Tuning the band gap of hematite α-Fe₂O₃ by sulfur doping

Based on the density functional theory, the band structure and optical absorption of the isovalent sulfur-doped hematite α-Fe₂O ₃ are studied systematically. The results show that the band gap of α-Fe₂O_{3 - x}S_x decreases monotonically with increasing the sulfur concentration, resulting in an obvious increase of the optical absorption edge in the visible range. Most intriguingly, unlike the pure α-Fe₂O₃ material, the α-Fe ₂O_3-xS_x with x≈0.17 (S concentration of ∼5.6%) exhibits a direct band gap of an ideal value (∼1.45 eV), together with high optical absorption (∼10⁵ cm^-1) and lower carriers effective masses. These results indicate that α-Fe ₂O_{3 - x}S_x, with a proper concentration of sulfur, may serve as a promising candidate for low-cost solar-cell materials.