Role of fluorine in two-dimensional dichalcogenide of SnSe ₂

Authors report an effect of F substitution on layered SnSe₂ through the successful synthesis of polycrystalline SnSe_2-δF _x (0.000 ≤ x ≤ 0.010) by solid-state reaction. Accompanied with density functional theory calculations, the blue shift of A_1g peak in Raman spectra reveal that F^- ions are substituted at Se vacancy sites as decreasing the reduced mass of vibrational mode associated with Sn-Se bonding. From the measurements of electrical parameters, conductivity as well as carrier concentration are governed by thermally activated behavior, while such behavior is suppressed in Hall mobility, which occurs as F ratio increases. Based on Arrhenius relation, it is found that the potential barrier height at the grain boundary is suppressed with increasing F amount, suggesting that the F^- ion is a promising candidate for the grain boundary passivation in the two-dimensional dichalcogenide system.