Effect of deposition time on the optical properties of vanadium pentoxide films grown on porous silicon nanostructure

Vanadium pentoxide (V₂O₅) thin films were grown on porous silicon (PS) layer by electron beam evaporation technique under an oxygen partial pressure. The morphology of the porous surface before and after V₂O₅ deposition for different evaporation times was observed by the Scanning Electron Microscope (SEM). The predicts changes of the chemical composition and bonds at the porous surface have been studied by FTIR and Raman spectroscopies. Photoluminescence (PL) spectroscopy was carried out to study the effect of vanadium pentoxide thickness on the optical properties of V₂O₅/PS nanocomposites. The PL spectrum of PS show a red-shift of 90 nm following the deposition of vanadium pentoxide while a quenching of the PL intensity was observed. Referring to FTIR and Raman results, the origin of this shift can be attributed to the formation of oxidized vanadium elements at PS surface as well as the creation of localized states by V₂O₅ molecules inside the band gap of PS. The wavelength dependence of optical transmittance, reflectance and absorption coefficients were investigated. An increase in the optical band gap from 1.95 to 2.18 eV was obtained due to Moss-Burstein effect as well as the presence of vacancy defects in V₂O₅ film.