Stoichiometric effect on the defect states and optical properties of LiInSe₂ single crystals

LiInSe₂ crystals are promising semiconductor materials for neutron detectors due to the large neutron capture cross-sectional area of the specific isotopes (⁶Li) and high charge transport properties. However, the optoelectronic performance fails to reach the expected level due to the difficulty of controlling the crystal defects. Herein, we modulate the stoichiometric ratio to control the type of defects in single LiInSe₂ crystals grown by the vertical Bridgman method. The UV‒vis-NIR transmission results indicate that the band gap of the yellow colored Li_1.01In₁Se₂ sample is close to ~ 2.83 eV at room temperature, and this value is consistent with the theoretical band gap of LiInSe₂ (~ 2.86 eV). Photoluminescence (PL) spectroscopy was used to analyze the defect concentration. The results indicate that the defect types in the yellow Li_1.01In₁Se₂ single crystal are V_Se⁺ and Li_In^2-; these result from the introduction of excess Li and the suppression of the adverse defects in In_Li²⁺ and V_Li^-. These results demonstrate a feasible route for obtaining high-quality yellow ⁶LiInSe₂ crystals and promote the application of ⁶LiInSe₂ neutron detectors.