectors

    NASA Technical Reports Server (NTRS)

    Haller, Eugene E.; Beeman, Jeffrey; Hansen, William L.; Hubbard, G. Scott; Mcmurray, Robert E., Jr.

    1990-01-01

    The multi-agency, long-term Global Change programs, and specifically NASA's Earth Observing system, will require some new and advanced photon detector technology which must be specifically tailored for long-term stability, broad spectral range, cooling constraints, and other parameters. Whereas MCT and GaAs alloy based photovoltaic detectors and detector arrays reach most impressive results to wavelengths as long as 12 microns when cooled to below 70 K, other materials, such as ferroelectrics and pyroelectrics, appear to offer special opportunities beyond 12 microns and above 70 K. These materials have found very broad use in a wide variety of room temperature applications. Little is known about these classes of materials at sub-room temperatures and no photon detector results have been reported. From the limited information available, researchers conclude that the room temperature values of D asterisk greater than or equal to 10(exp 9) cm Hz(exp 1/2)/W may be improved by one to two orders of magnitude upon cooling to temperatures around 70 K. Improvements of up to one order of magnitude appear feasible for temperatures achievable by passive cooling. The flat detector response over a wavelength range reaching from the visible to beyond 50 microns, which is an intrinsic advantage of bolometric devices, makes for easy calibration. The fact that these materials have been developed for reduced temperature applications makes ferro- and pyroelectric materials most attractive candidates for serious exploration.

  19. PHASE DETECTOR

    DOEpatents

    Kippenhan, D.O.

    1959-09-01

    A phase detector circuit is described for use at very high frequencies of the order of 50 megacycles. The detector circuit includes a pair of rectifiers inverted relative to each other. One voltage to be compared is applied to the two rectifiers in phase opposition and the other voltage to be compared is commonly applied to the two rectifiers. The two result:ng d-c voltages derived from the rectifiers are combined in phase opposition to produce a single d-c voltage having amplitude and polarity characteristics dependent upon the phase relation between the signals to be compared. Principal novelty resides in the employment of a half-wave transmission line to derive the phase opposing signals from the first voltage to be compared for application to the two rectifiers in place of the transformer commonly utilized for such purpose in phase detector circuits for operation at lower frequency.

  20. High-Resolution Compton-Suppressed CZT Detector for Fission Products Identification

    SciTech Connect

    R. Aryaeinejd; J. K. Hartwell; Wade W. Scates

    2004-10-01

    Room temperature semiconductor CdZnTe (CZT) detectors are currently limited to total detector volumes of 1-2 cm3, which is dictated by the poor charge transport characteristics. Because of this size limitation one of the problems in accurately determining isotope identification is the enormous background from the Compton scattering events. Eliminating this background will not only increase the sensitivity and accuracy of measurements but also help us to resolve peaks buried under the background and peaks in close vicinity of others. We are currently developing a fission products detection system based on the Compton-suppressed CZT detector. In this application, the detection system is required to operate in high radiation fields. Therefore, a small 10x10x5 mm3 CZT detector is placed inside the center of a well-shielded 3" in diameter by 3" long Nal detector. So far we have been able to successfully reduce the Compton background by a factor of 5.4 for a 137Cs spectrum. This reduction of background will definitely enhance the quality of the gamma-ray spectrum in the information-rich energy range below 1 MeV, which consequently increases the detection sensitivity. In this work, we will discuss the performance of this detection system as well as its applications.

  1. Hydrogen detector

    DOEpatents

    Kanegae, Naomichi; Ikemoto, Ichiro

    1980-01-01

    A hydrogen detector of the type in which the interior of the detector is partitioned by a metal membrane into a fluid section and a vacuum section. Two units of the metal membrane are provided and vacuum pipes are provided independently in connection to the respective units of the metal membrane. One of the vacuum pipes is connected to a vacuum gauge for static equilibrium operation while the other vacuum pipe is connected to an ion pump or a set of an ion pump and a vacuum gauge both designed for dynamic equilibrium operation.

  2. Microwave detector

    DOEpatents

    Meldner, Heiner W.; Cusson, Ronald Y.; Johnson, Ray M.

    1986-01-01

    A microwave detector (10) is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite (26, 28) produces a magnetization field flux that links a B-dot loop (16, 20). The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means (18, 22) are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.

  3. Microwave detector

    DOEpatents

    Meldner, H.W.; Cusson, R.Y.; Johnson, R.M.

    1985-02-08

    A microwave detector is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite produces a magnetization field flux that links a B-dot loop. The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.

  4. Silicon Detectors

    NASA Astrophysics Data System (ADS)

    Sadrozinski, Hartmut

    2014-03-01

    The use of silicon detectors has experienced an exponential growth in accelerator and space based experiments, similar to trends in the semiconductor industry as a whole, usually paraphrased as ``Moore's Law.'' Some of the essentials for this phenomenon will be presented, together with examples of the exciting science results which it enabled. With the establishment of a ``semiconductor culture'' in universities and laboratories around the world, an increased understanding of the sensors results in thinner, faster, more radiation-resistant detectors, spawning an amazing wealth of new technologies and applications, which will be the main subject of the presentation.

  5. Microwave detector

    SciTech Connect

    Meldner, H.W.; Cusson, R.Y.; Johnson, R.M.

    1986-12-02

    A detector is described for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations, the detector comprising: a B-dot loop linking the magnetic field of the microwave pulse; a biased ferrite, that produces a magnetization field flux that links the B-dot loop. The ferrite is positioned within the B-dot loop so that the magnetic field of the microwave pulse interacts with the ferrite and thereby participates in the formation of the magnetization field flux; and high-frequency insensitive means for measuring electric voltage or current induced in the B-dot loop.

  6. FOXSI: Properties of optics and detectors for hard-X rays

    NASA Astrophysics Data System (ADS)

    Camilo Buitrago-Casas, Juan; Glesener, Lindsay; Christe, Steven; Krucker, Sam; Ishikawa, Shin-nosuke; Foster, Natalie

    2015-04-01

    The Focusing Optics X-ray Solar Imager (FOXSI) is a state-of-the-art direct focusing X-ray telescope designed to observe the Sun. This experiment completed its second flight onboard a sounding rocket last December 11, 2014 from the White Sands Missile Range in New Mexico. The optics use a set of iridium-coated nickel/cobalt mirrors made using a replication technique based on an electroformed perfect polished surface. Since this technique creates full shells that no need to be co-aligned with other segments, an angular resolution of up to ~5 arcsec is gotten. The FOXSI focal plane consists of seven double-sided strip detectors. Five Silicon and 2 CdTe detectors were used during the second flight.We present on various properties of Wolter-I optics that are applicable to solar HXR observation, including ray-tracing simulations of the single-bounce (“ghost ray”) patterns from sources outside the field of view and angular resolution for different source angles and effective area measurements of the FOXSI optics. We also present the detectors calibration results, paying attention to energy resolution (~0.5 keV), energy thresholds (~4-15 keV for Silicon and ~4-20 keV for CdTe detectors), and spatial coherence of these values over the entire detector.

  7. van der Waals epitaxy of CdTe thin film on graphene

    NASA Astrophysics Data System (ADS)

    Mohanty, Dibyajyoti; Xie, Weiyu; Wang, Yiping; Lu, Zonghuan; Shi, Jian; Zhang, Shengbai; Wang, Gwo-Ching; Lu, Toh-Ming; Bhat, Ishwara B.

    2016-10-01

    van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

  8. PIXSCAN: Pixel detector CT-scanner for small animal imaging

    NASA Astrophysics Data System (ADS)

    Delpierre, P.; Debarbieux, F.; Basolo, S.; Berar, J. F.; Bonissent, A.; Boudet, N.; Breugnon, P.; Caillot, B.; Cassol Brunner, F.; Chantepie, B.; Clemens, J. C.; Dinkespiler, B.; Khouri, R.; Koudobine, I.; Mararazzo, V.; Meessen, C.; Menouni, M.; Morel, C.; Mouget, C.; Pangaud, P.; Peyrin, F.; Rougon, G.; Sappey-Marinier, D.; Valton, S.; Vigeolas, E.

    2007-02-01

    The PIXSCAN is a small animal CT-scanner based on hybrid pixel detectors. These detectors provide very large dynamic range of photons counting at very low detector noise. They also provide high counting rates with fast image readout. Detection efficiency can be optimized by selecting the sensor medium according to the working energy range. Indeed, the use of CdTe allows a detection efficiency of 100% up to 50 keV. Altogether these characteristics are expected to improve the contrast of the CT-scanner, especially for soft tissues, and to reduce both the scan duration and the absorbed dose. A proof of principle has been performed by assembling into a PIXSCAN-XPAD2 prototype the photon counting pixel detector initially built for detection of X-ray synchrotron radiations. Despite the relatively large pixel size of this detector (330×330 μm 2), we can present three-dimensional tomographic reconstruction of mice at good contrast and spatial resolution. A new photon counting chip (XPAD3) is designed in sub-micronique technology to achieve 130×130 μm 2 pixels. This improved circuit has been equipped with an energy selection circuit to act as a band-pass emission filter. Furthermore, the PIXSCAN-XPAD3 hybrid pixel detectors will be combined with the Lausanne ClearPET scanner demonstrator. CT image reconstruction in this non-conventional geometry is under study for this purpose.

  9. Vertex detectors

    SciTech Connect

    Lueth, V.

    1992-07-01

    The purpose of a vertex detector is to measure position and angles of charged particle tracks to sufficient precision so as to be able to separate tracks originating from decay vertices from those produced at the interaction vertex. Such measurements are interesting because they permit the detection of weakly decaying particles with lifetimes down to 10{sup {minus}13} s, among them the {tau} lepton and charm and beauty hadrons. These two lectures are intended to introduce the reader to the different techniques for the detection of secondary vertices that have been developed over the past decades. The first lecture includes a brief introduction to the methods used to detect secondary vertices and to estimate particle lifetimes. It describes the traditional technologies, based on photographic recording in emulsions and on film of bubble chambers, and introduces fast electronic registration of signals derived from scintillating fibers, drift chambers and gaseous micro-strip chambers. The second lecture is devoted to solid state detectors. It begins with a brief introduction into semiconductor devices, and then describes the application of large arrays of strip and pixel diodes for charged particle tracking. These lectures can only serve as an introduction the topic of vertex detectors. Time and space do not allow for an in-depth coverage of many of the interesting aspects of vertex detector design and operation.

  10. Monte Carlo Simulations of Background Spectra in Integral Imager Detectors

    NASA Technical Reports Server (NTRS)

    Armstrong, T. W.; Colborn, B. L.; Dietz, K. L.; Ramsey, B. D.; Weisskopf, M. C.

    1998-01-01

    Predictions of the expected gamma-ray backgrounds in the ISGRI (CdTe) and PiCsIT (Csl) detectors on INTEGRAL due to cosmic-ray interactions and the diffuse gamma-ray background have been made using a coupled set of Monte Carlo radiation transport codes (HETC, FLUKA, EGS4, and MORSE) and a detailed, 3-D mass model of the spacecraft and detector assemblies. The simulations include both the prompt background component from induced hadronic and electromagnetic cascades and the delayed component due to emissions from induced radioactivity. Background spectra have been obtained with and without the use of active (BGO) shielding and charged particle rejection to evaluate the effectiveness of anticoincidence counting on background rejection.

  11. The evolution of scintillating medical detectors

    NASA Astrophysics Data System (ADS)

    Hell, E.; Knüpfer, W.; Mattern, D.

    2000-11-01

    The principle of scintillation detectors has been among the first realizations of radiation detectors. Despite ongoing attempts to switch to direct converting detectors, scintillators have shown great persistence in the field of medical imaging. In radiography, computer tomography and nuclear medicine, a variety of scintillating devices are the 'workhorses' of the clinician today. For radiography, flat X-ray detectors (FDs) with evaporated scintillation layers are at the level of product introduction. However, X-ray image intensifier tubes (XIIs) are competitive and still have features that will be hard to beat in the near future. Although XIIs have disadvantages, they have experienced a significant evolution in robust image quality and cost reduction over the decades. The so-called 'offline' detectors from film to storage phosphors seemed to have reached a plateau since the late 1970s. However, the distinction between on- and offline may soften in the future, because of new readout concepts. Detectors in computer tomography (CT) have evolved from scintillators to gaseous direct converters back to scintillators. Extreme timing requirements and detector modularity have ruled out designs that would rank as `high performance' in other fields. Modern ultra-fast ceramic scintillation detectors are a prerequisite of subsecond CT and leave breathing room for future scan times even below 0.5 s. The field of nuclear medicine is a good example of how difficult it is, to replace a cheap and reliable technology. Since many years, direct converters like CdTe and the likes are discussed to overthrow the regime of NaI:Tl in combination with photomultipliers (PMTs). Both components are well known since the 1950s and have shown remarkable staying power. Still the scintillator with the highest light output, NaI:Tl in combination with the basically noiseless PMT is almost unbeatable in low cost. In combination with modern digital electronics, drawbacks of analog circuitry like

  12. Caractérisation temporelle et spectrale de la photoluminescence de boîtes quantiques de CdZnTe

    NASA Astrophysics Data System (ADS)

    Brimont, C.; Cronenberger, S.; Crégut, O.; Gallart, M.; Hönerlage, B.; Gilliot, P.

    2006-10-01

    Nous étudions la relaxation des paires électron-trou dans des échantillons de boîtes quantiques auto-assemblées de CdZnTe riches en cadmium incluses dans un puits quantique riche en zinc. Dans ce type de système, le couplage électron-phonon LO est le principal mécanisme responsable de la relaxation d'énergie des porteurs. Nous mesurons cette relaxation par photoluminescence résolue en temps, en fonction de l'intensité et de l'énergie de photon de l'excitation.

  13. Photodegradation of Mercaptopropionic Acid- and Thioglycollic Acid-Capped CdTe Quantum Dots in Buffer Solutions.

    PubMed

    Miao, Yanping; Yang, Ping; Zhao, Jie; Du, Yingying; He, Haiyan; Liu, Yunshi

    2015-06-01

    CdTe quantum dots (QDs) were synthesized by 3-mercaptopropionic acid (MPA) and thioglycollic acid (TGA) as capping agents. It is confirmed that TGA and MPA molecules were attached on the surface of the QDs using Fourier transform infrared (FT-IR) spectra. The movement of the QDs in agarose gel electrophoresis indicated that MPA-capped CdTe QDs had small hydrodynamic diameter. The photoluminescence (PL) intensity of TGA-capped QDs is higher than that of MPA-capped QDs at same QD concentration because of the surface passivation of TGA. To systemically investigate the photodegradation, CdTe QDs with various PL peak wavelengths were dispersed in phosphate buffered saline (PBS) and Tris-borate-ethylenediaminetetraacetic acid (TBE) buffer solutions. It was found that the PL intensity of the QDs in PBS decreased with time. The PL peak wavelengths of the QDs in PBS solutions remained unchanged. As for TGA-capped CdTe QDs, the results of PL peak wavelengths in TBE buffer solutions indicated that S(2-) released by TGA attached to Cd(2+) and formed CdS-like clusters layer on the surface of aqueous CdTe QDs. In addition, the number of TGA on the CdTe QDs surface was more than that of MPA. When the QDs were added to buffer solutions, agents were removed from the surface of CdTe QDs, which decreased the passivation of agents thus resulted in photodegradation of CdTe QDs in buffer solutions.

  14. {CdTe(111) B}/{Si(100) } structure grown by metalorganic vapor phase epitaxy with Te adsorption and annealing

    NASA Astrophysics Data System (ADS)

    Nishino, Hironori; Nishijima, Yoshito

    1996-10-01

    We studied the crystal structure of CdTe(111)B layers directly grown on Si(100) by MOVPE using a new pre-growth process, which includes a metalorganic Te adsorption and an annealing process. In this paper, we discussed the CdTe structure from the three aspects of antiphase, twinning and tilt. We investigated the dependence of the antiphase content in CdTe(111)B on the anneal temperature and the Si misorientation angle. From the results, we assume that the origin of the antiphase formation is the difference in the arrangement of adsorbed Te atoms. Te arrangement leading to antiphase formation occurs on Si terraces away from steps at relatively low temperatures. We reduced most of the twinning in epilayers by optimizing the {VI}/{II} ratio. We think the remaining twinning was confined to near the interface and it nucleated from the Te arrangement on terraces. We found that the Si(100)-CdTe(111) tilt was much smaller than that expected from the well-known Nagai model. We propose that a negative tilt is induced to reduce the lateral mismatch. To adjust the lateral distance of unit cells, 30 CdTe lattices match to 31 Si lattices. CdTe(111)B planes are inclined to reduce the remaining mismatch between two lattices. This initial tilt also causes wider CdTe terraces. We modified Nagai's tilting model for this reconstructed CdTe surface. The total tilt angle is defined by these two tilting mechanisms.

