Realization of highly efficient hexagonal boron nitride neutron detectors

We report the achievement of highly efficient ¹⁰B enriched hexagonal boron nitride (h-¹⁰BN) direct conversion neutron detectors. These detectors were realized from freestanding 4-in. diameter h-¹⁰BN wafers 43 μm in thickness obtained from epitaxy growth and subsequent mechanical separation from sapphire substrates. Both sides of the film were subjected to ohmic contact deposition to form a simple vertical "photoconductor-type" detector. Transport measurements revealed excellent vertical transport properties including high electrical resistivity (>10¹³ Ω cm) and mobility-lifetime (μτ) products. A much larger μτ product for holes compared to that of electrons along the c-axis of h-BN was observed, implying that holes (electrons) behave like majority (minority) carriers in undoped h-BN. Exposure to thermal neutrons from a californium-252 (²⁵²Cf) source moderated by a high density polyethylene moderator reveals that 43 μm h-¹⁰BN detectors possess 51.4% detection efficiency at a bias voltage of 400 V, which is the highest reported efficiency for any semiconductor-based neutron detector. The results point to the possibility of obtaining highly efficient, compact solid-state neutron detectors with high gamma rejection and low manufacturing and maintenance costs.