Optical properties of titanium trisulphide (TiS₃) thin films

Titanium trisulphide thin films have been grown on quartz substrates by sulphuration of electron-beam evaporated Ti layers (d ∼ 300 nm) in a vacuum sealed ampoule in the presence of sulphur powder at 550 °C for different periods of time (1 to 20 h). Thin films were characterized by X-ray diffraction, energy dispersive analyses of X-ray and scanning electron microscopy. Results demonstrate that films are composed by monoclinic titanium trisulphide. Films show n-type conductivity with a relatively high resistivity (ρ ∼ 4 ± 2 Ω·cm) and high values of the Seebeck coefficient (− 600 μV/K) at room temperature. Values of the optical absorption coefficient about α ∼ 10⁵ cm⁻¹, determined from reflectance and transmittance measurements, have been obtained at photon energies hυ > 2 eV. The absorption coefficient dependence on the photon energy in the range of 1.6–3.0 eV hints the existence of a direct transition with an energy gap between 1.35 and 1.50 eV. By comparing these results with those obtained from bulk TiS₃, a direct transition with lower energy is also found which could have been hidden due to the low value of the absorption coefficient in this energy range. - Highlights: ► Thin films of TiS₃ have been obtained by sulphuration of Ti layers. ► Optical properties of TiS₃ thin films have been determined. ► Optical energy gap of TiS₃ has been obtained. ► Optical properties of bulk TiS₃ have been measured and compared with those of films