  15. Emitter/absorber interface of CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Song, Tao; Kanevce, Ana; Sites, James R.

    2016-06-01

    The performance of CdTe solar cells can be very sensitive to the emitter/absorber interface, especially for high-efficiency cells with high bulk lifetime. Performance losses from acceptor-type interface defects can be significant when interface defect states are located near mid-gap energies. Numerical simulations show that the emitter/absorber band alignment, the emitter doping and thickness, and the defect properties of the interface (i.e., defect density, defect type, and defect energy) can all play significant roles in the interface recombination. In particular, a type I heterojunction with small conduction-band offset (0.1 eV ≤ ΔEC ≤ 0.3 eV) can help maintain good cell efficiency in spite of high interface defect density, much like with Cu(In,Ga)Se2 (CIGS) cells. The basic principle is that positive ΔEC, often referred to as a "spike," creates an absorber inversion and hence a large hole barrier adjacent to the interface. As a result, the electron-hole recombination is suppressed due to an insufficient hole supply at the interface. A large spike (ΔEC ≥ 0.4 eV), however, can impede electron transport and lead to a reduction of photocurrent and fill-factor. In contrast to the spike, a "cliff" (ΔEC < 0 eV) allows high hole concentration in the vicinity of the interface, which will assist interface recombination and result in a reduced open-circuit voltage. Another way to mitigate performance losses due to interface defects is to use a thin and highly doped emitter, which can invert the absorber and form a large hole barrier at the interface. CdS is the most common emitter material used in CdTe solar cells, but the CdS/CdTe interface is in the cliff category and is not favorable from the band-offset perspective. The ΔEC of other n-type emitter choices, such as (Mg,Zn)O, Cd(S,O), or (Cd,Mg)Te, can be tuned by varying the elemental ratio for an optimal positive value of ΔEC. These materials are predicted to yield higher voltages and would therefore be

  16. Optical and electrical properties of hydrothermally prepared CdTe nanowires

    NASA Astrophysics Data System (ADS)

    Hadia, N. M. A.; Awad, M. A.; Mohamed, S. H.; Ibrahim, E. M. M.

    2016-10-01

    The hydrothermal process was used to synthesize CdTe nanowires (NWs). Various analytical techniques were used to characterize the obtained NWs. The wire diameters were in the range 35-60 nm, and the lengths were >5 μm. The CdTe NWs had zinc-blende crystal structure. The NWs had high uniformity and high yield. FTIR analysis revealed the presence of the characteristic vibrational spectra of oxygen and hydrogen bounded to Cd and Te in CdTe NWs. The optical band gap value was 2.09 eV. The CdTe NWs showed a strong red emission band centered around 620.3 nm. The conductivity measurements were carried out in the temperature range 300-500 K and in air atmosphere. Two types of conduction mechanisms were observed with activation energies of 0.27 and 0.17 eV at high and low temperature regions, respectively. These results validate the potential of CdTe NWs for optoelectronic applications.

  17. BSA activated CdTe quantum dot nanosensor for antimony ion detection.

    PubMed

    Ge, Shenguang; Zhang, Congcong; Zhu, Yuanna; Yu, Jinghua; Zhang, Shuangshuang

    2010-01-01

    A novel fluorescent nanosensor for Sb(3+) determination was reported based on thioglycolic acid (TGA)-capped CdTe quantum dot (QD) nanoparticles. It was the first antimony ion sensor using QD nanoparticles in a receptor-fluorophore system. The water-soluable TGA-capped CdTe QDs were prepared through a hydrothermal route, NaHTe was used as the Te precursor for CdTe QDs synthesis. Bovine serum albumin (BSA) conjugated to TGA-capped CdTe via an amide link interacting with carboxyl of the TGA-capped CdTe. When antimony ion enters the BSA, the lone pair electrons of the nitrogen and oxygen atom become involved in the coordination, switching off the QD emission and a dramatic quenching of the fluorescence intensity results, allowing the detection of low concentrations of antimony ions. Using the operating principle, the antimony ion sensor based on QD nanoparticles showed a very good linearity in the range 0.10-22.0 microg L(-1), with the detection limit lower than 2.94 x 10(-8) g L(-1) and the relative standard deviation (RSD) 2.54% (n = 6). In a study of interferences, the antimony-sensitive TGA-QD-BSA sensor showed good selectivity. Therefore, a simple, fast, sensitive, and highly selective assay for antimony has been built. The presented method has been applied successfully to the determination of antimony in real water samples (n = 6) with satisfactory results.

  18. Neutron detector

    DOEpatents

    Stephan, Andrew C.; Jardret; Vincent D.

    2011-04-05

    A neutron detector has a volume of neutron moderating material and a plurality of individual neutron sensing elements dispersed at selected locations throughout the moderator, and particularly arranged so that some of the detecting elements are closer to the surface of the moderator assembly and others are more deeply embedded. The arrangement captures some thermalized neutrons that might otherwise be scattered away from a single, centrally located detector element. Different geometrical arrangements may be used while preserving its fundamental characteristics. Different types of neutron sensing elements may be used, which may operate on any of a number of physical principles to perform the function of sensing a neutron, either by a capture or a scattering reaction, and converting that reaction to a detectable signal. High detection efficiency, an ability to acquire spectral information, and directional sensitivity may be obtained.

  19. Neutron detector

    SciTech Connect

    Stephan, Andrew C; Jardret, Vincent D

    2009-04-07

    A neutron detector has a volume of neutron moderating material and a plurality of individual neutron sensing elements dispersed at selected locations throughout the moderator, and particularly arranged so that some of the detecting elements are closer to the surface of the moderator assembly and others are more deeply embedded. The arrangement captures some thermalized neutrons that might otherwise be scattered away from a single, centrally located detector element. Different geometrical arrangements may be used while preserving its fundamental characteristics. Different types of neutron sensing elements may be used, which may operate on any of a number of physical principles to perform the function of sensing a neutron, either by a capture or a scattering reaction, and converting that reaction to a detectable signal. High detection efficiency, an ability to acquire spectral information, and directional sensitivity may be obtained.

  20. Angle detector

    NASA Technical Reports Server (NTRS)

    Parra, G. T. (Inventor)

    1978-01-01

    An angle detector for determining a transducer's angular disposition to a capacitive pickup element is described. The transducer comprises a pendulum mounted inductive element moving past the capacitive pickup element. The capacitive pickup element divides the inductive element into two parts L sub 1 and L sub 2 which form the arms of one side of an a-c bridge. Two networks R sub 1 and R sub 2 having a plurality of binary weighted resistors and an equal number of digitally controlled switches for removing resistors from the networks form the arms of the other side of the a-c bridge. A binary counter, controlled by a phase detector, balances the bridge by adjusting the resistance of R sub 1 and R sub 2. The binary output of the counter is representative of the angle.

  1. Flame Detector

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Scientific Instruments, Inc. has now developed a second generation, commercially available instrument to detect flames in hazardous environments, typically refineries, chemical plants and offshore drilling platforms. The Model 74000 detector incorporates a sensing circuit that detects UV radiation in a 100 degree conical field of view extending as far as 250 feet from the instrument. It operates in a bandwidth that makes it virtually 'blind' to solar radiation while affording extremely high sensitivity to ultraviolet flame detection. A 'windowing' technique accurately discriminates between background UV radiation and ultraviolet emitted from an actual flame, hence the user is assured of no false alarms. Model 7410CP is a combination controller and annunciator panel designed to monitor and control as many as 24 flame detectors. *Model 74000 is no longer being manufactured.

  2. A Si/CdTe Compton Camera for gamma-ray lens experiment

    NASA Astrophysics Data System (ADS)

    Takahashi, Tadayuki

    2005-12-01

    Cadmium telluride (CdTe) and cadmium zinc telluride (CdZnTe) have been regarded as promising semiconductor materials for hard X-ray and γ-ray detection. However, a considerable amount of charge loss in these detectors results in a reduced energy resolution. We have achieved a significant improvement in the spectral properties by forming the Schottky junction on the Te side of the CdTe wafer. With the further reduction of leakage current by an adoption of guard ring structure, we have demonstrated a CdTe pixel detector with high energy resolution and full charge collection capabilty. The detector has a pixel size of a few mm and a thickness of 0.5 - 1 mm. We apply this high resolution detector to a new silicon and CdTe Compton Camera which features high angular resolution. We also describe a concept of the stack detector which consists of many thin CdTe layers and provides sufficient efficiency for hard X-rays and gamma-rays up to several hundred keV maintaining good energy resolution. A narrow-FOV Compton telescope can be realized by installing a Si/CdTe Compton Camera inside the deep well of an active shield. This configuration is very suitable as focal plane detector for future focusing gamma-ray missions.

  3. Neutrino Detectors

    NASA Astrophysics Data System (ADS)

    von Feilitzsch, Franz; Lanfranchi, Jean-Côme; Wurm, Michael

    The neutrino was postulated by Wolfgang Pauli in the early 1930s, but could only be detected for the first time in the 1950s. Ever since scientists all around the world have worked on the detection and understanding of this particle which so scarcely interacts with matter. Depending on the origin and nature of the neutrino, various types of experiments have been developed and operated. In this entry, we will review neutrino detectors in terms of neutrino energy and associated detection technique as well as the scientific outcome of some selected examples. After a brief historical introduction, the detection of low-energy neutrinos originating from nuclear reactors or from the Earth is used to illustrate the principles and difficulties which are encountered in detecting neutrinos. In the context of solar neutrino spectroscopy, where the neutrino is used as a probe for astrophysics, three different types of neutrino detectors are presented - water Čerenkov, radiochemical, and liquid-scintillator detectors. Moving to higher neutrino energies, we discuss neutrinos produced by astrophysical sources and from accelerators. The entry concludes with an overview of a selection of future neutrino experiments and their scientific goals.

  4. Enhanced fluorescence from CdTe quantum dots self-assembled on the surface of silver nanoparticles.

    PubMed

    An, L M; Yang, Y Q; Su, W H; Yi, J; Liu, C X; Chao, K F; Zeng, Q H

    2010-03-01

    This paper presents an investigation on the fluorescent properties of semiconductor CdTe quantum dots (QDs) self-assembled on the surface of PVP (polyvinylpyrrolidone)-capped silver nanoparticles (NPs) by the ligand field effect. A significant 2.5-fold enhancement in the integrated fluorescence intensities, red shift of fluorescence peak, and obvious decrease of lifetime were observed in the CdTe QDs assembled on the Ag NPs in comparison with the pure CdTe QDs. The fluorescence enhancement factor and red shift were found to depend on the Ag NP concentration. The fluorescence enhancement was attributed to a highly localized electromagnetic field on the Ag NPs generated by the surface plasma and the change in the surface trap state of the CdTe QDs originating from plasma oscillations in the Ag NPs. It is first proposed that the surface passivation of CdTe QDs is also an important factor for metal-enhanced fluorescence. The surface defects of CdTe QDs can be modified by the Cd-O coordination interaction between the CdTe QDs and PVP molecules, which will cause the trap state density and luminescence lifetime to decrease. The surface passivation of CdTe QDs can also improve fluorescence quantum yield and lead to the red shift of the fluorescence peak. Compared with previous reports, the occurrence of the self-assembly of CdTe QDs on the surface of PVP-capped Ag NPs is fairly simple and easy. From a practical point of view, the combination of CdTe QDs with Ag NPs may lead to the fluorescence enhancement, which could be utilized in a variety of chemical and biological detection applications. PMID:20355634

  5. Characterization and evaluation of extended defects in CZT crystals for gamma-ray detectors

    NASA Astrophysics Data System (ADS)

    Bolotnikov, A. E.; Camarda, G. S.; Cui, Y.; Yang, G.; Hossain, A.; Kim, K.; James, R. B.

    2013-09-01

    Material homogeneity is critical in achieving high-performance in all types of radiation detectors. This requirement is not inevitably satisfied in today's commercial detector-grade CdZnTe (CZT) material because it contains high concentrations of extended defects, in particular, Te inclusions, dislocation networks, and twin- and subgrain-boundaries that affect the energy resolution and the efficiency of the devices. Defects, such as grain boundaries and cracks that completely block charge-carrier transport are impermissible in CZT radiation-detectors at concentrations exceeding certain threshold values. Our group in Brookhaven National Laboratory (BNL) conducts systematic studies, detailing the roles of crystal defects in CZT detectors and the mechanisms underlying their formation and effects. We employ infrared transmission microscopy, white beam X-ray diffraction topography, and high-spatial-resolution X-ray response mapping to identify particular types of defects and reveal their relationship with the devices' performances. In this article, we summarize some of the most important results that our group obtained over the past 5 years.

  6. Quantitative model of EBIC for CdTe

    NASA Astrophysics Data System (ADS)

    Haney, Paul; Yoon, Heayoung; Koirala, Prakash; Collins, Robert; Zhitenev, Nikolai

    2015-03-01

    Electron beam induced current (EBIC) is a powerful characterization technique which offers the high spatial resolution needed to study polycrystalline solar cells. In an EBIC experiment, a beam of high energy electrons excites electron-hole pairs, some fraction of which are collected by contacts. Ideally, an EBIC measurement reflects the spatially resolved quantum efficiency of the device. However, experiments on polycrystalline CdTe solar cells reveal that the EBIC collection efficiency is substantially lower than the quantum efficiency of the device under optical excitation. In order to reliably extract intrinsic material properties from EBIC signals, this difference must be reconciled. Two important differences between an EBIC experiment and normal device operation are: 1. the high generation rate density associated with the electron beam, and 2. the substantial effect of the exposed surface in an EBIC experiment. By developing numerical and analytical models which account for both of these effects, the difference in the material response under EBIC and normal device operation conditions can be understood. Comparison between the model and experiment show good agreement between quantities such as maximum EBIC collection efficiency versus charge generation rate.

  7. Structural and AC conductivity study of CdTe nanomaterials

    NASA Astrophysics Data System (ADS)

    Das, Sayantani; Banerjee, Sourish; Sinha, T. P.

    2016-04-01

    Cadmium telluride (CdTe) nanomaterials have been synthesized by soft chemical route using mercapto ethanol as a capping agent. Crystallization temperature of the sample is investigated using differential scanning calorimeter. X-ray diffraction and transmission electron microscope measurements show that the prepared sample belongs to cubic structure with the average particle size of 20 nm. Impedance spectroscopy is applied to investigate the dielectric relaxation of the sample in a temperature range from 313 to 593 K and in a frequency range from 42 Hz to 1.1 MHz. The complex impedance plane plot has been analyzed by an equivalent circuit consisting of two serially connected R-CPE units, each containing a resistance (R) and a constant phase element (CPE). Dielectric relaxation peaks are observed in the imaginary parts of the spectra. The frequency dependence of real and imaginary parts of dielectric permittivity is analyzed using modified Cole-Cole equation. The temperature dependence relaxation time is found to obey the Arrhenius law having activation energy ~0.704 eV. The frequency dependent conductivity spectra are found to follow the power law. The frequency dependence ac conductivity is analyzed by power law.

  8. Recombination by grain-boundary type in CdTe

    SciTech Connect

    Moseley, John Ahrenkiel, Richard K.; Metzger, Wyatt K.; Moutinho, Helio R.; Guthrey, Harvey L.; Al-Jassim, Mowafak M.; Paudel, Naba; Yan, Yanfa

    2015-07-14

    We conducted cathodoluminescence (CL) spectrum imaging and electron backscatter diffraction on the same microscopic areas of CdTe thin films to correlate grain-boundary (GB) recombination by GB “type.” We examined misorientation-based GB types, including coincident site lattice (CSL) Σ = 3, other-CSL (Σ = 5–49), and general GBs (Σ > 49), which make up ∼47%–48%, ∼6%–8%, and ∼44%–47%, respectively, of the GB length at the film back surfaces. Statistically averaged CL total intensities were calculated for each GB type from sample sizes of ≥97 GBs per type and were compared to the average grain-interior CL intensity. We find that only ∼16%–18% of Σ = 3 GBs are active non-radiative recombination centers. In contrast, all other-CSL and general GBs are observed to be strong non-radiative centers and, interestingly, these GB types have about the same CL intensity. Both as-deposited and CdCl{sub 2}-treated films were studied. The CdCl{sub 2} treatment reduces non-radiative recombination at both other-CSL and general GBs, but GBs are still recombination centers after the CdCl{sub 2} treatment.

  9. Pixellated thallium bromide detectors for gamma-ray spectroscopy and imaging

    NASA Astrophysics Data System (ADS)

    Onodera, T.; Hitomi, K.; Shoji, T.; Hiratate, Y.

