Analyzing UV/Vis/NIR and Photo-Acoustic Spectra: A Note to the Band Gap of TixSi1-xO2

Exact contact-free and non-destructive opto-electrical analysis of thin film and powder materials are necessary for efficient development and improvement of semiconductor devices. Besides the quality of the apparatus, the grade of the mathematical evaluation models is of importance for correct data acquisition. For UV/Vis/NIR spectroscopy, the single-layer model and the double-layer model, taking into account transmission and reflection spectra (with an integrating sphere), have shown excellent results, compared with other measurement techniques. A further comparatively unknown and contact-free optical analysis method is the photo-acoustic spectroscopy (PAS). In the following, it will be shown that both analyzing methods provide comparable band gap energies, using just the spectra or the well-known Tauc plot, respectively, an adequate novel plot for the PAS method. For verification, the band gap energy, E-g, of a silicon powder has been investigated. Then, direct and indirect E(g)s of special TixSi1-xO2 compounds, x = 10%, ... , 50%-prepared with a sophisticated sol-gel procedure-have been analyzed. The results point out that titanium is bound mainly in TiO2 (rutil), with increasing amounts of brookite and anatase in the case of rising x-values. For Ti contents below 10%, the powder tends, reasonably, to behave like a glass substrate.