R5A  Alternative Materials 1

Friday, Nov. 6  08:30-10:05  California

Session Chair:  Ernesto Dieguez, PROFESSOR, Spain

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(08:30) R5A-1, invited, New SiPM Technologies for Low Power, Low Cost, and High Resolution Detectors

E. Marsden, C. Duff, A. Tuff, A. Bell, I. Radley

Kromek, Sedgefield, UK
We report a number of studies on the integration of silicon photomultiplier (SiPM) technologies with current and emerging commercial gamma and neutron scintillator materials to deliver field deployment requirements for the detection of nuclear materials. A systems analysis approach will be shown based on detailed materials, sensor and electronics characterisation. This approach is critical to enable trade-off decisions to meet overall design goals. Examples will be shown of how this trade-off modeling has resulted in the availability of new detection capabilities. This same systems approach is employed to design new system components to deliver capabilities not available with current technologies. Examples of this approach for new integrated SiPM and ASIC designs will be demonstrated.

(08:50) R5A-2, Gamma Ray Detection with Pb2P2Se6

P. L. Wang1, Z. Liu2, P. Chen2, J. A. Peters2, G. Tan1, J. Im3, W. Lin1, A. J. Freeman3, B. W. Wessels2, M. G. Kanatzidis1

1Chemistry, Northwestern University, Evanston, Illinois, United States
2Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
3Physics and Astronomy, Northwestern University, Evanston, Illinois, United States
The heavy metal selenophosphate, Pb2P2Se6, was investigated as a potential cost-effective X-ray/?-ray detector material. Crystal boules of Pb2P2Se6 up to 40mm in length and 11mm in diameter were grown by a vertical Bridgman method. The obtained crystal ingots were cut and processed into size-appropriate wafers for physical, optical and transport property studies as well as gamma-ray detector testing. The Pb2P2Se6 compound was found to exhibit a congruent melting behavior and robust physical properties. This material is an indirect band gap semiconductor with bandgap of 1.88eV and has electrical resistivity in the range of 1×1010O•cm. The Pb2P2Se6 single crystal sample displayed a significant photo-conductivity response under Ag X-ray. In addition, the Pb2P2Se6 samples generated spectroscopic responses to 57Co ?-ray radiation. The mobility-lifetime product of Pb2P2Se6 is in the range of a (µt)e = 3×10-5 cm2•V-1 for electrons.

(09:05) R5A-3, Optical Properties of Perovskites for Hard Radiation Detection at Room Temperature

S. Kostina, M. Sebastian, K. McCall, C. C. Stoumpos, P. Chen, J. A. Peters, Z. Liu, M. G. Kanatzidis, B. W. Wessels

Northwestern University, Evanston, IL, USA
Semiconducting perovskite compounds have recently attracted much attention due to their remarkable optical and electronic properties. Recently we reported that the Bridgman grown materials were suitable as hard radiation detectors. Here we report our current progress on CsPbX3 (X = Cl, Br) and organo-lead trihalide compounds MAPbY3 (Y=Br, I) to utilize their photo-conversion potential in the field of high energy radiation detection. The compounds exhibit high mobility-lifetime (�t) products on the order of 10^(-4)-10^(-3) cm^2�V^(-1) for both electrons and holes. These compounds have been shown to detect x-ray and gamma ray radiation with well-resolved characteristic peaks. By using photoluminescence spectroscopy, near bandedge luminescence was observed but neither donor-acceptor pair (DAP) nor deep level radiative defects were observed within the gap of the CsPbX3 perovskite compounds. A number of relevant properties such as defect stability were investigated. These results indicate that the Bridgman grown materials should be suitable for hard radiation detector applications due to the absence of radiative deep level defects.

(09:20) R5A-4, Molecular Beam Epitaxy Growth of High Resistivity AlSb for Room Temperature Radiation Detectors