    2004-06-01

    Recently, pixellated semiconductor detectors exhibit high-energy resolution, which have been studied actively and fabricated from CdTe, CZT and HgI 2. Thallium bromide (TlBr) is a compound semiconductor characterized with its high atomic numbers (Tl=81, Br=35) and high density (7.56 g/cm 3). Thus, TlBr exhibits higher photon stopping power than other semiconductor materials used for radiation detector fabrication such as CdTe, CZT and HgI 2. The wide band gap of TlBr (2.68 eV) permits the detectors low-noise operation at around room temperature. Our studies made an effort to fabricate pixellated TlBr detectors had sufficient detection efficiency and good charge collection efficiency. In this study, pixellated TlBr detectors were fabricated from the crystals purified by the multipass zone-refining method and grown by the horizontal traveling molten zone (TMZ) method. The TlBr detector has a continuous cathode over one crystal surface and 3×3 pixellated anodes (0.57×0.57 mm 2 each) surrounded by a guard ring on the opposite surface. The electrodes were realized by vacuum evaporation of palladium through a shadow mask. Typical thickness of the detector was 2 mm. Spectrometric performance of the TlBr detectors was tested by irradiating them with 241Am (59.5 keV), 57Co (122 keV) and 137Cs (662 keV) gamma-ray sources at temperature of -20°C. Energy resolutions (FWHM) were measured to be 4.0, 6.0 and 9.7 keV for 59.5, 122 and 662 keV gamma-rays, respectively.

  10. Far-infrared spectroscopy of CdTe1-xSex(In): Phonon properties

    NASA Astrophysics Data System (ADS)

    Petrović, M.; Romčević, N.; Trajić, J.; Dobrowolski, W. D.; Romčević, M.; Hadžić, B.; Gilić, M.; Mycielski, A.

    2014-11-01

    The far-infrared reflectivity spectra of CdTe0.97Se0.03 and CdTe0.97Se0.03(In) single crystals were measured at different temperatures. The analysis of the far-infrared spectra was carried out by a fitting procedure based on the dielectric function which includes spatial distribution of free carriers as well as their influence on the plasmon-phonon interaction. We found that the long wavelength optical phonon modes of CdTe1-xSex mixed crystals exhibit a two-mode behavior. The local In mode at about 160 cm-1 is observed. In both sample, a surface layer with a low concentration of free carriers (depleted region) are formed.

  11. Advances in the In-House CdTe Research Activities at NREL

    SciTech Connect

    Gessert, T.; Wu, X.; Dhere, R.; Moutinho, H.; Smith, S.; Romero, M.; Zhou, J.; Duda, A.; Corwine, C.

    2005-01-01

    NREL in-house CdTe research activities have impacted a broad range of recent program priorities. Studies aimed at industrially relevant applications have produced new materials and processes that enhance the performance of devices based on commercial materials (e.g., soda-lime glass, SnO2:F). Preliminary tests of the effectiveness of these novel components using large-scale processes have been encouraging. Similarly, electro- and nano-probe techniques have been developed and used to study the evolution and function of CdTe grain boundaries. Finally, cathodoluminescence (CL) and photoluminescence (PL) studies on single-crystal samples have yielded improved understanding of how various processes may combine to produce important defects in CdTe films.

  12. Stability of CdTe solar cells at elevated temperatures: Bias, temperature, and Cu dependence

    NASA Astrophysics Data System (ADS)

    Hiltner, Jason F.; Sites, James R.

    1999-03-01

    A systematic study of the stability of CdTe solar cells fabricated by SCI and NREL has been made. Cells were stressed at elevated temperatures under various bias conditions, both with illumination (˜2 suns) and in the dark. An activation energy of approximately 1 eV is implied from cells stressed at various elevated temperatures. The stability of CdTe solar cells was found to be bias dependent and device-specific. Cells made with thick CdTe and no back-contact copper as well as by at least one SCI recipe were very stable. Extrapolation of effects assuming Arrhenius behavior yields estimated lifetime expectations for the cells stressed at elevated temperatures.

  13. Optimization of material/device parameters of CdTe photovoltaic for solar cells applications

    NASA Astrophysics Data System (ADS)

    Wijewarnasuriya, Priyalal S.

    2016-05-01

    Cadmium telluride (CdTe) has been recognized as a promising photovoltaic material for thin-film solar cell applications due to its near optimum bandgap of ~1.5 eV and high absorption coefficient. The energy gap is near optimum for a single-junction solar cell. The high absorption coefficient allows films as thin as 2.5 μm to absorb more than 98% of the above-bandgap radiation. Cells with efficiencies near 20% have been produced with poly-CdTe materials. This paper examines n/p heterostructure device architecture. The performance limitations related to doping concentrations, minority carrier lifetimes, absorber layer thickness, and surface recombination velocities at the back and front interfaces is assessed. Ultimately, the paper explores device architectures of poly- CdTe and crystalline CdTe to achieve performance comparable to gallium arsenide (GaAs).

  14. Controlled optical properties of water-soluble CdTe nanocrystals via anion exchange.

    PubMed

    Li, Jing; Jia, Jianguang; Lin, Yuan; Zhou, Xiaowen

    2016-02-01

    We report a study on anion exchange reaction of CdTe nanocrystals with S(2-) in aqueous solution under ambient condition. We found that the optical properties of CdTe nanocrystals can be well tuned by controlling the reaction conditions, in which the reaction temperature is crucially important. At low reaction temperature, the product nanocrystals showed blue-shifts in both absorption and PL spectra, while the photoluminescence quantum yield (PLQY) was significantly enhanced. When anion exchanges were carried out at higher reaction temperature, on the other hand, obvious red shifts in absorption and PL spectra accompanied by a fast increase followed by gradual decrease in PLQY were observed. On variation of S(2-) concentration, it was found that the overall kinetics of Te(2-) for S(2-) exchanges depends also on [S(2-)] when anion exchanges were performed at higher temperature. A possible mechanism for anion exchanges in CdTe NCs was proposed. PMID:26520812

  15. Sulfur diffusion in polycrystalline thin-film CdTe solar cells

    SciTech Connect

    Aslan, M.H.; Song, W.; Tang, T.; Mao, D.; Collins, R.T.; Levi, D.H.; Ahrenkiel, R.K.; Lindstrom, S.C.; Johnson, M.B.

    1998-12-31

    X-ray diffraction and photoluminescence measurements have been used to characterize the diffusion of S into CdTe during post growth annealing of CdTe solar cells. For anneals at 410 C in the presence of CdCl{sub 2}, evidence that both a CdTe{sub 1{minus}x}S{sub x} phase and nearly-pure CdTe are present near the back contact is observed. The ternary phase becomes more prominent and the S concentration increases with depth reaching roughly 4--5% near the CdS interface. Much less diffusion is observed at 350 C while for a 460 C anneal, CdTe{sub 1{minus}x}S{sub x} with a S concentration near 5% is found throughout the layer. The presence of CdCl{sub 2} during the anneal enhances the interdiffusion.

  16. High resistivity in undoped CdTe: carrier compensation of Te antisites and Cd vacancies

    NASA Astrophysics Data System (ADS)

    Lindström, A.; Mirbt, S.; Sanyal, B.; Klintenberg, M.

    2016-01-01

    In this paper, we focus on the high resistivity of intentionally undoped CdTe, where the most prevalent defects are Cd vacancies and Te antisites. Our calculated formation energies lead to the conclusion that the Fermi energy of undoped CdTe is at midgap due to carrier compensation of Te antisites and Cd vacancies, which explains the experimentally observed high resistivity. We use density functional theory with the hybrid functional of Heyd, Scuseria and Ernzerhof (HSE06) and show that the proper description of the native defects in general fails using the local density approximation (LDA) instead of HSE06. We conclude that LDA is insufficient to understand the high resistivity of undoped CdTe. We calculate the neutral and double acceptor state of the Te antisite to be intrinsic DX-centers.

  17. Controlled optical properties of water-soluble CdTe nanocrystals via anion exchange.

    PubMed

    Li, Jing; Jia, Jianguang; Lin, Yuan; Zhou, Xiaowen

    2016-02-01

    We report a study on anion exchange reaction of CdTe nanocrystals with S(2-) in aqueous solution under ambient condition. We found that the optical properties of CdTe nanocrystals can be well tuned by controlling the reaction conditions, in which the reaction temperature is crucially important. At low reaction temperature, the product nanocrystals showed blue-shifts in both absorption and PL spectra, while the photoluminescence quantum yield (PLQY) was significantly enhanced. When anion exchanges were carried out at higher reaction temperature, on the other hand, obvious red shifts in absorption and PL spectra accompanied by a fast increase followed by gradual decrease in PLQY were observed. On variation of S(2-) concentration, it was found that the overall kinetics of Te(2-) for S(2-) exchanges depends also on [S(2-)] when anion exchanges were performed at higher temperature. A possible mechanism for anion exchanges in CdTe NCs was proposed.

  18. Preliminary characterisation of CdTe M-π-n diode structures

    NASA Astrophysics Data System (ADS)

    Greiffenberg, D.; Fauler, A.; Zwerger, A.; Baumbach, T.; Fiederle, M.

    2011-05-01

    Due to the high Z, 1 mm CdTe (Z=52, 48) offers a high absorption probability for photons with energies up to 100 keV [1] (Zwerger and Fiederle, 2007). In order to further reduce the dark current flowing through the sensor when applying high voltage, CdTe diode structures (M-π-n) have been processed at the Freiburg Materials Research Center (FMF). As comparison, CdTe sensors with ohmic contacts, working as photoresistors have also been produced. The different sensor structures have been flip-chip bonded on Medipix2 readout electronics [5] (Llopart and Campbell, 2002). This work reports on the I-V characteristics of the different sensor structures, confirming the improved leakage current flowing through the diode structure. Furthermore, the imaging capabilities of the diode structures with respect to their spatial resolution are presented.

  19. Hard X-ray and γ-ray detectors for the NeXT mission

    NASA Astrophysics Data System (ADS)

    Takahashi, Tadayuki; Makishima, Kazuo; Fukazawa, Yasushi; Kokubun, Motohide; Nakazawa, Kazuhiro; Nomachi, Masaharu; Tajima, Hiroyasu; Tashiro, Makoto; Terada, Yukikatsu

    2004-02-01

    When compared with X-ray astronomy, the γ-ray astronomy, especially in the energy band from 10 keV to several MeV, is still immature and significant improvements should be done to obtain sensitivity comparable to that achieved in the energy band below 10 keV. In order to fill this "sensitivity gap", the NeXT (New X-ray Telescope) mission has been proposed as a successor of the Astro-E2 mission. The high-energy response of the super mirror will enable us to perform first sensitive imaging observation up to 80 keV. One idea for the focal plane detector is to combine a fully depleted X-ray imaging device (soft X-ray detector) and a pixelated CdTe (cadmium telluride) detector. In the soft γ-ray band upto ˜1 MeV, a narrow field-of-view Compton γ-ray telescope utilizing several tens of layers of thin Si or CdTe detector has been proposed to obtain much higher sensitivity than present instruments.

  20. Studies on optoelectronic properties of DC reactive magnetron sputtered CdTe thin films

    NASA Astrophysics Data System (ADS)

    Kumar, B. Rajesh; Hymavathi, B.; Rao, T. Subba

    2014-01-01

    Cadmium telluride continues to be a leading candidate for the development of cost effective photovoltaics for terrestrial applications. In the present work two individual metallic targets of Cd and Te were used for the deposition of CdTe thin films on mica substrates from room temperature to 300 °C by DC reactive magnetron sputtering method. XRD patterns of CdTe thin films deposited on mica substrates exhibit peaks at 2θ = 27.7°, 46.1° and 54.6°, which corresponds to reflection on (1 1 1), (2 2 0) and (3 1 1) planes of CdTe cubic structure. The intensities of XRD patterns increases with the increase of substrate temperature upto 150 °C and then it decreases at higher substrate temperatures. The conductivity of CdTe thin films measured from four probe method increases with the increase of substrate temperature. The activation energies (ΔE) are found to be decrease with the increase of substrate temperature. The optical transmittance spectra of CdTe thin films deposited on mica have a clear interference pattern in the longer wavelength region. The films have good transparency (T > 85 %) exhibiting interference pattern in the spectral region between 1200 - 2500 nm. The optical band gap of CdTe thin films are found to be in the range of 1.48 - 1.57. The refractive index, n decreases with the increase of wavelength, λ. The value of n and k increases with the increase of substrate temperature.

  1. Development of Substrate Structure CdTe Photovoltaic Devices with Performance Exceeding 10%: Preprint

    SciTech Connect

    Dhere, R. G.; Duenow, J. N.; DeHart, C. M.; Li, J. V.; Kuciauskas, D.; Gessert, T. A.

    2012-08-01

    Most work on CdTe-based solar cells has focused on devices with a superstrate structure. This focus is due to the early success of the superstrate structure in producing high-efficiency cells, problems of suitable ohmic contacts for lightly doped CdTe, and the simplicity of the structure for manufacturing. The development of the CdCl2 heat treatment boosted CdTe technology and perpetuated the use of the superstrate structure. However, despite the beneficial attributes of the superstrate structure, devices with a substrate structure are attractive both commercially and scientifically. The substrate structure eliminates the need for transparent superstrates and thus allows the use of flexible metal and possibly plastic substrates. From a scientific perspective, it allows better control in forming the junction and direct access to the junction for detailed analysis. Research on such devices has been limited. The efficiency of these devices has been limited to around 8% due to low open-circuit voltage (Voc) and fill factor. In this paper, we present our recent device development efforts at NREL on substrate-structure CdTe devices. We have found that processing parameters required to fabricate high-efficiency substrate CdTe PV devices differ from those necessary for traditional superstrate CdTe devices. We have worked on a variety of contact materials including Cu-doped ZnTe and CuxTe. We will present a comparative analysis of the performance of these contacts. In addition, we have studied the influence of fabrication parameters on junction properties. We will present an overview of our development work, which has led to CdTe devices with Voc values of more than 860 mV and NREL-confirmed efficiencies approaching 11%.

  2. Phosphorus Diffusion Mechanisms and Deep Incorporation in Polycrystalline and Single-Crystalline CdTe

    NASA Astrophysics Data System (ADS)

    Colegrove, Eric; Harvey, Steven P.; Yang, Ji-Hui; Burst, James M.; Albin, David S.; Wei, Su-Huai; Metzger, Wyatt K.

    2016-05-01

    A key challenge in cadmium-telluride (CdTe) semiconductors is obtaining stable and high hole density. Group-I elements substituting Cd can form acceptors but easily self-compensate and diffuse quickly. For example, CdTe photovoltaics have relied on copper as a dopant, but this creates stability problems and hole density that has not exceeded 1015 cm-3 . If hole density can be increased beyond 1016 cm-3 , CdTe solar technology can exceed multicrystalline silicon performance and provide levelized costs of electricity below conventional energy sources. Group-V elements substituting Te offer a solution, but they are very difficult to incorporate. Using time-of-flight secondary-ion mass spectrometry, we examine bulk and grain-boundary diffusion of phosphorus (P) in CdTe in Cd-rich conditions. We find that in addition to slow bulk diffusion and fast grain-boundary diffusion, there is a critical fast bulk-diffusion component that enables deep P incorporation in CdTe. Detailed first-principle calculations indicate the slow bulk-diffusion component is caused by substitutional P diffusion through the Te sublattice, whereas the fast bulk-diffusion component is caused by P diffusing through interstitial lattice sites following the combination of a kick-out step and two rotation steps. The latter is limited in magnitude by high formation energy, but is sufficient to manipulate P incorporation. In addition to an increased physical understanding, these results open up experimental possibilities for group-V doping in CdTe applications.

  3. Long-term exposure to CdTe quantum dots causes functional impairments in live cells.

    PubMed

    Cho, Sung Ju; Maysinger, Dusica; Jain, Manasi; Röder, Beate; Hackbarth, Steffen; Winnik, Françoise M

    2007-02-13

    Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution.

  4. Effect of shells on photoluminescence of aqueous CdTe quantum dots

    SciTech Connect

    Yuan, Zhimin; Yang, Ping

    2013-07-15

    Graphical abstract: Size-tunable CdTe coated with several shells using an aqueous solution synthesis. CdTe/CdS/ZnS quantum dots exhibited high PL efficiency up to 80% which implies the promising applications for biomedical labeling. - Highlights: • CdTe quantum dots were fabricated using an aqueous synthesis. • CdS, ZnS, and CdS/ZnS shells were subsequently deposited on CdTe cores. • Outer ZnS shells provide an efficient confinement of electron and hole inside the QDs. • Inside CdS shells can reduce the strain on the QDs. • Aqueous CdTe/CdS/ZnS QDs exhibited high stability and photoluminescence efficiency of 80%. - Abstract: CdTe cores with various sizes were fabricated in aqueous solutions. Inorganic shells including CdS, ZnS, and CdS/ZnS were subsequently deposited on the cores through a similar aqueous procedure to investigate the effect of shells on the photoluminescence properties of the cores. In the case of CdTe/CdS/ZnS quantum dots, the outer ZnS shell provides an efficient confinement of electron and hole wavefunctions inside the quantum dots, while the middle CdS shell sandwiched between the CdTe core and ZnS shell can be introduced to obviously reduce the strain on the quantum dots because the lattice parameters of CdS is situated at the intermediate-level between those of CdTe and ZnS. In comparison with CdTe/ZnS core–shell quantum dots, the as-prepared water-soluble CdTe/CdS/ZnS quantum dots in our case can exhibit high photochemical stability and photoluminescence efficiency up to 80% in an aqueous solution, which implies the promising applications in the field of biomedical labeling.

