Thermal Neutron Detection with Lithium-Based Semiconductors

Li-based semiconductor materials represent a promising alternative to 3-He and scintillation materials for thermal neutron detection and imaging instruments. Semiconductor crystals of LiInSe₂, LiInP₂Se₆, and LiGaInSe₂ (LiGa_0.5In_0.5Se₂) were grown using natural and enriched lithium (⁶Li). The materials were characterized for electronic and optical properties including optical transmission, current-voltage (I-V) characteristic for resistivity, and bandgap. Thermal neutron detectors were fabricated and characterized for neutron and gamma-ray response. Pulse height spectra were collected from a moderated custom-designed ²⁴¹AmBe neutron source and a ⁶⁰Co gamma-ray source. The LiInSe₂ samples exhibited a 2.8 eV cutoff in the optical spectrum and a resistivity of ~8×10¹¹ Ω·cm. LiInSe₂ devices exhibit a noise floor of <30 keV which operated at a field of 630 V/mm, for the 0.8-mm thick device. The Vertical Gradient Freeze (VGF) grown LiInP₂Se₆ samples exhibited a 2.2 eV cutoff in the optical spectrum and resistivity of ~4×10¹² Ω·cm. The Chemical Vapor Transport (CVT) grown LiInP₂Se₆ devices exhibit a noise floor of <60 keV which operated at a field of 8,000 V/mm, for the 0.05-mm thick device. Furthermore, the long-term stability of LiInSe₂ devices during multiple weeks under continuous bias was investigated.