Controlling band gap and refractive index in dopant-free α-Fe2O3 films

Abstract

Dopant-free hematite (a-Fe2O3) films are formed at a liquid-vapor interface by means of an easy method in order to control the band gap and refractive index of the films. The a-Fe2O3 films after being transferred to a glass substrate are studied for their structural and optical properties. Control over the thickness of the films in the range from 75 to 400 nm and the constituent nanocrystallite size from 3 to 46 nm is achieved by controlling the synthesis parameters. By controlling the film thickness, crystallite size, and crystallinity of dopant-free a-Fe2O3 films, the optical band gap is increased significantly (by ≈ 0.64 eV) from 2.30 to 2.94 eV, along with increase in the refractive index from 1.35 to 2.8. The observed increase in the optical band gap is explained on the basis of change in lattice symmetry (via change in the c/a ratio) of a-Fe2O3 crystallites.