  5. Studies on optoelectronic properties of DC reactive magnetron sputtered CdTe thin films

    SciTech Connect

    Kumar, B. Rajesh; Hymavathi, B.; Rao, T. Subba

    2014-01-28

    Cadmium telluride continues to be a leading candidate for the development of cost effective photovoltaics for terrestrial applications. In the present work two individual metallic targets of Cd and Te were used for the deposition of CdTe thin films on mica substrates from room temperature to 300 °C by DC reactive magnetron sputtering method. XRD patterns of CdTe thin films deposited on mica substrates exhibit peaks at 2θ = 27.7°, 46.1° and 54.6°, which corresponds to reflection on (1 1 1), (2 2 0) and (3 1 1) planes of CdTe cubic structure. The intensities of XRD patterns increases with the increase of substrate temperature upto 150 °C and then it decreases at higher substrate temperatures. The conductivity of CdTe thin films measured from four probe method increases with the increase of substrate temperature. The activation energies (ΔE) are found to be decrease with the increase of substrate temperature. The optical transmittance spectra of CdTe thin films deposited on mica have a clear interference pattern in the longer wavelength region. The films have good transparency (T > 85 %) exhibiting interference pattern in the spectral region between 1200 – 2500 nm. The optical band gap of CdTe thin films are found to be in the range of 1.48 – 1.57. The refractive index, n decreases with the increase of wavelength, λ. The value of n and k increases with the increase of substrate temperature.

  6. Correlated analysis of 2 MeV proton-induced radiation damage in CdZnTe crystals using photoluminescence and thermally stimulated current techniques

    NASA Astrophysics Data System (ADS)

    Gu, Yaxu; Jie, Wanqi; Rong, Caicai; Wang, Yuhan; Xu, Lingyan; Xu, Yadong; Lv, Haoyan; Shen, Hao; Du, Guanghua; Fu, Xu; Guo, Na; Zha, Gangqiang; Wang, Tao

    2016-11-01

    Radiation damage induced by 2 MeV protons in CdZnTe crystals has been studied by means of photoluminescence (PL) and thermally stimulated current (TSC) techniques. A notable quenching of PL intensity is observed in the regions irradiated with a fluence of 6 × 1013 p/cm2, suggesting the increase of non-radiative recombination centers. Moreover, the intensity of emission peak Dcomplex centered at 1.48 eV dominates in the PL spectrum obtained from irradiated regions, ascribed to the increase of interstitial dislocation loops and A centers. The intensity of TSC spectra in irradiated regions decreases compared to the virgin regions, resulting from the charge collection inefficiency caused by proton-induced recombination centers. By comparing the intensity of identified traps obtained from numerical fitting using simultaneous multiple peak analysis (SIMPA) method, it suggests that proton irradiation under such dose can introduce high density of dislocation and A-centers in CdZnTe crystals, consistent with PL results.

  7. Improved spectrometric characteristics of thallium bromide nuclear radiation detectors

    NASA Astrophysics Data System (ADS)

    Hitomi, K.; Murayama, T.; Shoji, T.; Suehiro, T.; Hiratate, Y.

    1999-06-01

    Thallium bromide (TlBr) is a compound semiconductor with a high atomic number and wide band gap. In this study, nuclear radiation detectors have been fabricated from the TlBr crystals. The TlBr crystals were grown by the horizontal travelling molten zone (TMZ) method using the materials purified by many pass zone refining. The crystals were characterized by measuring the resistivity, the mobility-lifetime ( μτ) product and the energy required to create an electron-hole pair (the ɛ value). Improved energy resolution has been obtained by the TlBr radiation detectors. At room temperature the full-width at half-maximum (FWHM) for the 59.5, 122 and 662 keV γ-ray photo peak obtained from the detectors were 3.3, 8.8 and 29.5 keV, respectively. By comparing the saturated peak position of the TlBr detector with that of the CdTe detector, the ɛ value has been estimated to be about 5.85 eV for the TlBr crystal.

  8. Rf sputtering of CdTE and CdS for thin film PV

    NASA Astrophysics Data System (ADS)

    Compaan, A. D.; Tabory, C. N.; Shao, M.; Fischer, A.; Feng, Z.; Bohn, R. G.

    1994-06-01

    In late 1992 we demonstrated the first rf sputtered CdS/CdTe photovoltaic cell with efficiency exceeding 10%. In this cell both CdS and CdTe layers were deposited by rf sputtering. In this paper we report preliminary measurements of 1) optical emission spectroscopy of the rf plasma, 2) the width of the phonon Raman line as a function of deposition temperature for CdS, and 3) studies of oxygen doping during pulsed laser deposition of CdTe.

  9. Long Lifetime Hole Traps at Grain Boundaries in CdTe Thin-Film Photovoltaics.

    PubMed

    Mendis, B G; Gachet, D; Major, J D; Durose, K

    2015-11-20

    A novel time-resolved cathodoluminescence method, where a pulsed electron beam is generated via the photoelectric effect, is used to probe individual CdTe grain boundaries. Excitons have a short lifetime (≤100 ps) within the grains and are rapidly quenched at the grain boundary. However, a ~47 meV shallow acceptor, believed to be due to oxygen, can act as a long lifetime hole trap, even at the grain boundaries where their concentration is higher. This provides direct evidence supporting recent observations of hopping conduction across grain boundaries in highly doped CdTe at low temperature. PMID:26636877

  10. Long Lifetime Hole Traps at Grain Boundaries in CdTe Thin-Film Photovoltaics

    NASA Astrophysics Data System (ADS)

    Mendis, B. G.; Gachet, D.; Major, J. D.; Durose, K.

    2015-11-01

    A novel time-resolved cathodoluminescence method, where a pulsed electron beam is generated via the photoelectric effect, is used to probe individual CdTe grain boundaries. Excitons have a short lifetime (≤100 ps ) within the grains and are rapidly quenched at the grain boundary. However, a ˜47 meV shallow acceptor, believed to be due to oxygen, can act as a long lifetime hole trap, even at the grain boundaries where their concentration is higher. This provides direct evidence supporting recent observations of hopping conduction across grain boundaries in highly doped CdTe at low temperature.

  11. Characterizing Recombination in CdTe Solar Cells with Time-Resolved Photoluminescence: Preprint

    SciTech Connect

    Metzger, W. K.; Romero, M. J.; Dippo, P.; Young, M.

    2006-05-01

    Time-resolved photoluminescence (TRPL) computer simulations demonstrate that under certain experimental conditions it is possible to assess recombination in CdTe solar cells in spite of the junction. This is supported by experimental findings that open-circuit voltage (Voc) is dependent on lifetime in a manner consistent with device theory. Measurements on inverted structures show that the CdCl2 treatment significantly reduces recombination in the CdTe layer without S diffusion. However, S diffusion is required for lifetimes comparable to those observed in high-efficiency solar cells. The results indicate that substrate solar cells can be fabricated with recombination lifetimes similar to superstrate cells.

  12. Dust Detector

    NASA Technical Reports Server (NTRS)

    Kelley, M. C.

    2001-01-01

    We discuss a recent sounding rocket experiment which found charged dust in the Earth's tropical mesosphere. The dust detector was designed to measure small (5000 - 10000 amu.) charged dust particles, most likely of meteoric origin. A 5 km thick layer of positively charged dust was found at an altitude of 90 km, in the vicinity of an observed sporadic sodium layer and sporadic E layer. The observed dust was positively charged in the bulk of the dust layer, but was negatively charged near the bottom.

  13. Ion detector

    DOEpatents

    Tullis, Andrew M.

    1987-01-01

    An improved ion detector device of the ionization detection device chamber ype comprises an ionization chamber having a central electrode therein surrounded by a cylindrical electrode member within the chamber with a collar frictionally fitted around at least one of the electrodes. The collar has electrical contact means carried in an annular groove in an inner bore of the collar to contact the outer surface of the electrode to provide electrical contact between an external terminal and the electrode without the need to solder leads to the electrode.

  14. Structural, optical and photovoltaic properties of co-doped CdTe QDs for quantum dots sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Ayyaswamy, Arivarasan; Ganapathy, Sasikala; Alsalme, Ali; Alghamdi, Abdulaziz; Ramasamy, Jayavel

    2015-12-01

    Zinc and sulfur alloyed CdTe quantum dots (QDs) sensitized TiO2 photoelectrodes have been fabricated for quantum dots sensitized solar cells. Alloyed CdTe QDs were prepared in aqueous phase using mercaptosuccinic acid (MSA) as a capping agent. The influence of co-doping on the structural property of CdTe QDs was studied by XRD analysis. The enhanced optical absorption of alloyed CdTe QDs was studied using UV-vis absorption and fluorescence emission spectra. The capping of MSA molecules over CdTe QDs was confirmed by the FTIR and XPS analyses. Thermogravimetric analysis confirms that the prepared QDs were thermally stable up to 600 °C. The photovoltaic performance of alloyed CdTe QDs sensitized TiO2 photoelectrodes were studied using J-V characteristics under the illumination of light with 1 Sun intensity. These results show the highest photo conversion efficiency of η = 1.21%-5% Zn & S alloyed CdTe QDs.

  15. MBE-Grown CdTe Layers on GaAs with In-assisted Thermal Deoxidation

    NASA Astrophysics Data System (ADS)

    Arı, Ozan; Bilgilisoy, Elif; Ozceri, Elif; Selamet, Yusuf

    2016-10-01

    Molecular beam epitaxy (MBE) growth of thin (˜2 μm) CdTe layers characterized by high crystal quality and low defect density on lattice mismatched substrates, such as GaAs and Si, has thus far been difficult to achieve. In this work, we report the effects of in situ thermal deoxidation under In and As4 overpressure prior to the CdTe growth on epiready GaAs(211)B wafers, aiming to enhance CdTe crystal quality. Thermally deoxidized GaAs samples were analyzed using in situ reflection high energy electron diffraction, along with ex situ x-ray photo-electron spectroscopy (XPS) and atomic force microscopy. MBE-grown CdTe layers were characterized using x-ray diffraction (XRD) and Everson-type wet chemical defect decoration etching. We found that In-assisted desorption allowed for easier surface preparation and resulted in a smoother surface compared to As-assisted surface preparation. By applying In-assisted thermal deoxidation to GaAs substrates prior to the CdTe growth, we have obtained single crystal CdTe films with a CdTe(422) XRD rocking curve with a full-width half-maximum value of 130.8 arc-s and etch pit density of 4 × 106 cm-2 for 2.54 μm thickness. We confirmed, by XPS analysis, no In contamination on the thermally deoxidized surface.

  16. Optical and electrical characterizations of highly efficient CdTe thin film solar cells prepared by close-spaced sublimation

    NASA Astrophysics Data System (ADS)

    Okamoto, T.; Yamada, A.; Konagai, M.

    2000-06-01

    The effects of the Cu diffusion on the optical and electrical properties of CdTe thin film solar cells prepared by close-spaced sublimation (CSS) were investigated by capacitance-voltage ( C- V) measurement and low-temperature photoluminescence (PL) measurement. C- V measurement revealed that the net acceptor concentration in the CdTe layer was independent of the heat treatment after screen printing of the Cu-doped graphite electrode for Cu diffusion into the CdTe layer, although it greatly affected the solar cell performance. Furthermore, the depth profile of PL spectrum of CdTe layer implies that the heat treatment for Cu diffusion facilitates the formation of low-resistance contact to CdTe through the formation of a heavily doped (p +) region in the CdTe adjacent to the back electrode, but Cu atoms do not act as effective acceptors in the CdTe layer except the region near the back electrode.

  17. Band structure and Optical properties CdTe and CdSn3Te4 thin films

    NASA Astrophysics Data System (ADS)

    Venkatachalam, T.; Velumani, S.; Ganesan, S.; Sakthivel, K.

    2008-04-01

    CdTe and CdSn3Te4 compounds were prepared by direct reaction of their high purity elemental constituents using rotating furnace. Optimal deposition conditions for the deposition of CdTe and CdSn3Te4 thin films in hot wall evaporation setup were simulated using Monte Carlo technique. Thin films of CdTe and CdSn3Te4 were deposited on glass substrates by hot wall evaporation method. From the XRD measurements it was found that the films of CdTe and CdSn3Te4 were of cubic zinc-blende and rock salt structures respectively. The lattice parameters were determined as a = 6.476 Å (CdTe) and a = 6.238 Å (CdSn3Te4) from the XRD data. The UV-Vis-NIR optical transmittance spectra of thin films of different films were obtained and it was found that the direct optical band gaps were 1.4 eV (CdTe) and 0.8 eV (CdSn3Te4). Electronic structure, band parameters and optical spectra of CdTe and CdSn3Te4 were calculated from ab initio studies within the GGA approximation. The experimental results were in good agreement with the theoretical values.

  18. Cooperative antimicrobial activity of CdTe quantum dots with rocephin and fluorescence monitoring for Escherichia coli.

    PubMed

    Luo, Zhihui; Wu, Qingsheng; Zhang, Meng; Li, Ping; Ding, Yaping

    2011-10-01

    In this study, the cooperative antibacterial efficiency of CdTe quantum dots (QDs) and rocephin against Escherichia coli (E. coli) was investigated. Colony-forming capability assay and diameter of inhibition zone (DIZ) measurement showed the antibiotic action of CdTe QDs-rocephin complex was better than the superposition of pure CdTe QDs and rocephin. The fractional inhibitory concentration index (FICI) indicated that CdTe QDs-rocephin complex could achieve great cooperative antimicrobial effects. The infrared ray (IR) spectrum, photoluminescence (PL) spectrophotometry, and detection of reactive oxygen species (ROS) indicated that CdTe QDs and rocephin formed a stable antimicrobial group through electrostatic attraction and hydrogen bonds and then killed the E. coli together. Meanwhile, the fluorescence intensity of CdTe QDs and the optical density (OD) value of E. coli showed a good linear relationship. Thus, dynamic monitoring to total bacterial concentration in the antibacterial process was realized by the CdTe QDs.

  19. Oscillator detector

    SciTech Connect

    Potter, B.M.

    1980-05-13

    An alien liquid detector employs a monitoring element and an oscillatory electronic circuit for maintaining the temperature of the monitoring element substantially above ambient temperature. The output wave form, eg., frequency of oscillation or wave shape, of the oscillatory circuit depends upon the temperaturedependent electrical characteristic of the monitoring element. A predetermined change in the output waveform allows water to be discriminated from another liquid, eg., oil. Features of the invention employing two thermistors in two oscillatory circuits include positioning one thermistor for contact with water and the other thermistor above the oil-water interface to detect a layer of oil if present. Unique oscillatory circuit arrangements are shown that achieve effective thermistor action with an economy of parts and energizing power. These include an operational amplifier employed in an astable multivibrator circuit, a discrete transistor-powered tank circuit, and use of an integrated circuit chip.

  20. Analysis of electroluminescence images in small-area circular CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Bokalič, Matevž; Raguse, John; Sites, James R.; Topič, Marko

    2013-09-01

    The electroluminescence (EL) imaging process of small area solar cells is investigated in detail to expose optical and electrical effects that influence image acquisition and corrupt the acquired image. An approach to correct the measured EL images and to extract the exact EL radiation as emitted from the photovoltaic device is presented. EL images of circular cadmium telluride (CdTe) solar cells are obtained under different conditions. The power-law relationship between forward injection current and EL emission and a negative temperature coefficient of EL radiation are observed. The distributed Simulation Program with Integrated Circuit Emphasis (SPICE®) model of the circular CdTe solar cell is used to simulate the dark J-V curve and current distribution under the conditions used during EL measurements. Simulation results are presented as circularly averaged EL intensity profiles, which clearly show that the ratio between resistive parameters determines the current distribution in thin-film solar cells. The exact resistance values for front and back contact layers and for CdTe bulk layer are determined at different temperatures, and a negative temperature coefficient for the CdTe bulk resistance is observed.

  1. Spray Deposition of High Quality CuInSe2 and CdTe Films: Preprint

    SciTech Connect

    Curtis, C. J.; van Hest, M.; Miedaner, A.; Leisch, J.; Hersh, P.; Nekuda, J.; Ginley, D. S.