E. I. Vaughan1, S. Addamane2,3, D. Shima2,4, G. Balakrishnan2,3, A. A. Hecht1

1Nuclear Engineering, University of New Mexico, Albuquerque, NM, USA
2Center for High Technology Materials, University of New Mexico, Albuquerque, NM, USA
3Electrical and Computer Engineering, University of New Mexico, Albuquerque, NM, USA
4Nanoscience and Microsystems Engineering, University of New Mexico, Albuquerque, NM, USA
AlSb has been proposed as a very strong candidate for room temperature detectors due to its large band gap Eg, 300K = 1.62 eV, the high atomic number of Sb, and the theorized symmetric electron and hole properties. Symmetric electron and hole properties (µt) will allow for more uniform signal over the crystal, following a more symmetric charge induction efficiency as represented by the Hecht relation. This allows for larger crystal volumes and thus greater detection efficiency for high-energy photons. Being a dual carrier detector also improves statistics and therefore expected resolution over CdZnTe. At issue is how to grow pure and defect free materials to test the theorized properties due to the extremely reactive nature of AlSb; Al oxides rapidly and Sb reacts even with the growth crucibles. We have applied MBE to grow very high quality, potentially detector-grade AlSb material. Using semi-insulating GaAs substrates, 3 microns of AlSb was grown by MBE for preliminary characterization studies. In undoped samples, an average Hall mobility of 1200 cm2/Vs was found, with a Hall carrier concentration of 1010 /cm3 and a resistivity of 106 O cm. Intentionally doped samples were grown using GaTe for n-type and Be for p-type conductivity in the AlSb layer to understand doping concentration effects. Further growth and measurements are being performed, carrier lifetime is being studied, and diodes are being grown by MBE to test the material for radiation response.

(09:35) R5A-5, Enhanced Gamma Ray Sensitivity in Defect Engineered BiI3 Detectors

J. C. Nino1, P. M. Johns1, M. Bliss2, K. Jordan1, J. E. Baciak1

1Materials Science and Engineering, University of Florida, Gainesville, FL, USA
2Radiation Detection & Nuclear Sciences, Pacific Northwest National Lab, Richland, WA, USA
BiI3 is a wide band-gap compound semiconductor with a high effective atomic number that has been anticipated to exhibit higher detection efficiency than other compound semiconductors such as HgI2 and CdZnTe, making it of particular interest for moderate and high energy gamma-ray detection applications. However, until recently the low resistivity of BiI3 resulted in high leakage currents and degradation of the electrical properties thus limiting the detector performance. Here, we will discuss novel defect engineering strategies that successfully mitigate the obstacles associated with iodine vacancies in the material. Specifically, the electrical properties and radiation response of both undoped and Sb-doped BiI3 (Sb:BiI3) single crystals grown via the vertical Bridgman technique will be presented. We will show that Sb incorporation as a dopant effectively limits the formation of iodine vacancies and also strengthens the naturally soft layer compound. Moreover, in this talk we will present the microstructural investigation of Sb:BiI3 that led to the discovery of void inclusions within the crystals. We will show that employing a superheating gradient step during crystal growth effectively reduces the presence of voids, resulting in a significant improvement in the crystal quality. These combined enhancements (defect engineering and growth profile optimization), has yielded superheated Sb:BiI3 crystals with improved electronic properties, enhanced structural integrity, and spectral sensitivity which surpasses nominally grown crystals. For example, polarization effects, which previously limited detector lifetime to below 12 hours, have been suppressed to allow detectors to sense radiation after several days under bias. In addition, Frisch collar and pixelated electrodes have produced detectors that can capture separate signals from 241Am and 153Gd sources, demonstrating for the first time the discrimination of separate gamma ray peaks in a BiI3 spectra.

(09:50) R5A-6, Characterization of Lithium Indium Diselenide

D. S. Hamm1, E. D. Lukosi1, M. R. Rust1, E. H. Herrera1, A. C. Stowe2, B. W. Wiggins2, A. Burger3

1Dept. of Nuclear Engineering, University of Tennessee - Knoxville, Knoxville, TN, United States
2CNS-Y12 National Security Complex, Oak Ridge, TN, United States
3Dept. of Life and Physical Sciences, Fisk University, Nashville, TN, United States
Lithium indium diselenide (6LiInSe2) is single crystalline, semiconducting material under development as a novel, solid-state thermal neutron detector. High thermal neutron detection efficiency is accomplished through enrichment in 6Li, a primary proposed replacement to 3He. Due to the significant thermal neutron absorber density, this semiconductor has a high intrinsic efficiency for slow neutrons. The thermal neutron interaction of lithium-6 has a large Q-value of 4.78 MeV, ideal for neutron-gamma threshold discrimination Characterization of the charge carrier and electrical properties of this material are crucial to its development and application. As a novel detector, little is known about the charge collection properties of this material including drift velocity, charge carrier mobility, trapping time constant, charge collection efficiency, and work function. Furthermore, the development of this material as a detector hinges on the interaction of the semiconductor with metallic contacts used for charge collection. Consequently, determination of contact behavior, Schottky or Ohmic, and subsequent electrical transport properties for a variety of metal contact configurations is required for development. While this novel material is yet to be fully characterized, this study represents a significant step in the development of this material with respect to its thermal neutron detection potential. The scintillation properties of the LiInSe2 crystal would account for a loss of charge at the carrier generation site. Further investigations will determine the correlation between charge collected and scintillation yield at varying biases to test this hypothesis.