Wide-Band Semiconductor Detectors
Neutron Detectors Based on III-Nitride Semiconductors
Tech Area / Field
- PHY-SSP/Solid State Physics/Physics
- INS-DET/Detection Devices/Instrumentation
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Genisaretskaya S V
Karpov Institute of Physical Chemistry (2), Russia, Kaluga reg., Obninsk
- State Research and Design Institute of Rare-Metal Industry, Russia, Moscow
- Bubble Technology Industries Inc., Canada, ON, Chalk River\nChonbuk National University, Korea, Jeonju\nWright State University / Semiconductor Research Center, USA, OH, Dayton\nUniversity of Florida / Department of Materials Science and Engineering, USA, FL, Gainesville
Project summaryIt is the aim of the present project to develop physical and physico-technical foundations of designing group III-nitrides based wide-band detectors of neutrons for dosimetry and spectrometry of neutron sources (nuclear reactors, neutron generators) and for field control and monitoring of neutron emitting isotopes.
Development of compact, reliable, affordable detectors for remote control of neutrons’ spectra, fluence and flux is a very important scientific and technical task. Such detectors are necessary for organizing effective border control to prevent smuggling of fission materials by terrorist groups trying to build self-made nuclear explosive devices. These detectors are also required for the purposes of dosimetry and spectrometry of neutron fluxes in the channels of research nuclear reactors or in neutron generators.
Currently, dosimetry of neutrons is based on various detectors using scintillating effects, on monitoring changes in optical luminescence or absorption or on measurements of neutron irradiation induced α, β, γ or proton activity. Obviously, such devices are poorly suited for the tasks of remote control. At the same time, neutron spectra are generally measured using proportional gas detectors whose window is covered with materials converting neutron fluxes into the fluxes of charged particles (boron and polyethylene are the most common types of these materials). Proportional gas detectors can be used to organize remote control, but these detectors have some inherent drawbacks, the most important among which are large dimensions, fragility, and very high cost. For some time already it has been attempted to use instead of proportional gas detectors solid state detectors based on semiconductor sensors in which boron or polyethylene are deposited close to the active region of devices. ?-particles or protons formed in these B or polyethylene films create ionization pulses in the space charge region of the semiconductor detector, thus allowing to determine the spectrum and flux of the incident neutrons. However, attempts to build such semiconductor detectors using Ge or Si and GaAs were not successful. Ge detectors need cooling below room temperature which is very inconvenient for the applications we have in mind. As for Si or GaAs, for neutron detecting applications, the detector needs to have high density for proton or alpha-particles stopping and good alpha-voltaic energy conversion efficiency so that good sensitivity to neutrons can be achieved. This latter efficiency is directly proportional to the energy bandgap of the semiconductor material. Both factors generally favor wide-bandgap materials with a high density. For GaN the density is several times higher than for Si and rough theoretical estimates suggest that the theoretical efficiency for neutron detection in GaN can be ~27%, higher than for Si and GaAs.
In the course of the present project it is planned to practically test this idea by building and studying characteristics of prototype GaN Schottky diodes or p-i-n detectors with trenches formed by dry etching and filled with boron. Detailed studies will be performed to find out how the deposition of such regions will affect electrical and recombination properties of devices, what will be the changes in detector characteristics as a function of neutron dose and energy, what will be the materials requirements in terms of concentration of dopants, minority carriers lifetimes, and dislocation density in order to attain optimal performance and the highest radiation hardness of detectors. Various materials, such as standard high-dislocation-density MOCVD GaN, low-dislocation-density HVPE GaN, and low-dislocation-density ELOG GaN will be tested. All these materials will be compared in terms of the highest attainable thickness of the space charge region, charge collection efficiency and spectral resolution upon detecting neutrons and α-particles with known spectra. The materials will also be compared in terms of resistance to neutron irradiation. Possibilities of neutron transmutation doping of GaN will be investigated. Detailed modeling of neutron radiation effects in GaN taking into account disordered regions formation alongside the formation of point radiation defects will be performed.
The two groups gathered to participate in this project, the group at the Karpov Institute of Physical Chemistry (2) and the group at the State Institute of Rare Metals have all the necessary experience to successfully achieve the aims of the present work. The distribution of the workload between them will be as follows. Detector characteristics will be studied jointly by both groups. Neutron irradiation, nuclear transmutation doping, studies of detectors performance as remote neutron dosimeters, theoretical modeling of radiation effects taking into account the formation of both point defects and disordered regions in order to predict radiation induced changes in electrical properties, density of electronic states, optical properties of GaN will be carried out at the Karpov Institute of Physical Chemistry (2). The State Institute of Rare Metals group will be responsible for growth of detector structures by HVPE, for the studies of low-dislocation-density ELOG detector material, for experimental studies of neutron irradiation induced changes of electrical and recombination properties and deep traps spectra in various detector materials. Within the framework of this project we also plan to study test detector structures fabricated at the University of Florida (dry etching, formation of trenches, B deposition).