    2008-05-01

    A number of different ink and deposition approaches have been used for the deposition of CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS), and CdTe films. For CIS and CIGS, soluble precursors containing Cu, In, and Ga have been developed and used in two ways to produce CIS films. In the first, In-containing precursor films were sprayed on Mo-coated glass substrates and converted by rapid thermal processing (RTP) to In2Se3. Then a Cu-containing film was sprayed down on top of the In2Se3 and the stacked films were again thermally processed to give CIS. In the second approach, the Cu-, In-, and Ga-containing inks were combined in the proper ratio to produce a mixed Cu-In-Ga ink that was sprayed on substrates and thermally processed to give CIGS films directly. For CdTe deposition, ink consisting of CdTe nanoparticles dispersed in methanol was prepared and used to spray precursor films. Annealing these precursor films in the presence of CdCl2 produced large-grained CdTe films. The films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Optimized spray and processing conditions are crucial to obtain dense, crystalline films.

  2. Controllable synthesis of thiol-capped CdTe nanoparticles for optical sensing of triethylenetetramine dihydrochloride.

    PubMed

    Huy, Bui The; Kumar, Avvaru Praveen; Seo, Min-Ho; Kim, Jan-Di; Lee, Yong-Ill

    2014-10-01

    Highly luminescent CdTe quantum dots (QDs) were synthesized through a co-precipitation route in aqueous salt solutions using different thiols as stabilizers. The synthetic procedure was simple, efficient, and stable. It could also allow controlling the emission wavelength by varying the experimental conditions such as reaction time and pH values. The strong luminescence of the QDs was observed under UV-excitation and emission colors could be adjusted. The interaction between CdTe QDs and triethylenetetramine dihydrochloride (TETA) which is a candidate treatment for diabetic cardiovascular complication was investigated by fluorescence spectroscopy. Based on the quenching effect on CdTe photoluminescence intensity by TETA, a simple assay system for analyzing the content of TETA in aqueous samples was developed. The linearity was maintained in the range of 0.2 μM to 1.2 μM (R2 = 0.994) with a limit of detection (LOD; S/N = 3) at 28 nM. The results showed that CdTe QDs capped with diverse thiols has a potential for the quantitative analysis of TETA in urine samples.

  3. Interfacial charge transfer between CdTe quantum dots and Gram negative vs. Gram positive bacteria.

    SciTech Connect

    Dumas, E.; Gao, C.; Suffern, D.; Bradforth, S. E.; Dimitrejevic, N. M.; Nadeau, J. L.; McGill Univ.; Univ. of Southern California

    2010-01-01

    Oxidative toxicity of semiconductor and metal nanomaterials to cells has been well established. However, it may result from many different mechanisms, some requiring direct cell contact and others resulting from the diffusion of reactive species in solution. Published results are contradictory due to differences in particle preparation, bacterial strain, and experimental conditions. It has been recently found that C{sub 60} nanoparticles can cause direct oxidative damage to bacterial proteins and membranes, including causing a loss of cell membrane potential (depolarization). However, this did not correlate with toxicity. In this study we perform a similar analysis using fluorescent CdTe quantum dots, adapting our tools to make use of the particles fluorescence. We find that two Gram positive strains show direct electron transfer to CdTe, resulting in changes in CdTe fluorescence lifetimes. These two strains also show changes in membrane potential upon nanoparticle binding. Two Gram negative strains do not show these effects - nevertheless, they are over 10-fold more sensitive to CdTe than the Gram positives. We find subtoxic levels of Cd{sup 2+} release from the particles upon irradiation of the particles, but significant production of hydroxyl radicals, suggesting that the latter is a major source of toxicity. These results help establish mechanisms of toxicity and also provide caveats for use of certain reporter dyes with fluorescent nanoparticles which will be of use to anyone performing these assays. The findings also suggest future avenues of inquiry into electron transfer processes between nanomaterials and bacteria.

  4. Novel synthesis of β-cyclodextrin functionalized CdTe quantum dots as luminescent probes

    NASA Astrophysics Data System (ADS)

    Chen, Xiao-Feng; Zhou, Min; Chang, Yan-Ping; Ren, Cui-Ling; Chen, Hong-Li; Chen, Xing-Guo

    2012-12-01

    A novel, inexpensive procedure for the preparation of highly fluorescent and water-soluble CdTe quantum dots (QDs) using β-cyclodextrin (β-CD) as surface-coating agents was fabricated through the substitution reaction at the C-6 position of mono-6-deoxy-6-(p-tolylsulfonyl)-cyclodextrin (6-TsO-β-CD) by the sbnd NH2 of (3-aminopropyl)triethoxysilane-coated CdTe QDs (APTES/CdTe QDs) under mild conditions. X-ray powder diffraction (XRD), Fourier transform infrared spectra (FT-IR), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), ultraviolet and visible (UV-vis) spectrophotometer, and fluorescence (FL) spectrophotometer were used to characterize the obtained nanoparticles, which proved that the CdTe QDs have been effectively modified by β-CD. The quantum yields (QYs) of CdTe QDs, APTES/CdTe QDs and β-CD/APTES/CdTe QDs in water comparative to Rhodamine 6G were about 17%, 12%, and 9%, respectively. A pair of isomer o,p'-DDT and p,p'-DDT was chosen as the template molecules to evaluate the molecular recognition properties of β-CD/APTES/CdTe QDs. The results revealed that β-CD/APTES/CdTe QDs simultaneously possessed unique optical properties of QDs and excellent molecules recognition ability of β-CD through combining their individual distinct advantages.

  5. Capture kinetics at deep-level defects in MBE-grown CdTe layers

    NASA Astrophysics Data System (ADS)

    Olender, Karolina; Wosinski, Tadeusz; Makosa, Andrzej; Kret, Slawomir; Kolkovsky, Valery; Karczewski, Grzegorz

    2011-04-01

    The results of deep-level transient spectroscopy (DLTS) investigations in n-type CdTe layers grown by the molecular-beam epitaxy (MBE) technique on lattice-mismatched GaAs substrates are described. Three electron traps and one hole trap, at rather low concentrations of the order of 1013 cm-3, have been revealed in the DLTS spectra measured under various bias conditions of Schottky diodes prepared on the as-grown CdTe layers. One of the electron traps has been attributed to electron states of dislocations on the ground of the logarithmic capture kinetics for capture of electrons into the trap states. The other three traps, displaying exponential capture kinetics, have been attributed to native point defects produced during the epitaxial growth of CdTe. The microscopic nature of the defects responsible for the traps is discussed taking into account recent results of first-principles calculations of the properties of dominant native defects in CdTe.

  6. Investigation of deep level defects in CdTe thin films

    SciTech Connect

    Shankar, H.; Castaldini, A.; Dauksta, E.; Medvid, A.; Cavallini, A.

    2014-02-21

    In the past few years, a large body of work has been dedicated to CdTe thin film semiconductors, as the electronic and optical properties of CdTe nanostructures make them desirable for photovoltaic applications. The performance of semiconductor devices is greatly influenced by the deep levels. Knowledge of parameters of deep levels present in as-grown materials and the identification of their origin is the key factor in the development of photovoltaic device performance. Photo Induced Current Transient Spectroscopy technique (PICTS) has proven to be a very powerful method for the study of deep levels enabling us to identify the type of traps, their activation energy and apparent capture cross section. In the present work, we report the effect of growth parameters and LASER irradiation intensity on the photo-electric and transport properties of CdTe thin films prepared by Close-Space Sublimation method using SiC electrical heating element. CdTe thin films were grown at three different source temperatures (630, 650 and 700 °C). The grown films were irradiated with Nd:YAG LASER and characterized by Photo-Induced Current Transient Spectroscopy, Photocurrent measurementand Current Voltage measurements. The defect levels are found to be significantly influenced by the growth temperature.

  7. 14%-efficient flexible CdTe solar cells on ultra-thin glass substrates

    SciTech Connect

    Rance, W. L.; Burst, J. M.; Reese, M. O.; Gessert, T. A.; Metzger, W. K.; Barnes, T. M.; Meysing, D. M.; Wolden, C. A.; Garner, S.; Cimo, P.

    2014-04-07

    Flexible glass enables high-temperature, roll-to-roll processing of superstrate devices with higher photocurrents than flexible polymer foils because of its higher optical transmission. Using flexible glass in our high-temperature CdTe process, we achieved a certified record conversion efficiency of 14.05% for a flexible CdTe solar cell. Little has been reported on the flexibility of CdTe devices, so we investigated the effects of three different static bending conditions on device performance. We observed a consistent trend of increased short-circuit current and fill factor, whereas the open-circuit voltage consistently dropped. The quantum efficiency under the same static bend condition showed no change in the response. After storage in a flexed state for 24 h, there was very little change in device efficiency relative to its unflexed state. This indicates that flexible glass is a suitable replacement for rigid glass substrates, and that CdTe solar cells can tolerate bending without a decrease in device performance.

  8. Long carrier lifetimes in large-grain polycrystalline CdTe without CdCl2

    NASA Astrophysics Data System (ADS)

    Jensen, S. A.; Burst, J. M.; Duenow, J. N.; Guthrey, H. L.; Moseley, J.; Moutinho, H. R.; Johnston, S. W.; Kanevce, A.; Al-Jassim, M. M.; Metzger, W. K.

    2016-06-01

    For decades, polycrystalline CdTe thin films for solar applications have been restricted to grain sizes of microns or less whereas other semiconductors such as silicon and perovskites have produced devices with grains ranging from less than a micron to more than 1 mm. Because the lifetimes in as-deposited polycrystalline CdTe films are typically limited to less than a few hundred picoseconds, a CdCl2 treatment is generally used to improve the lifetime; but this treatment may limit the achievable hole density by compensation. Here, we establish methods to produce CdTe films with grain sizes ranging from hundreds of nanometers to several hundred microns by close-spaced sublimation at industrial manufacturing growth rates. Two-photon excitation photoluminescence spectroscopy shows a positive correlation of lifetime with grain size. Large-grain, as-deposited CdTe exhibits lifetimes exceeding 10 ns without Cl, S, O, or Cu. This uncompensated material allows dopants such as P to achieve a hole density of 1016 cm-3, which is an order of magnitude higher than standard CdCl2-treated devices, without compromising the lifetime.

  9. Characterization of Highly Efficient CdTe Thin Film Solar Cells by Low-Temperature Photoluminescence

    NASA Astrophysics Data System (ADS)

    Okamoto, Tamotsu; Matsuzaki, Yuichi; Amin, Nowshad; Yamada, Akira; Konagai, Makoto

    1998-07-01

    Highly efficient CdTe thin film solar cells prepared by close-spaced sublimation (CSS) method with a glass/ITO/CdS/CdTe/Cu-doped carbon/Ag structure were characterized by low-temperature photoluminescence (PL) measurement. A broad 1.42 eV band probably due to VCd Cl defect complexes appeared as a result of CdCl2 treatment. CdS/CdTe junction PL revealed that a CdSxTe1-x mixed crystal layer was formed at the CdS/CdTe interface region during the deposition of CdTe by CSS and that CdCl2 treatment promoted the formation of the mixed crystal layer. Furthermore, in the PL spectra of the heat-treated CdTe after screen printing of the Cu-doped carbon electrode, a neutral-acceptor bound exciton (ACu0, X) line at 1.590 eV was observed, suggesting that Cu atoms were incorporated into CdTe as effective acceptors after the heat treatment.

  10. Static atomic displacements in a CdTe epitaxial layer on a GaAs substrate

    NASA Astrophysics Data System (ADS)

    Horning, R. D.; Staudenmann, J.-L.

    1987-05-01

    A (001)CdTe epitaxial layer on a (001)GaAs substrate was studied by x-ray diffraction between 10 and 360 K. The CdTe growth took place at 380 °C in a vertical gas flow metalorganic chemical vapor deposition reactor. Lattice parameters and integrated intensities of both the substrate and the epitaxial layer using the (00l) and (hhh) Bragg reflections reveal three important features. Firstly, the GaAs substrate does not exhibit severe strain after deposition and it is as perfect as a bulk GaAs. Secondly, the CdTe unit cell distorts tetragonally with a⊥>a∥ below 300 K. The decay of the (00l) reflection intensities as a function of the temperature yields a Debye temperature of 142 K, the same value as for bulk CdTe. Thirdly, a temperature-dependent isotropic static displacement of the Cd and the Te atoms is introduced to account for the anomalous behavior of the (hhh) intensities.

  11. The role of substrate surface alteration in the fabrication of vertically aligned CdTe nanowires.

    PubMed

    Neretina, S; Hughes, R A; Devenyi, G A; Sochinskii, N V; Preston, J S; Mascher, P

    2008-05-01

    Previously we have described the deposition of vertically aligned wurtzite CdTe nanowires derived from an unusual catalytically driven growth mode. This growth mode could only proceed when the surface of the substrate was corrupted with an alcohol layer, although the role of the corruption was not fully understood. Here, we present a study detailing the remarkable role that this substrate surface alteration plays in the development of CdTe nanowires; it dramatically improves the size uniformity and largely eliminates lateral growth. These effects are demonstrated to arise from the altered surface's ability to limit Ostwald ripening of the catalytic seed material and by providing a surface unable to promote the epitaxial relationship needed to sustain a lateral growth mode. The axial growth of the CdTe nanowires is found to be exclusively driven through the direct impingement of adatoms onto the catalytic seeds leading to a self-limiting wire height associated with the sublimation of material from the sidewall facets. The work presented furthers the development of the mechanisms needed to promote high quality substrate-based vertically aligned CdTe nanowires. With our present understanding of the growth mechanism being a combination of selective area epitaxy and a catalytically driven vapour-liquid-solid growth mode, these results also raise the intriguing possibility of employing this growth mode in other material systems in an effort to produce superior nanowires.

  12. Nanoscale Imaging of Band Gap and Defects in Polycrystalline CdTe Photovoltaic Devices

    NASA Astrophysics Data System (ADS)

    Zhitenev, Nikolai; Yoon, Yohan; Chae, Jungseok; Katzenmeyer, Aaron; Yoon, Heayoung; An, Sangmin; Shumacher, Joshua; Centrone, Andrea

    To further increase the power efficiency of polycrystalline thin film photovoltaic (PV) technology, a detailed understanding of microstructural properties of the devices is required. In this work, we investigate the microstructure of CdTe PV devices using two optical spectroscopies. Sub-micron thickness lamella samples were cut out from a PV device, either in cross-section or in-plane, by focused ion beam. The first technique is the photothermal induced resonance (PTIR) used to obtain absorption spectra over a broad range of wavelengths. In PTIR, a wavelength tunable pulsed laser is combined with an atomic force microscope to detect the local thermal expansion of lamella CdTe sample induced by light absorption. The second technique based on a near-field scanning optical microscope maps the local absorption at fixed near-IR wavelengths with energies at or below CdTe band-gap energy. The variation of the band gap throughout the CdTe absorber determined from PTIR spectra is ~ 20 meV. Both techniques detect strong spatial variation of shallow defects over different grains. The spatial distribution of mid-gap defects appears to be more uniform. The resolution, the sensitivity and the applicability of these two approaches are compared.

  13. X-RAY PHOTOEMISSION ANALYSIS OF PASSIVATED Cd(1-x)ZnxTe SURFACES FOR IMPROVED RADIATION DETECTORS

    SciTech Connect

    Nelson, A; Conway, A; Reinhardt, C; Ferreira, J; Nikolic, R; Payne, S

    2008-05-12

    Surface passivation of device-grade CdZnTe was investigated using x-ray photoelectron spectroscopy in combination with transport property measurements after Br-MeOH (2% Br) and KOH/NH{sub 4}F/H{sub 2}O{sub 2} solutions were used to etch and oxidize the surface. High-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for radiation detector devices.

  14. Development of a low-noise, 4th-order readout ASIC for CdZnTe detectors in gamma spectrometer applications

    NASA Astrophysics Data System (ADS)

    Wang, Jia; Su, Lin; Wei, Xiaomin; Zheng, Ran; Hu, Yann

    2016-09-01

    This paper presents an ASIC readout circuit development, which aims to achieve low noise. In order to compensate the leakage current and improve gain, a dual-stage CSA has been utilized. A 4th-order high-linearity shaper is proposed to obtain a Semi-Gaussian wave and further decrease the noise induced by the leakage current. The ASIC has been designed and fabricated in a standard commercial 2P4M 0.35 μm CMOS process. Die area of one channel is about 1190 μm×147 μm. The input charge range is 1.8 fC. The peaking time can be adjusted from 1 μs to 3 μs. Measured ENC is about 55e- (rms) at input capacitor of 0 F. The gain is 271 mV/fC at the peaking time of 1 μs.

  15. Material properties limiting the performance of CZT gamma-ray detectors

    SciTech Connect

    Bolotnikov,A.E.; Babalola, S.; Camarda, G. S.; Cui, Y.; Egarievwe, S. U.; Hossain, A.; Yang, G.; James, R. B.

