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Theses

Neutron detectors based on boron nitride and its alloys

Abstract : Neutron detectors play a crucial role in various applications such as homeland security (airports, borders and ports) to control illegal activities involving nuclear materials, nuclear power plants for neutron radiation safety and monitoring, high energy physics and nuclear science. In addition, recent events such as the Fukushima explosion and the polonium poisoning have stimulated interest in the development of small, portable and low-cost solid-state neutron detectors (SSND). To achieve high efficiency in SSND factors such as neutron absorption and charge collection are critical.The general objective of this work is to develop efficient solid-state thermal neutron detectors based on boron containing III-nitride materials such as boron nitride (BN) and boron-gallium nitride (BGaN). Boron in these materials is very important for the detection of thermal neutrons due to the high neutron capture cross section of the isotope boron-10 (10B) and its low sensitivity to gamma radiation. However, the main challenge with boron containing III-N for neutron detection is the quality of the materials. For instance, growth of thick, high quality single crystalline boron-rich BGaN needed for neutron detectors is difficult due to strain-induced degradations such as phase separation and columnar 3D growth. Therefore, we developed an innovative approach consisting of BGaN/GaN superlattices (SLs) with a nominal boron content of 3% in the BGaN layer. These BGaN/GaN SLs materials were used to fabricate metal-semiconductor-metal (MSM) and p-i-n heterojunction devices, which showed significant neutron-induced signal. Even with this approach, it is found that there are several constraints on the boron content, the quality of the material, and the overall thickness, which are key factors for the realization of high-efficiency neutron detectors.By using binary BN (100% boron) epitaxial layers, higher thermal neutron absorption and performance of neutron detectors are expected. Our group has reported for the first time large area 2D layered h-BN films with high crystalline quality on sapphire substrate by metal organic vapor phase epitaxy (MOVPE). These BN films were used to demonstrate high efficiency deep UV photodetectors. In this work, we have grown up to 2.5µm thick natural and 10B enriched BN samples and used them to fabricate MSM based detectors. The advantages of MSM structures are the ability to achieve self-powered operation, similar to that demonstrated for UV photodetectors, and to benefit from internal gain in order to increase the neutron signal.This work also aims to investigate the control of the electrical conductivity of h-BN by in-situ Mg doping for the future realization of p-n based BN neutron detectors. Since a high boron content is highly desirable for neutron detectors, we have further explored experimentally for the first time a new material: boron-rich BAlN alloys.
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Submitted on : Friday, May 13, 2022 - 5:24:56 PM
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  • HAL Id : tel-03667919, version 1

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Adama Mballo. Neutron detectors based on boron nitride and its alloys. Physics [physics]. Université de Lorraine, 2021. English. ⟨NNT : 2021LORR0236⟩. ⟨tel-03667919⟩

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