The fact that our two groups have already developed in the course of the work on the previous ICTS project many of the necessary experimental techniques and have acquired a valuable experience in studying the processes of radiation defects formation in group III-nitrides (see some representative references below [1-10]) will definitely be a big advantage when working on the proposed project. Our research will be carried out in close coordination with the laboratory of Prof. S.J. Pearton at the University of Florida who will independently carry out research in the same direction. Prof. Pearton is one of the collaborators in the present project and he has kindly agreed to provide technical assistance in fabrication of detector test structures. Another collaborator who has agreed to provide direct technical assistance is Prof. In-Hwan Lee at the Chonbuk National University in Korea. His group has demonstrated very good results in growth of very high quality ELOG GaN which he will provide in limited amounts for our studies.
All in all, the current project well fits the general aims of ICTS. It will provide alternative employment for a large number (38 people) of physicists and technologists formerly actively occupied in defense oriented work. It will also provide an opportunity for the scientists from different countries to actively collaborate in solving an interesting and vastly important task concerning all civilized nations. Finally, in the course of work on the project the Russian scientists will acquire extremely valuable experience in carrying out research aimed at developing a commercially attractive product. And there is little doubt that, in case of success, all the necessary conditions for creating such a product will be put in place.
- A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, A. V.Markov, S. J. Pearton, N. G. Kolin, D. I. Merkurisov, and V. M. Boiko, Neutron irradiation effects on electrical properties and deep-level spectra in undoped n-AlGaN/GaN heterostructures, J. Appl. Phys. 98, 033529 (2005)
- A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, A.V. Markov, S.J. Pearton, N.G. Kolin, D.I. Merkurisov, V.M. Boiko, C-R. Lee, I-H. Lee, Neutron irradiation effects in undoped n-GaN films, J. Vac. Sci. Technol. B25(2), 436-442 (2007)
- A. Y. Polyakov, N. B. Smirnov, A. V. Govorkov, A. V. Markov, N. G. Kolin, D. I. Merkurisov, V. M. Boiko, K. D. Shcherbatchev, V. T. Bublik, M. I. Voronova, S. J. Pearton, A. Dabiran, and A. V. Osinsky. Neutron irradiation effects in p-GaN. J.Vac. Sci.Technol. B 24,2256 (2006).
- A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, A.V. Markov, N.G. Kolin, D.I. Merkurisov, V.M. Boiko, K.D. Shcherbatchev, V.T. Bublik, M.I. Voronova, I-H. Lee, C.R. Lee, Fermi level pinning in heavily neutron irradiated GaN, J. Appl. Phys. 100(9), 093715-093719 (2006)
- A.V. Govorkov, N.B. Smirnov, A.Y. Polyakov, A.V. Markov, L. Voss, S.J. Pearton, Microcathodoluminescence and electrical properties of GaN epitaxial layers grown on thick freestanding GaN substrates, J. Vac. Sci. Technol. B24(2), 790-794 (2006)
- A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, A.V. Markov, N.G. Kolin, V.M. Boiko, D.I. Merkurisov, S.J. Pearton, Neutron irradiation effects in undoped n-AlGaN, J. Vac. Sci. Technol. B24(3), 1094-1097 (2006)
- E.B. Yakimov, P.S. Vergeles, A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, In-Hwan Lee, Cheul Ro Lee, S.J. Pearton, Spatial variations of doping and lifetime in epitaxial laterally overgrown GaN, Appl. Phys. Lett., 90, 152114 (2007)
- A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, A.V. Markov, E.B. Yakimov, P.S. Vergeles, N.G. Kolin, D.I. Merkurisov, V.M. Boiko, In-Hwan Lee, Cheul-Ro Lee, and S.J. Pearton, Neutron radiation effects in epitaxially laterally overgrown GaN films, J. Electron. Mater. 2007, in press
- A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, Jihyun Kim, F.Ren, G.T.Thaler, R.M. Frazier, B.P. Gila, C.R. Abernathy, S.J. Pearton, I.A. Buyanova, E.J. Rudko, W.M. Chen, C-C. Pan, Y-I Chyi and J.M.Zavada, Electrical and Luminescent Properties and the Spectra of Deep Centers in GaMnN/InGaN Light Emitting Diodes, J. Electron. Mater.33(3), 241-247 (2004)
- In-Hwan Lee, A.Y. Polyakov, N.B. Smirnov, A.V. Govorkov, A.V. Markov, S.J. Pearton, “Electrical and recombination properties and deep traps spectra in MOCVD ELOG GaN layers”, Phys. Stat. Sol. (c), v.3, #6, 2087-2090 (2006)
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