    2009-03-16

    CdZnTe (CZT) nuclear radiation detectors are advanced sensors that utilize innovative technologies developed for wide band-gap semiconductor industry and microelectronics. They open opportunities for new types of room-temperature operating, field deployable instruments that provide accurate identification of potential radiological threats and timely awareness for both the civilian and military communities. Room-temperature radiation detectors are an emerging technology that relies on the use of high-quality CZT crystals whose availability is currently limited by material non-uniformities and the presence of extended defects. To address these issues, which are most critical to CZT sensor developments, we developed X-ray mapping and IR transmission microscopy systems to characterize both CZT crystals and devices. Since a customized system is required for such X-ray measurements, we use synchrotron radiation beams available at BNL's National Synchrotron Light Source. A highly-collimated and high-intensity X-ray beam supports measurements of areas as small as 10 x 10 {micro}m{sup 2}, and allowed us to see fluctuations in collected charge over the entire area of the detector in a reasonable time. The IR microscopy system allows for 3D visualization of Te inclusions and other extended defects. In this paper, we describe the experimental techniques used in our measurements and typical results obtained from CZT samples produced by different suppliers.

  16. Synthesis and optical characterization of nanocrystalline CdTe thin films

    NASA Astrophysics Data System (ADS)

    Al-Ghamdi, A. A.; Khan, Shamshad A.; Nagat, A.; Abd El-Sadek, M. S.

    2010-11-01

    From several years the study of binary compounds has been intensified in order to find new materials for solar photocells. The development of thin film solar cells is an active area of research at this time. Much attention has been paid to the development of low cost, high efficiency thin film solar cells. CdTe is one of the suitable candidates for the production of thin film solar cells due to its ideal band gap, high absorption coefficient. The present work deals with thickness dependent study of CdTe thin films. Nanocrystalline CdTe bulk powder was synthesized by wet chemical route at pH≈11.2 using cadmium chloride and potassium telluride as starting materials. The product sample was characterized by transmission electron microscope, X-ray diffraction and scanning electron microscope. The structural characteristics studied by X-ray diffraction showed that the films are polycrystalline in nature. CdTe thin films with thickness 40, 60, 80 and 100 nm were prepared on glass substrates by using thermal evaporation onto glass substrate under a vacuum of 10 -6 Torr. The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary part of dielectric constant) of CdTe thin films was studied as a function of photon energy in the wavelength region 400-2000 nm. Analysis of the optical absorption data shows that the rule of direct transitions predominates. It has been found that the absorption coefficient, refractive index ( n) and extinction coefficient ( k) decreases while the values of optical band gap increase with an increase in thickness from 40 to 100 nm, which can be explained qualitatively by a thickness dependence of the grain size through decrease in grain boundary barrier height with grain size.

  17. Hardware simulator of Caliste-SO detectors for STIX instrument

    NASA Astrophysics Data System (ADS)

    Podgórski, P.; Ścisłowski, D.; Kowaliński, M.; Mrozek, T.; Steślicki, M.; Barylak, J.; Barylak, A.; Sylwester, J.; Krucker, S.; Hurford, G. J.; Arnold, N. G.; Orleański, P.; Meuris, A.; Limousin, O.; Gevin, O.; Grimm, O.; Etesi, L.; Hochmuth, N.; Battaglia, M.; Csillaghy, A.; Kienreich, I. W.; Veronig, A.; Bloomfield, D. Shaun; Byrne, M.; Massone, A. M.; Piana, M.; Giordano, S.; Skup, K. R.; Graczyk, R.; Michalska, M.; Nowosielski, W.; Cichocki, A.; Mosdorf, M.

    2013-10-01

    The Spectrometer Telescope for Imaging X-rays (STIX) is one of 10 instruments on-board Solar Orbiter mission of the European Space Agency (ESA) scheduled to be launched in 2017. STIX is aimed to provide imaging spectroscopy of solar thermal and non-thermal hard X-ray emissions from 4 keV to 150 keV using a Fourier-imaging technique. The instrument employs a set of tungsten grids in front of 32 pixelized CdTe detectors. These detectors are source of data collected and analyzed in real time by Instrument Data Processing Unit (IDPU). In order to support development and implementation of on-board algorithms a dedicated detector hardware simulator is designed and manufactured as a part of Electrical Ground Support Equipment (EGSE) for STIX instrument. Complementary to the hardware simulator is data analysis software which is used to generate input data and to analyze output data. The simulator will allow sending strictly defined data from all detectors' pixels at the input of the IDPU for further analysis of instrument response. Particular emphasis is given here to the simulator hardware design.

  18. Development of an ASIC for Si/CdTe detectors in a radioactive substance visualizing system

    NASA Astrophysics Data System (ADS)

    Harayama, Atsushi; Takeda, Shin`ichiro; Sato, Goro; Ikeda, Hirokazu; Watanabe, Shin; Takahashi, Tadayuki

    2014-11-01

    We report on the recent development of a 64-channel analog front-end ASIC for a new gamma-ray imaging system designed to visualize radioactive substances. The imaging system employs a novel Compton camera which consists of silicon (Si) and cadmium telluride (CdTe) detectors. The ASIC is intended for the readout of pixel/pad detectors utilizing Si/CdTe as detector materials, and covers a dynamic range up to 1.4 MeV. The readout chip consists of 64 identical signal channels and was implemented with X-FAB 0.35 μm CMOS technology. Each channel contains a charge-sensitive amplifier, a pole-zero cancellation circuit, a low-pass filter, a comparator, and a sample-hold circuit, along with a Wilkinson-type A-to-D converter. We observed an equivalent noise charge of ~500 e- and a noise slope of ~5 e-/pF (r.m.s.) with a power consumption of 2.1 mW per channel. The chip works well when connected to Schottky CdTe diodes, and delivers spectra with good energy resolution, such as ~12 keV (FWHM) at 662 keV and ~24 keV (FWHM) at 1.33 MeV.

  19. First-principles study of back-contact effects on CdTe thin-film solar cells

    NASA Astrophysics Data System (ADS)

    Du, Mao-Hua

    2009-11-01

    Forming a chemically stable low-resistance back contact for CdTe thin-film solar cells is critically important to the cell performance. This paper reports theoretical study of the effects of the back-contact material, Sb2Te3 , on the performance of the CdTe solar cells. First-principles calculations show that Sb impurities in p -type CdTe are donors and can diffuse with low diffusion barrier. There properties are clearly detrimental to the solar-cell performance. The Sb segregation into the grain boundaries may be required to explain the good efficiencies for the CdTe solar cells with Sb2Te3 back contacts.

  20. Modeling Cu Migration in CdTe Solar Cells Under Device-Processing and Long-Term Stability Conditions: Preprint

    SciTech Connect

    Teeter, G.; Asher, S.

    2008-05-01

    An impurity migration model for systems with material interfaces is applied to Cu migration in CdTe solar cells. In the model, diffusion fluxes are calculated from the Cu chemical potential gradient. Inputs to the model include Cu diffusivities, solubilities, and segregation enthalpies in CdTe, CdS and contact materials. The model yields transient and equilibrium Cu distributions in CdTe devices during device processing and under field-deployed conditions. Preliminary results for Cu migration in CdTe photovoltaic devices using available diffusivity and solubility data from the literature show that Cu segregates in the CdS, a phenomenon that is commonly observed in devices after back-contact processing and/or stress conditions.

  1. Modeling Cu Migration in CdTe Solar Cells Under Device-Processing and Long-Term Stability Conditions (Poster)

    SciTech Connect

    Teeter, G.; Asher, S.

    2008-05-01

    An impurity migration model for systems with material interfaces is applied to Cu migration in CdTe solar cells. In the model, diffusion fluxes are calculated from the Cu chemical potential gradient. Inputs to the model include Cu diffusivities, solubilities, and segregation enthalpies in CdTe, CdS and contact materials. The model yields transient and equilibrium Cu distributions in CdTe devices during device processing and under field-deployed conditions. Preliminary results for Cu migration in CdTe PV devices using available diffusivity and solubility data from the literature show that Cu segregates in the CdS, a phenomenon that is commonly observed in devices after back-contact processing and/or stress conditions.

  2. One-Dimensional Reaction-Diffusion Simulation of Cu Migration in Polycrystalline CdTe Solar Cells

    SciTech Connect

    Guo, Da; Akis, Richard; Brinkman, Daniel; Sankin, Igor; Fang, Tian; Vasileska, Dragica; Ringhofer, Christain

    2014-06-13

    In this work, we report on developing 1D reaction-diffusion solver to understand the kinetics of p-type doping formation in CdTe absorbers and to shine some light on underlying causes of metastabilities observed in CdTe PV devices. Evolution of intrinsic and Cu-related defects in CdTe solar cell has been studied in time-space domain self-consistently with free carrier transport and Poisson equation. Resulting device performance was simulated as a function of Cu diffusion anneal time showing pronounced effect the evolution of associated acceptor and donor states can cause on device characteristics. Although 1D simulation has intrinsic limitations when applied to poly-crystalline films, the results suggest strong potential of the approach in better understanding of the performance and metastabilities of CdTe photovoltaic device.

  3. Magnetron sputtering based direct fabrication of three dimensional CdTe hierarchical nanotrees exhibiting stable superhydrophobic property

    NASA Astrophysics Data System (ADS)

    Luo, Bingwei; Deng, Yuan; Wang, Yao; Shi, Yongming; Cao, Lili; Zhu, Wei

    2013-09-01

    Three dimensional CdTe hierarchical nanotrees are initially prepared by a simple one-step magnetron sputtering method without any templates or additives. The CdTe hierarchical nanotrees are constructed by the spear-like vertical trunks and horizontal branches with the diameters of about 100 nm at bottom and became cuspidal on the top. The particular nanostructure imparts these materials superhydrophobic property, and this property can be preserved after placing in air for 90 days, and is stable even after the ultraviolet light and X-ray irradiation, respectively. This study provides a simple strategy to achieve superhydrophobic properties for CdTe materials at lower temperature, which opens a new potential for CdTe solar cell with self-cleaning property.

  4. Growth of CdTe on Si(100) surface by ionized cluster beam technique: Experimental and molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Araghi, Houshang; Zabihi, Zabiholah; Nayebi, Payman; Ehsani, Mohammad Mahdi

    2016-10-01

    II-VI semiconductor CdTe was grown on the Si(100) substrate surface by the ionized cluster beam (ICB) technique. In the ICB method, when vapors of solid materials such as CdTe were ejected through a nozzle of a heated crucible into a vacuum region, nanoclusters were created by an adiabatic expansion phenomenon. The clusters thus obtained were partially ionized by electron bombardment and then accelerated onto the silicon substrate at 473 K by high potentials. The cluster size was determined using a retarding field energy analyzer. The results of X-ray diffraction measurements indicate the cubic zinc blende (ZB) crystalline structure of the CdTe thin film on the silicon substrate. The CdTe thin film prepared by the ICB method had high crystalline quality. The microscopic processes involved in the ICB deposition technique, such as impact and coalescence processes, have been studied in detail by molecular dynamics (MD) simulation.

  5. A facile and green preparation of high-quality CdTe semiconductor nanocrystals at room temperature

    NASA Astrophysics Data System (ADS)

    Liu, Yan; Shen, Qihui; Yu, Dongdong; Shi, Weiguang; Li, Jixue; Zhou, Jianguang; Liu, Xiaoyang

    2008-06-01

    One chemical reagent, hydrazine hydrate, was discovered to accelerate the growth of semiconductor nanocrystals (cadmium telluride) instead of additional energy, which was applied to the synthesis of high-quality CdTe nanocrystals at room temperature and ambient conditions within several hours. Under this mild condition the mercapto stabilizers were not destroyed, and they guaranteed CdTe nanocrystal particle sizes with narrow and uniform distribution over the largest possible range. The CdTe nanocrystals (photoluminescence emission range of 530-660 nm) synthesized in this way had very good spectral properties; for instance, they showed high photoluminescence quantum yield of up to 60%. Furthermore, we have succeeded in detecting the living Borrelia burgdorferi of Lyme disease by its photoluminescence image using CdTe nanocrystals.

  6. Coexistence of optically active radial and axial CdTe insertions in single ZnTe nanowire.

    PubMed

    Wojnar, P; Płachta, J; Zaleszczyk, W; Kret, S; Sanchez, Ana M; Rudniewski, R; Raczkowska, K; Szymura, M; Karczewski, G; Baczewski, L T; Pietruczik, A; Wojtowicz, T; Kossut, J

    2016-03-14

    We report on the growth, cathodoluminescence and micro-photoluminescence of individual radial and axial CdTe insertions in ZnTe nanowires. In particular, the cathodoluminescence technique is used to determine the position of each emitting object inside the nanowire. It is demonstrated that depending on the CdTe deposition temperature, one can obtain an emission either from axial CdTe insertions only, or from both, radial and axial heterostructures, simultaneously. At 350 °C CdTe grows only axially, whereas at 310 °C and 290 °C, there is also significant deposition on the nanowire sidewalls resulting in radial core/shell heterostructures. The presence of Cd atoms on the sidewalls is confirmed by energy dispersive X-ray spectroscopy. Micro-photoluminescence study reveals a strong linear polarization of the emission from both types of heterostructures in the direction along the nanowire axis.

  7. Influence of Kilo-Electron Oxygen Ion Irradiation on Structural, Electrical and Optical Properties of CdTe Thin Films

    NASA Astrophysics Data System (ADS)

    Honey, Shehla; Thema, F. T.; Bhatti, M. T.; Ishaq, A.; Naseem, Shahzad; Maaza, M.

    2016-09-01

    In this paper, effect of oxygen (O+) ion irradiation on the properties of polycrystalline cubic structure CdTe thin films has been investigated. CdTe thin films were irradiated with O+ ions of energy 80keV at different fluence ranging from 1×1015 to 5×1016 ion/cm2 at room temperature. At 1×1015 ion/cm2 O+ ions fluence, the CdTe structure was maintained while XRD peaks of cubic phase were shifted toward lower angles. At 5×1016 ion/cm2 O+ ions fluence, cubic structure of CdTe thin films was transformed into hexagonal structure. In addition, electrical resistivity and optical bandgap were decreased with increasing O+ ion beam irradiation.

  8. A new method for charge-loss correction of room-temperature semiconductor detectors using digital trapezoidal pulse shaping

    NASA Astrophysics Data System (ADS)

    Nakhostin, M.; Veeramani, P.

    2012-06-01

    It is well known that semiconductor detectors operating at room temperature can be read out at high rate, with good noise performance and low sensitivity to ballistic deficit, by using trapezoidal (flat-topped) pulse shaping. Nevertheless, the energy resolution of these detectors is also affected by chargetrapping inside the detector crystal, which can not be compensated by the standard trapezoidal pulse shaping. A new digital algorithm based on trapezoidal pulse shaping, to compensate for the charge-trapping effect while minimizing the electronic noise, has been developed. The application of the pulse processing algorithm to a 5 × 5 × 1 mm3 planar Schottky CdTe detector leads to an energy resolution of 1.15% FWHM at 662 keV at room temperature, which is considerably superior to the results of the standard pulse filters.

  9. Process Development for High Voc CdTe Solar Cells: Phase I, Annual Technical Report, October 2005 - September 2006

    SciTech Connect

    Ferekides, C. S.; Morel, D. L.

    2007-04-01

    The focus of this project is the open-circuit voltage of the CdTe thin-film solar cell. CdTe continues to be one of the leading materials for large-scale cost-effective production of photovoltaics, but the efficiency of the CdTe solar cell has been stagnant for the last few years. At the manufacturing front, the CdTe technology is fast paced and moving forward with U.S.-based First Solar LLC leading the world in CdTe module production. To support the industry efforts and continue the advancement of this technology, it will be necessary to continue improvements in solar cell efficiency. A closer look at the state-of-the-art performance levels puts the three solar cell efficiency parameters of short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF) in the 24-26 mA/cm2, 844?850 mV, and 74%-76% ranges respectively. During the late 1090s, efforts to improve cell efficiency were primarily concerned with increasing JSC, simply by using thinner CdS window layers to enhance the blue response (<510 nm) of the CdTe cell. These efforts led to underscoring the important role 'buffers' (or high-resistivity transparent films) play in CdTe cells. The use of transparent bi-layers (low-p/high-p) as the front contact is becoming a 'standard' feature of the CdTe cell.

  10. Correlations of Capacitance-Voltage Hysteresis with Thin-Film CdTe Solar Cell Performance During Accelerated Lifetime Testing

    SciTech Connect

    Albin, D.; del Cueto, J.

    2011-03-01

    In this paper we present the correlation of CdTe solar cell performance with capacitance-voltage hysteresis, defined presently as the difference in capacitance measured at zero-volt bias when collecting such data with different pre-measurement bias conditions. These correlations were obtained on CdTe cells stressed under conditions of 1-sun illumination, open-circuit bias, and an acceleration temperature of approximately 100 degrees C.

