Photosensitivity of 20GeO2 : 80SiO2 hydrogen-loaded and non-hydrogen-loaded thin films

Abstract

Photosensitive materials offer great potential for passive and active optical devices in communication, data manipulation and storage. We prepared photosensitive germanosilicate (20GeO2 : 80SiO2) inorganic thin films by the sol–gel method. These films were annealed at various temperatures in the range of 700–900 °C. The films annealed at 900 °C were found to be fully densified and were porous when annealed below 900 °C. The UV KrF laser (248 nm) has been used to induce refractive index change (Δn). We have studied the Fourier transform infra-red (FTIR) spectroscopy and the refractive index changes of the hydrogen-loaded and as-deposited samples before and after UV illumination. For the porous samples, the −OH absorption band around 3400 cm−1 increases with hydrogen-loading and decreases with UV radiation. The hydrogen-loading has induced absorption around 500–600 cm−1 for all our samples (both porous and dense samples) and that indicates the formation of Si–H bonds. The Si–H absorption bands disappeared after UV illumination. We observed the high Δn of about 0.0094 for the as-deposited dense film annealed at 900 °C and value enhanced to 0.0096 after H2-loading. For our samples, the large induced refractive index change is explained in terms of the formation of the oxygen related defects upon UV exposure. This is related to the induced absorption band around 620–740 cm−1 in the FTIR spectra.