Boron Nitride Neutron Detector with the Ability to Detect Both Thermal and Fast Neutrons

This dissertation focuses on the development of a boron nitride (BN) based fast neutron detector (FND) capable of detecting energies up to tens of mega-electron volts (MeV). BN FND is designed to simultaneously detect both thermal and fast neutrons, making it suitable for applications in fission and fusion environments. With its compact size, superior gamma discrimination, low operating voltage, and cost-effective production and maintenance, the BN FND presents a promising opportunity to replace the Helium-3 gas detectors. Additionally, the BN FND demonstrates suitability for use in extreme environments such as high-temperature conditions (well-logging) and harsh environments like outer space. To fabricate the detector, a thick layer of hexagonal boron nitride (h-BN) was grown by metal-organic chemical vapor deposition (MOCVD) and configured into a neutron detector with a metal-semiconductor-metal (MSM) in a lateral direction. The properties of h-BN, including resistivity, mobility-lifetime product, neutron detection, and charge collection efficiency, were studied. The measured mean free paths of fast neutrons in BN, using a bare Cf-252 and AmBe source emitting fast neutrons ranging from 1 – 9 MeV, were determined to be approximately 7.6 cm and 5.2 cm, respectively. Furthermore, the study revealed the presence of turbostratic phase domains in BN (t-10BN), which exhibited a band gap of (5.5 eV), as evidenced by two distinct sets of channel peaks in the pulsed height spectrum (PHS). The effect of metal contacts on the transport properties of highly resistive h-BN was also investigated. Results indicated that for h-BN with a room temperature resistivity as high as 1014 Ω.cm, as-deposited metal contact was not entirely blocking. By modifying the boundary condition at the metal/semiconductor interface, the contact behavior could be determined to be either ohmic or blocking type. This quantitative understanding applies to all ultra-wide bandgap (UWBG) semiconductors with high electrical resistivities. Finally, the h-BN detector has demonstrated its capability for direct fast neutron detection from a bare AmBe neutron source, achieving a high detection efficiency of 2.2% using a stacked-layer device with a total thickness of 1.4 mm. The successful development of BN FND will significantly impact many applications in society, including detecting radioactive activity for public safety and national security, monitoring nuclear reactors for nuclear fuel identification, and contributing to nuclear waste management and reduction.