  11. Evaluation of toxic effects of CdTe quantum dots on the reproductive system in adult male mice.

    PubMed

    Li, Xiaohui; Yang, Xiangrong; Yuwen, Lihui; Yang, Wenjing; Weng, Lixing; Teng, Zhaogang; Wang, Lianhui

    2016-07-01

    Fluorescent quantum dots (QDs) are highly promising nanomaterials for various biological and biomedical applications because of their unique optical properties, such as robust photostability, strong photoluminescence, and size-tunable fluorescence. Several studies have reported the in vivo toxicity of QDs, but their effects on the male reproduction system have not been examined. In this study, we investigated the reproductive toxicity of cadmium telluride (CdTe) QDs at a high dose of 2.0 nmol per mouse and a low dose of 0.2 nmol per mouse. Body weight measurements demonstrated there was no overt toxicity for both dose at day 90 after exposure, but the high dose CdTe affected body weight up to 15 days after exposure. CdTe QDs accumulated in the testes and damaged the tissue structure for both doses on day 90. Meanwhile, either of two CdTe QDs treatments did not significantly affect the quantity of sperm, but the high dose CdTe significantly decreased the quality of sperm on day 60. The serum levels of three major sex hormones were also perturbed by CdTe QDs treatment. However, the pregnancy rate and delivery success of female mice that mated with the treated male mice did not differ from those mated with untreated male mice. These results suggest that CdTe QDs can cause testes toxicity in a dose-dependent manner. The low dose of CdTe QDs is relatively safe for the reproductive system of male mice. Our preliminary result enables better understanding of the reproductive toxicity induced by cadmium-containing QDs and provides insight into the safe use of these nanoparticles in biological and environmental systems.

  12. Solution-Processed, Ultrathin Solar Cells from CdCl3(-)-Capped CdTe Nanocrystals: The Multiple Roles of CdCl3(-) Ligands.

    PubMed

    Zhang, Hao; Kurley, J Matthew; Russell, Jake C; Jang, Jaeyoung; Talapin, Dmitri V

    2016-06-22

    Solution-processed CdTe solar cells using CdTe nanocrystal (NC) ink may offer an economically viable route for large-scale manufacturing. Here we design a new CdCl3(-)-capped CdTe NC ink by taking advantage of novel surface chemistry. In this ink, CdCl3(-) ligands act as surface ligands, sintering promoters, and dopants. Our solution chemistry allows obtaining very thin continuous layers of high-quality CdTe which is challenging for traditional vapor transport methods. Using benign solvents, in air, and without additional CdCl2 treatment, we obtain a well-sintered CdTe absorber layer from the new ink and demonstrate thin-film solar cells with power conversion efficiency over 10%, a record efficiency for sub-400 nm thick CdTe absorber layer. PMID:27269672

  13. Solid-state photon-counting hybrid detector array for high-resolution multi-energy X-ray imaging

    NASA Astrophysics Data System (ADS)

    Sia, R.; Kleinfelder, S.; Nagarkar, V. V.

    2011-10-01

    We present in this article the development of a photon-counting, energy-discriminating modular detector based on a pixelated CdZnTe sensor coupled pixel-by-pixel to a novel Digital Pixel Sensor (DPS) readout. The detector is designed for munitions inspection, breast X-ray CT and SPECT/MRI. The current DPS design can also be used to read out other solid-state sensors. The prototype detector is 5.5 mm×5.5 mm in size, and consists of 19×19 pixels on a 250 μm pitch. The DPS is designed in a 0.35 μm process, and every pixel includes a preamplifier, a leakage-current subtraction circuit, an auto-zeroed programmable-gain stage, five comparators, a variable-delay reset circuit and five 16 bit counters. The module is expected to operate at high X-ray fluence exceeding 80 MHz/mm 2, and to improve resolution and contrast in images, while significantly enhancing their signal-to-noise ratio, and assist in identifying material composition via dual-energy imaging. The detector design, fabrication and anticipated performance are discussed.

  14. Detector simulation needs for detector designers

    SciTech Connect

    Hanson, G.G.

    1987-11-01

    Computer simulation of the components of SSC detectors and of the complete detectors will be very important for the designs of the detectors. The ratio of events from interesting physics to events from background processes is very low, so detailed understanding of detector response to the backgrounds is needed. Any large detector for the SSC will be very complex and expensive and every effort must be made to design detectors which will have excellent performance and will not have to undergo major rebuilding. Some areas in which computer simulation is particularly needed are pattern recognition in tracking detectors and development of shower simulation code which can be trusted as an aid in the design and optimization of calorimeters, including their electron identification performance. Existing codes require too much computer time to be practical and need to be compared with test beam data at energies of several hundred GeV. Computer simulation of the processing of the data, including electronics response to the signals from the detector components, processing of the data by microprocessors on the detector, the trigger, and data acquisition will be required. In this report we discuss the detector simulation needs for detector designers.

  15. Effects of various deposition times and RF powers on CdTe thin film growth using magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Ghorannevis, Z.; Akbarnejad, E.; Ghoranneviss, M.

    2016-09-01

    Cadmium telluride (CdTe) is a p-type II-VI compound semiconductor, which is an active component for producing photovoltaic solar cells in the form of thin films, due to its desirable physical properties. In this study, CdTe film was deposited using the radio frequency (RF) magnetron sputtering system onto a glass substrate. To improve the properties of the CdTe film, effects of two experimental parameters of deposition time and RF power were investigated on the physical properties of the CdTe films. X-ray Diffraction (XRD), atomic force microscopy (AFM) and spectrophotometer were used to study the structural, morphological and optical properties of the CdTe samples grown at different experimental conditions, respectively. Our results suggest that film properties strongly depend on the experimental parameters and by optimizing these parameters, it is possible to tune the desired structural, morphological and optical properties. From XRD data, it is found that increasing the deposition time and RF power leads to increasing the crystallinity as well as the crystal sizes of the grown film, and all the films represent zinc blende cubic structure. Roughness values given from AFM images suggest increasing the roughness of the CdTe films by increasing the RF power and deposition times. Finally, optical investigations reveal increasing the film band gaps by increasing the RF power and the deposition time.

  16. Liver Toxicity of Cadmium Telluride Quantum Dots (CdTe QDs) Due to Oxidative Stress in Vitro and in Vivo

    PubMed Central

    Zhang, Ting; Hu, Yuanyuan; Tang, Meng; Kong, Lu; Ying, Jiali; Wu, Tianshu; Xue, Yuying; Pu, Yuepu

    2015-01-01

    With the applications of quantum dots (QDs) expanding, many studies have described the potential adverse effects of QDs, yet little attention has been paid to potential toxicity of QDs in the liver. The aim of this study was to investigate the effects of cadmium telluride (CdTe) QDs in mice and murine hepatoma cells alpha mouse liver 12 (AML 12). CdTe QDs administration significantly increased the level of lipid peroxides marker malondialdehyde (MDA) in the livers of treated mice. Furthermore, CdTe QDs caused cytotoxicity in AML 12 cells in a dose- and time-dependent manner, which was likely mediated through the generation of reactive oxygen species (ROS) and the induction of apoptosis. An increase in ROS generation with a concomitant increase in the gene expression of the tumor suppressor gene p53, the pro-apoptotic gene Bcl-2 and a decrease in the anti-apoptosis gene Bax, suggested that a mitochondria mediated pathway was involved in CdTe QDs’ induced apoptosis. Finally, we showed that NF-E2-related factor 2 (Nrf2) deficiency blocked induced oxidative stress to protect cells from injury induced by CdTe QDs. These findings provide insights into the regulatory mechanisms involved in the activation of Nrf2 signaling that confers protection against CdTe QDs-induced apoptosis in hepatocytes. PMID:26404244

  17. High performance SWIR HgCdTe detector arrays

    NASA Astrophysics Data System (ADS)

    Bubulac, L. O.; Tennant, W. E.; Pasko, J. G.; Kozlowski, L. J.; Zandian, M.; Motamedi, M. E.; de Wames, R. E.; Bajaj, J.; Nayar, N.; McLevige, W. V.; Gluck, N. S.; Melendes, R.; Cooper, D. E.; Edwall, D. D.; Arias, J. M.; Hall, R.; D'Souza, A. I.

    1997-06-01

    Short wave infrared (SWIR) devices have been fabricated using Rockwell’s double layer planar heterostructure (DLPH) architecture with arsenic-ion implanted junctions. Molecular beam epitaxially grown HgCdTe/CdZnTe multilayer structures allowed the thin, tailored device geometries (typical active layer thickness was ˜3.5 µm and cap layer thickness was ˜0.4 µm) to be grown. A planar-mesa geometry that preserved the passivation advantages of the DLPH structure with enhanced optical collection improved the performance. Test detectors showed Band 7 detectors performing near the radiative limit (˜3-5X below theory). Band 5 detector performance was ˜4-50X lower than radiative limited performance, apparently due to Shockley-Hall-Read recombination. We have fabricated SWIR HgCdTe 256 × 12 × 2 arrays of 45 um × 45 µm detector on 45 µm × 60 µm centers and with cutoff wavelength which allows coverage of the Landsat Band 5 (1.5-1.75 µm) and Landsat Band 7 (2.08-2.35 µm) spectral regions. The hybridizable arrays have four subarrays, each having a different detector architecture. One of the Band 7 hybrids has demonstrated performance approaching the radiative theoretical limit for temperatures from 250 to 295K, consistent with test results. D* performance at 250K of the best subarray was high, with an operability of ˜99% at 1012 cm Hz1/2/W at a few mV bias. We have observed 1/f noise below 8E-17 AHz 1/2 at 1 Hz. Also for Band 7 test structures, Ge thin film diffractive microlenses fabricated directly on the back side of the CdZnTe substrate showed the ability to increase the effective collection area of small (nominally <20 µm µm) planar-mesa diodes to the microlens size of 48 urn. Using microlenses allows array performance to exceed 1-D theory up to a factor of 5.

  18. Spiral silicon drift detectors

    SciTech Connect

    Rehak, P.; Gatti, E.; Longoni, A.; Sampietro, M.; Holl, P.; Lutz, G.; Kemmer, J.; Prechtel, U.; Ziemann, T.

    1988-01-01

    An advanced large area silicon photodiode (and x-ray detector), called Spiral Drift Detector, was designed, produced and tested. The Spiral Detector belongs to the family of silicon drift detectors and is an improvement of the well known Cylindrical Drift Detector. In both detectors, signal electrons created in silicon by fast charged particles or photons are drifting toward a practically point-like collection anode. The capacitance of the anode is therefore kept at the minimum (0.1pF). The concentric rings of the cylindrical detector are replaced by a continuous spiral in the new detector. The spiral geometry detector design leads to a decrease of the detector leakage current. In the spiral detector all electrons generated at the silicon-silicon oxide interface are collected on a guard sink rather than contributing to the detector leakage current. The decrease of the leakage current reduces the parallel noise of the detector. This decrease of the leakage current and the very small capacities of the detector anode with a capacitively matched preamplifier may improve the energy resolution of Spiral Drift Detectors operating at room temperature down to about 50 electrons rms. This resolution is in the range attainable at present only by cooled semiconductor detectors. 5 refs., 10 figs.

  19. CdTe quantum dots with daunorubicin induce apoptosis of multidrug-resistant human hepatoma HepG2/ADM cells: in vitro and in vivo evaluation

    NASA Astrophysics Data System (ADS)

    Zhang, Gen; Shi, Lixin; Selke, Matthias; Wang, Xuemei

    2011-06-01

    Cadmium telluride quantum dots (Cdte QDs) have received significant attention in biomedical research because of their potential in disease diagnosis and drug delivery. In this study, we have investigated the interaction mechanism and synergistic effect of 3-mercaptopropionic acid-capped Cdte QDs with the anti-cancer drug daunorubicin (DNR) on the induction of apoptosis using drug-resistant human hepatoma HepG2/ADM cells. Electrochemical assay revealed that Cdte QDs readily facilitated the uptake of the DNR into HepG2/ADM cells. Apoptotic staining, DNA fragmentation, and flow cytometry analysis further demonstrated that compared with Cdte QDs or DNR treatment alone, the apoptosis rate increased after the treatment of Cdte QDs together with DNR in HepG2/ADM cells. We observed that Cdte QDs treatment could reduce the effect of P-glycoprotein while the treatment of Cdte QDs together with DNR can clearly activate apoptosis-related caspases protein expression in HepG2/ADM cells. Moreover, our in vivo study indicated that the treatment of Cdte QDs together with DNR effectively inhibited the human hepatoma HepG2/ADM nude mice tumor growth. The increased cell apoptosis rate was closely correlated with the enhanced inhibition of tumor growth in the studied animals. Thus, Cdte QDs combined with DNR may serve as a possible alternative for targeted therapeutic approaches for some cancer treatments.

  20. MBE HgCdTe heterostructure detectors

    NASA Technical Reports Server (NTRS)

    Schulman, Joel N.; Wu, Owen K.

    1990-01-01

    HgCdTe has been the mainstay for medium (3 to 5 micron) and long (10 to 14 micron) wavelength infrared detectors in recent years. Conventional growth and processing techniques are continuing to improve the material. However, the additional ability to tailor composition and placement of doped layers on the tens of angstroms scale using molecular beam epitaxy (MBE) provides the opportunity for new device physics and concepts to be utilized. MBE-based device structures to be discussed here can be grouped into two categories: tailored conventional structures and quantum structures. The tailored conventional structures are improvements on familiar devices, but make use of the ability to create layers of varying composition, and thus band gap, at will. The heterostructure junction can be positioned independently of doping p-n junctions. This allows the small band gap region in which the absorption occurs to be separated from a larger band gap region in which the electric field is large and where unwanted tunneling can occur. Data from hybrid MBE/liquid phase epitaxy (LPE)/bulk structures are given. Quantum structures include the HgTe-CdTe superlattice, in which the band gap and transport can be controlled by alternating thin layers (tens of angstroms thick) of HgTe and CdTe. The superlattice has been shown to exhibit behavior which is non-alloy like, including very high hole mobilities, two-dimensional structure in the absorption coefficient, resonant tunneling, and anisotropic transport.

  1. Imaging, Detection, and Identification Algorithms for Position-Sensitive Gamma-Ray Detectors

    NASA Astrophysics Data System (ADS)

    Wahl, Christopher G.

    Three-dimensional-position-sensitive semiconductors record both the locations and energies of gamma-ray interactions with high resolution, enabling spectroscopy and imaging of gamma-ray-emitting materials. Imaging enables the detection of point sources of gamma rays in an otherwise extended-source background, even when the background spectrum is unknown and may share the point source's spectrum. The generalized likelihood ratio test (GLRT) and source-intensity test (SIT) are applied to this situation to detect one-or-more unshielded point sources from a library of isotopes in a spectrally unknown or known background when the background intensity varies spatially by a factor of two or less. In addition to estimating the number of sources present, their activities, isotopes, and directions from the detector are estimated. Experimental and some simulated results are presented for a single detector and an 18-detector array of 2 cm by 2 cm by 1.5 cm CdZnTe crystals and compared with the performance of spectral-only detection when the background and source are assumed to be spectrally different. Furthermore, the expected detection performance of the 18-detector array system is investigated statistically using experimental data in the case where the background is distinct spectrally from the point source and the possible source location and isotopic identity are known. Including imaging gave at least 7% higher SNR compared to ignoring the image dimension. Also, imaging methods based on the maximum-likelihood, expectation-maximization method are introduced to determine the spatial distribution of isotopes and to find the activity distributions within targets moving with known motion through a radioactive background. Software has also been developed to support the analysis of the data from 3D-position-sensitive spectroscopic systems, for a range of detector designs and applications. The software design and unique features that allow fast multidimensional data analysis are

  2. Effect of surface preparation on the 77 K photoluminescence of CdTe

    NASA Astrophysics Data System (ADS)

    Myers, T. H.; Schetzina, J. F.; Edwards, S. T.; Schreiner, A. F.

    1983-07-01

    Photoluminescence spectra were obtained at 77 K for three undoped CdTe single crystal specimens whose surfaces were prepared by mechanical, conventional chemimechanical, and modified hydroplane polishing techniques, respectively. The hydroplane polished sample was found to be a much brighter source of photoluminescence than either of the other two specimens. In addition, hydroplane polishing produced a photoluminescence spectrum in which nearly all of the emission occurred in a band centered at 1.58 eV rather than in the well-known defect band at 1.42 eV. We interpret these results as providing evidence that hydroplane polishing of CdTe produces a surface having a low density of defects.

  3. High efficiency solution processed sintered CdTe nanocrystal solar cells: the role of interfaces.

    PubMed

    Panthani, Matthew G; Kurley, J Matthew; Crisp, Ryan W; Dietz, Travis C; Ezzyat, Taha; Luther, Joseph M; Talapin, Dmitri V

    2014-02-12

    Solution processing of photovoltaic semiconducting layers offers the potential for drastic cost reduction through improved materials utilization and high device throughput. One compelling solution-based processing strategy utilizes semiconductor layers produced by sintering nanocrystals into large-grain semiconductors at relatively low temperatures. Using n-ZnO/p-CdTe as a model system, we fabricate sintered CdTe nanocrystal solar cells processed at 350 °C with power conversion efficiencies (PCE) as high as 12.3%. JSC of over 25 mA cm(-2) are achieved, which are comparable or higher than those achieved using traditional, close-space sublimated CdTe. We find that the VOC can be substantially increased by applying forward bias for short periods of time. Capacitance measurements as well as intensity- and temperature-dependent analysis indicate that the increased VOC is likely due to relaxation of an energetic barrier at the ITO/CdTe interface.

