Temperature-dependent optical absorption of SrTiO3

The optical absorption edge and near infrared absorption of SrTiO3 were measured at temperatures from 4 to 1703 K. The absorption edge decreases from 3.25 eV at 4K to 1.8 eV at 1703K and is extrapolated to approximately 1.2 eV at the melting point (2350 K). The transmission in the near IR decreases rapidly above 1400K because of free carrier absorption and is about 50% of the room temperature value at 1673 K. The free carriers are generated by thermal excitation of electrons over the band gap and the formation of charged vacancies. The observed temperature-dependent infrared absorption can be well reproduced by a calculation based on simple models for the intrinsic free carrier concentration and the free carrier absorption coefficient. The measured red shift of the optical absorption edge and the rising free carrier absorption strongly narrow the spectral range of transmission and impede radiative heat transport through the crystal. These effects have to be considered in high temperature applications of SrTiO3-based devices, as the number of free carriers rises considerably, and in bulk crystal growth to avoid growth instabilities. Temperature dependent optical absorption edge of SrTiO3, measured, fitted, and extrapolated to the melting point. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim