Stoichiometric Effects on the Photoelectric Properties of LiInSe₂ Crystals for Neutron Detection

⁶LiInSe₂ is a promising semiconductor candidate for thermal neutron detection due to its large capture cross-section. However, the charge collection efficiency is still insufficient for high resolution for the grown-in defects induced by the stoichiometric deviation. In this work, we report photoelectric properties of stoichiometric LiInSe₂ crystal boules up to 70 mm in length and 20 mm in diameter grown by the vertical Bridgman method. Inductively coupled plasma measurements demonstrate that the ratio of Li, In, and Se of the as-grown crystal is very close to 1:1:2, which is optimized by low temperature synthesis processing. The obtained single crystals display high bulk resistivity in the range of 10¹¹-10¹² Ω·cm and a direct band gap of 2.01-2.83 eV with a changeable color from red to yellow. The electronic structure of LiInSe₂ was studied using first-principles density functional theory calculations, which predicts that the antisite defects of In_Li and Li_In are the dominant factor for the different crystal colors observed. The stoichiometric LiInSe₂ crystal gives an improved energy resolution, for a semiconductor detector when illuminated with a ²⁴¹Am@5.48 MeV α source, of 23.3%. The electron mobility-lifetime product (μτ) is ∼2.5 × 10^-5 cm² V^-1.