  4. Effects of Stoichiometry in Undoped CdTe Heteroepilayers on Si

    SciTech Connect

    Gessert, Timothy A.; Colegrove, Eric; Stafford, Brian; Gao, Wei; Sivananthan, Siva; Kuciauskas, Darius; Moutinho, Helio; Farrell, Stuart; Barnes, Teresa

    2015-06-14

    Crystalline CdTe layers have been grown heteroepitaxially onto crystalline Si substrates to establish material parameters needed for advanced photovoltaic (PV) device development and related simulation. These studies suggest that additional availability of the intrinsic anion (i.e., Te) during molecular beam epitaxy deposition can improve structural and optoelectronic quality of the epilayer and the interface between Si substrate and the epilayer. This is seen most notably for thin CdTe epitaxial films (<; ~10 micrometers). Although these observations are foundationally important, they are also relevant to envisioned high-performance multijunction II-VI alloy PV devices-where thin layers will be required to achieve production costs aligned with market constraints.

  5. Diffusion-Reaction Modeling of Cu Migration in CdTe Solar Devices

    SciTech Connect

    Guo, Da; Brinkman, Daniel; Fang, Tian; Akis, Richard; Sankin, Igor; Vasileska, Dragica; Ringhofer, Christian

    2015-09-04

    In this work, we report on development of one-dimensional (1D) finite-difference and two-dimensional (2D) finite-element diffusion-reaction simulators to investigate mechanisms behind Cu-related metastabilities observed in CdTe solar cells [1]. The evolution of CdTe solar cells performance has been studied as a function of stress time in response to the evolution of associated acceptor and donor states. To achieve such capability, the simu-lators solve reaction-diffusion equations for the defect states in time-space domain self-consistently with the free carrier transport. Re-sults of 1-D and 2-D simulations have been compared to verify the accuracy of solutions.

  6. Investigation of the origin of deep levels in CdTe doped with Bi

    SciTech Connect

    Saucedo, E.; Franc, J.; Elhadidy, H.; Horodysky, P.; Ruiz, C. M.; Bermudez, V.; Sochinskii, N. V.

    2008-05-01

    Combining optical (low temperature photoluminescence), electrical (thermoelectric effect spectroscopy), and structural (synchrotron X-ray powder diffraction) methods, the defect structure of CdTe doped with Bi was studied in crystals with dopant concentration in the range of 10{sup 17}-10{sup 19} at./cm{sup 3}. The semi-insulating state observed in crystals with low Bi concentration is assigned to the formation of a shallow donor level and a deep donor recombination center. Studying the evolution of lattice parameter with temperature, we postulate that the deep center is formed by a Te-Te dimer and their formation is explained by a tetrahedral to octahedral distortion, due to the introduction of Bi in the CdTe lattice. We also shows that this model agrees with the electrical, optical, and transport charge properties of the samples.

  7. Fabrication of fluorescent composite with ultrafast aqueous synthesized high luminescent CdTe quantum dots

    SciTech Connect

    Zhang, Lei Chen, Haibin E-mail: mejswu@ust.hk; Wu, Jingshen E-mail: mejswu@ust.hk; Bi, Xianghong

    2014-05-15

    Without precursor preparation, inert gas protection and enormous amount of additives and reductants, CdTe quantum dots (QDs) can be rapidly synthesized with high quality. A 600 nm photoluminescence peak wavelength could be obtained within 1 hour's refluxing through minimal addition of 1,2-diaminoethane (DAE). The theoretical design for the experiments are illustrated and further proved by the characterization results with different concentrations and reagents. On the other hand, generation of CdTe QDs was found even under room temperature by applying droplet quantity of DAE. This indicates that QDs can be synthesized with simply a bottle and no enormous additives required. The QDs were mixed into the epoxy matrix through solution casting method with cetyltrimethylammonium (CTA) capping for phase transfer. The acquired epoxy based nanocomposite exhibits good transparency, compatibility and fluorescence.

  8. Photoluminescence Imaging of Large-Grain CdTe for Grain Boundary Characterization

    SciTech Connect

    Johnston, Steve; Allende Motz, Alyssa; Reese, Matthew O.; Burst, James M.; Metzger, Wyatt K.

    2015-06-14

    In this work, we use photoluminescence (PL) imaging to characterize CdTe grain boundary recombination. We use a silicon megapixel camera and green (532 nm) laser diodes for excitation. A microscope objective lens system is used for high spatial resolution and a field of view down to 190 um x 190 um. PL images of large-grain (5 to 50 um) CdTe samples show grain boundary and grain interior features that vary with processing conditions. PL images of samples in the as-deposited state show distinct dark grain boundaries that suggest high excess carrier recombination. A CdCl2 treatment leads to PL images with very little distinction at the grain boundaries, which illustrates the grain boundary passivation properties. Other process conditions are also shown, along with comparisons of PL images to high spatial resolution time-resolved PL carrier lifetime maps.

  9. CdTe surface roughness by Raman spectroscopy using the 830 nm wavelength.

    PubMed

    Frausto-Reyes, C; Molina-Contreras, J Rafael; Medina-Gutiérrez, C; Calixto, Sergio

    2006-09-01

    A Raman spectroscopic study was performed to detect the surface roughness of a cadmium telluride (CdTe) wafer sample, using the 514.5, 632.8 and 830.0 nm excitations wavelengths. To verify the relation between the roughness and the structure of Raman spectra, in certain zones of the sample, we measured their roughness with an atomic force microscopy. It was found that, using the 830 nm wavelength there is a direct correspondence between the spectrum structure and the surface roughness. For the others wavelengths it was found, however, that there is not a clearly correspondence between them. Our results suggest that, using the excitation wavelength of 830 nm the Raman spectroscopy can be used as an on-line roughness monitor on the CdTe growth.

  10. Identification of critical stacking faults in thin-film CdTe solar cells

    SciTech Connect

    Yoo, Su-Hyun; Walsh, Aron; Butler, Keith T.; Soon, Aloysius; Abbas, Ali; Walls, John M.

    2014-08-11

    Cadmium telluride (CdTe) is a p-type semiconductor used in thin-film solar cells. To achieve high light-to-electricity conversion, annealing in the presence of CdCl{sub 2} is essential, but the underlying mechanism is still under debate. Recent evidence suggests that a reduction in the high density of stacking faults in the CdTe grains is a key process that occurs during the chemical treatment. A range of stacking faults, including intrinsic, extrinsic, and twin boundary, are computationally investigated to identify the extended defects that limit performance. The low-energy faults are found to be electrically benign, while a number of higher energy faults, consistent with atomic-resolution micrographs, are predicted to be hole traps with fluctuations in the local electrostatic potential. It is expected that stacking faults will also be important for other thin-film photovoltaic technologies.

  11. Growth and optical properties of CdTe quantum dots in ZnTe nanowires

    SciTech Connect

    Wojnar, Piotr; Janik, Elzbieta; Baczewski, Lech T.; Kret, Slawomir; Karczewski, G.; Wojtowicz, Tomasz

    2011-09-12

    We report on the formation of optically active CdTe quantum dots in ZnTe nanowires. The CdTe/ZnTe nanostructures have been grown by a gold nanocatalyst assisted molecular beam epitaxy in a vapor-liquid solid growth process. The presence of CdTe insertions in ZnTe nanowire results in the appearance of a strong photoluminescence band in the 2.0 eV-2.25 eV energy range. Spatially resolved photoluminescence measurements reveal that this broad emission consists of several sharp lines with the spectral width of about 2 meV. The large degree of linear polarization of these individual emission lines confirms their nanowire origin, whereas the zero-dimensional confinement is proved by photon correlation spectroscopy.

  12. Structural phase transition of CdTe: an ab initio study.

    PubMed

    Alptekin, Sebahaddin

    2013-01-01

    A constant pressure ab initio MD technique and density functional theory with a generalized gradient approximation (GGA) was used to study the pressure-induced phase transition in zinc-blende CdTe. We found that CdTe undergoes a structural first-order phase transition to [Formula: see text] (binary β-tin) tetragonal structure in the constant pressure molecular dynamics simulation at 20 GPa. When the pressure was increased to 50 GPa, the phase of tetragonal structure converted to a new Imm2 orthorhombic structure. These phase transformations were also calculated by using the enthalpy calculations. Transition phases, lattice parameters and bulk properties we attained are comparable with experimental and theoretical data.

  13. Room temperature ferromagnetism in Co defused CdTe nanocrystalline thin films

    SciTech Connect

    Rao, N. Madhusudhana; Kaleemulla, S.; Begam, M. Rigana

    2014-04-24

    Nanocrystalline Co defused CdTe thin films were prepared using electron beam evaporation technique by depositing CdTe/Co/CdTe stacked layers with different Co thickness onto glass substrate at 373 K followed by annealing at 573K for 2 hrs. Structural, morphological and magnetic properties of of all the Co defused CdTe thin films has been investigated. XRD pattern of all the films exhibited zinc blende structure with <111> preferential orientation without changing the crystal structure of the films. The grain size of the films increased from 31.5 nm to 48.1 nm with the increase of Co layer thickness from 25nm to 100nm. The morphological studies showed that uniform texture of the films and the presence of Co was confirmed by EDAX. Room temperature magnetization curves indicated an improved ferromagnetic behavior in the films with increase of the Co thickness.

  14. Redetermination of Ba(2)CdTe(3) from single-crystal X-ray data.

    PubMed

    Yang, Min; Xia, Sheng-Qing; Tao, Xu-Tang

    2012-10-01

    The previous structure determination of the title compound, dibarium tritelluridocadmate, was based on powder X-ray diffraction data [Wang & DiSalvo (1999 ▶). J. Solid State Chem.148, 464-467]. In the current redetermination from single-crystal X-ray data, all atoms were refined with anisotropic displacement parameters. The previous structure report is generally confirmed, but with some differences in bond lengths. Ba(2)CdTe(3) is isotypic with Ba(2)MX(3) (M = Mn, Cd; X = S, Se) and features (1) (∞)[CdTe(2/2)Te(2/1)](4-) chains of corner-sharing CdTe(4) tetra-hedra running parallel [010]. The two Ba(2+) cations are located between the chains, both within distorted monocapped trigonal-prismatic coordination polyhedra. All atoms in the structure are located on a mirror plane.

  15. CdTe quantum dot as a fluorescence probe for vitamin B12 in dosage form

    NASA Astrophysics Data System (ADS)

    Vaishnavi, E.; Renganathan, R.

    2013-11-01

    We here report the CdTe quantum dot (CdTe QDs)-based sensor for probing vitamin B12 derivatives in aqueous solution. In this paper, simple and sensitive fluorescence quenching measurements has been employed. The Stern-Volmer constant (KSV), quenching rate constant (kq) and binding constant (K) were rationalized from fluorescence quenching measurement. Furthermore, the fluorescence resonance energy transfer (FRET) mechanism was discussed. This method was applicable over the concentration ranging from 1 to 14 μg/mL (VB12) with correlation coefficient of 0.993. The limit of detection (LOD) of VB12 was found to be 0.15 μg/mL. Moreover, the present approach opens a simple pathway for developing cost-effective, sensitive and selective QD-based fluorescence sensors/probes for biologically significant VB12 in pharmaceutical sample with mean recoveries in the range of 100-102.1%.

  16. Hot electron extraction from CdTe quantum dots via beta carotene molecular energy levels

    NASA Astrophysics Data System (ADS)

    Pazhanivel, T.; Nataraj, D.; Devarajan, V. P.; Senthil, K.; Seol, M.; Yong, K.

    2012-06-01

    We report our findings related to hot electron extraction from CdTe quantum dots, and we were able to do this by using beta carotene as an electron acceptor. Transient absorption spectra with two slow recovering negative bleaches at the absorption maximum of the molecule and quantum dot have indicated the slowing down of cooling process and the existence of hot carriers in this hybrid system.

  17. Cyclodextrin capped CdTe quantum dots as versatile fluorescence sensors for nitrophenol isomers

    NASA Astrophysics Data System (ADS)

    Zhang, Zhixing; Zhou, Jie; Liu, Yun; Tang, Jian; Tang, Weihua

    2015-11-01

    Cyclodextrin (CD) capped CdTe quantum dots (QDs) were prepared with uniform dimension (average diameter ~5 nm) and high quantum yield (ca. 65%). By taking advantage of the inclusion complexation of CD, β-CD-CdTe QDs exhibited strong fluorescence quenching in a linear relationship with the concentration of o-, m- and p-nitrophenol in the range of 20-100 μM. The detection limit reached 0.05 μM for o-/p-nitrophenol and 0.3 μM for m-nitrophenol. The fluorescence decay study revealed the stabilization effect of CD covering on CdTe QDs and fine-tuning of the fluorescence for selective ultrasensitive detection of nitrophenol isomers.Cyclodextrin (CD) capped CdTe quantum dots (QDs) were prepared with uniform dimension (average diameter ~5 nm) and high quantum yield (ca. 65%). By taking advantage of the inclusion complexation of CD, β-CD-CdTe QDs exhibited strong fluorescence quenching in a linear relationship with the concentration of o-, m- and p-nitrophenol in the range of 20-100 μM. The detection limit reached 0.05 μM for o-/p-nitrophenol and 0.3 μM for m-nitrophenol. The fluorescence decay study revealed the stabilization effect of CD covering on CdTe QDs and fine-tuning of the fluorescence for selective ultrasensitive detection of nitrophenol isomers. Electronic supplementary information (ESI) available: Experimental procedure and characterization for new materials. See DOI: 10.1039/c5nr06073g

  18. Advanced Research Deposition System (ARDS) for processing CdTe solar cells

    NASA Astrophysics Data System (ADS)

    Barricklow, Keegan Corey

    CdTe solar cells have been commercialized at the Gigawatt/year level. The development of volume manufacturing processes for next generation CdTe photovoltaics (PV) with higher efficiencies requires research systems with flexibility, scalability, repeatability and automation. The Advanced Research Deposition Systems (ARDS) developed by the Materials Engineering Laboratory (MEL) provides such a platform for the investigation of materials and manufacturing processes necessary to produce the next generation of CdTe PV. Limited by previous research systems, the ARDS was developed to provide process and hardware flexibility, accommodating advanced processing techniques, and capable of producing device quality films. The ARDS is a unique, in-line process tool with nine processing stations. The system was designed, built and assembled at the Materials Engineering Laboratory. Final assembly, startup, characterization and process development are the focus of this research. Many technical challenges encountered during the startup of the ARDS were addressed in this research. In this study, several hardware modifications needed for the reliable operation of the ARDS were designed, constructed and successfully incorporated into the ARDS. The effect of process condition on film properties for each process step was quantified. Process development to achieve 12% efficient baseline solar cell required investigation of discrete processing steps, troubleshooting process variation, and developing performance correlations. Subsequent to this research, many advances have been demonstrated with the ARDS. The ARDS consistently produces devices of 12% +/-.5% by the process of record (POR). The champion cell produced to date utilizing the ARDS has an efficiency of 16.2% on low cost commercial sodalime glass and utilizes advanced films. The ARDS has enabled investigation of advanced concepts for processing CdTe devices including, Plasma Cleaning, Plasma Enhanced Closed Space Sublimation

  19. Characteristics of metal/sputtered CdTe/ n-GaAs diode structures

    NASA Astrophysics Data System (ADS)

    Das, M. B.; Krishnaswamy, S. V.; Petkie, R.; Elmuradi, M.

    1983-02-01

    Incorporation of a thin layer of r.f. sputtered CdTe between the metal and n-GaAs, has resulted in diode structures with MIS and Schottky barrier types C/V characteristics and low-current forward and reverse I/V characteristics. These structures have the potential to be useful in improving the performance of GaAs FET's for microwave and high speed applications.

  20. Advanced UV Detectors and Detector Arrays

    NASA Technical Reports Server (NTRS)

    Pankove, Jacques I.; Torvik, John

    1998-01-01

    Gallium Nitride (GaN) with its wide energy bandgap of 3.4 eV holds excellent promise for solar blind UV detectors. We have successfully designed, fabricated and tested GaN p-i-n detectors and detector arrays. The detectors have a peak responsivity of 0.14A/W at 363 nm (3.42 eV) at room temperature. This corresponds to an internal quantum efficiency of 56%. The responsivity decreases by several orders of magnitude to 0.008 A/W at 400 nm (3.10 eV) giving the excellent visible rejection ratio needed for solar-blind applications.