Thermal neutron detector based on hexagonal boron nitride

Hexagonal boron nitride (h-BN) is highly promising for the construction of next generation solid-state thermal neutron detectors due to its very large thermal neutron capture cross-section of 10B isotope. It also possesses outstanding properties as a neutron detector material, including large energy band gap (Eg = 6.5 eV), high resistivity, high breakdown field, and low leakage current density. Epitaxial layers of h-BN have been synthesized by metal organic chemical vapor deposition (MOCVD) on sapphire substrates. The mobility-lifetime (μτ) products of charge carriers have been measured, which is larger than the value for the more established III-nitride family member GaN thin films grown on sapphire. Detectors based on ¬h-BN thin films were fabricated and the nuclear reaction product pulse height spectra were measured. Thermal neutron detectors with metal–semiconductor–metal (MSM) and planar structures were fabricated. The fabricated detectors exhibit very low leakage current density (as low as 10-11 A/cm2) at a bias voltage of 10 V. The nuclear reaction product pulse-height spectra were measured under thermal neutron irradiation produced by a Californium-252 (252Cf) source moderated by a high density polyethylene (HDPE) block. Very narrow individual peaks corresponding to the reaction product energies of  and Li particles as well as the sum peaks have been clearly resolved in the pulse height spectrum for the first time by a B-based direct-conversion semiconductor neutron detector. Furthermore, the pulse height spectra were measured for h-BN detectors with varying layer thicknesses, from which the charge collection efficiency of h-BN detectors was obtained. Our results indicate that the charge collection efficiency of h-BN MSM detectors is very relatively high (nearly 83%) when a moderate bias voltage was applied to the detectors. These detectors have advantages of semiconductor devices including compact size, light weight, ability to integrate with other functional devices, low voltage operation, and low cost.