Deposition and characterisation of sulphur doped diamond-like carbon films using pulsed laser deposition method

Abstract

Ablation of a sulphur-graphite target was carried out by ArF excimer laser deposition at a laser wavelength of 193 nm and fluence of 10 and 20 J/cm² in vacuum to produce sulphur-doped diamond-like carbon (S-DLC) films. The sulphur graphite target was made from sulphur and graphite powder mixed at different sulfur molar percentages, e.g. 0%, 1%, 5%, 10% and 25%. S DLC films were deposited on silicon and quartz substrates at different substrate temperatures, e.g. room temperature, 150oC and 250℃. The effects of substrate temperature, laser fluence and sulphur molar percentage on the electrical, optical, mechanical and structural properties of the resulting films were studied. The S-DLC films in this work showed resistivity values in the range of 10³-10⁶ Ω⋅cm, corresponding to a band gap in the range of 0.25 2.00 eV. The carrier concentration was found to be in the range of 10¹⁴ -10¹⁸ cm⁻³. The effect of doping the DLC films with sulphur was found to convert the films into an n-type semiconductor. The Hall mobility was in the range of 10⁻⁵-1 cm²⋅V⁻¹⋅s⁻¹. The thickness of the films was in the hundred nanometers range, while the hardness of the films was in the range of 10-30 GPa. The surface morphology showed the presence of micron-sized particulates on the surface. Elemental composition analysis confirmed the presence of sulphur in the films.