Optical properties of large band gap β-In2S3−3xO3x compounds obtained by physical vapour deposition

Thin films of large band gap β-In2S3−3xO3x compounds have been synthesised by annealing a multilayer structure of indium and sulphur sequentially deposited. X-ray diffraction measurements, electronic microprobe analysis and quantitative X-ray photoelectron analysis have been performed to characterise the samples. The absorption coefficient, determined from transmission and reflexion measurements, shows that the absorption threshold is blue shifted when oxygen is present in In2S3 and the gap increases about 30%. A theoretical modelisation of these compounds, using the known spinel structure Al2MgO4, is reported. The electronic structure has been calculated with the ab initio Tight Binding Linear Muffin Tin Orbitals method. We obtain an enhancement of the gap under lattice compression. Although this trend also appears in the absence of oxygen, the lattice compression is more favourable when oxygen is present.