Electromodulated transmittance of optical transitions in tungsten oxide

Modulation spectroscopy is a well-established method for the study of optical transitions in semiconductors and has been a valuable asset for the verification of theoretical band structure calculations. The most important aspect of this method is its ability to render clear spectral features with no prior assumptions. One modulation technique is electroabsorption, in which the transmittance of a sample is modulated by the application of a time-varying electric field while light is incident on the sample. In this work, a modified form of electroabsorption was investigated in which the electric field was applied at the interface between the sample and a transparent conducting layer. This technique was applied to investigate the optical transitions in tungsten trioxide (WO₃). The resultant spectral features were distinctly localized in energy. Analysis of the experimental spectra was carried out using Aspnes’ third derivative model, and the results were interpreted in terms of theoretical calculations.