Scalable Low-Cost Large-Area Micro-Structured Thermal Neutron Detectors

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Abstract

Semiconductor thermal neutron (0.025 eV) detectors with micro-structured cavities backfilled with neutron conversion materials (10B, 6LiF) show a profound increase in the intrinsic thermal neutron detection efficiency as compared to the conventional planar detectors with a thin film neutron conversion layer. In this dissertation, devices utilizing the 10B(n,α) 7Li reaction are studied due to the chemical stability of 10B, relatively high thermal neutron capture cross-section (3840 barns) and high energy (1.4 MeV) of reaction products from thermal neutron capture in 10B. First, planar detectors utilizing thin film CdTe-based p-n junction diodes with a 10B neutron conversion film were investigated. The neutron detection efficiency in planar detectors is limited to <4%, significantly restricting its use in commercial applications. The research and developments discussed in this work include low-cost fabrication of silicon and perovskite-based micro-structured detectors. The neutron detection efficiency of microstructured detectors was initially predicted using Monte-Carlo simulations as a function of microstructure geometry. In micro-structured silicon diodes, a novel conformal doping strategy using enriched 10B powders back-filled in the microstructures where, 10B is shown to act as a source for conformal doping while also providing neutron sensitivity to micro-structured diodes. Silicon microstructures, when conformally doped, were demonstrated to show sig nificant increase in neutron detection efficiency. As a result, in micro-structured silicon detectors, a thermal neutron detection efficiency of 21% is achieved, which is significantly higher than the 3.5% obtained in planar silicon detectors. Finally, the perovskite-based micro-structured detectors utilizing thin film CsPbBr3 was developed. A novel dry etching strategy using HBr+Ar plasma was implemented in this work to obtain microstructures in CsPbBr3. The preliminary results show that an intrinsic efficiency of ∼4.5%, with a high γ/n discrimination of ∼10−7 can be obtained using micro-structured CsPbBr3-based detectors.

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Keywords

Neutron counters, Semiconductor doping, Nanocrystals -- Etching, Semiconductors -- Etching

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