Selenium modified Te85Ge15 films elaborated by thermal co-evaporation for infrared applications

With the final objective to manufacture micro-sensors for CO2 detection, one of the major issues in the fabrication of infrared channel waveguides, which is the deposition of a core layer with controlled optical properties, was investigated. The paper reports on the effect of introduction of increasing amount of selenium in Te85Ge15 films. The possibility of tuning the optical properties, i.e. transmission domain and refractive index, principally, was demonstrated. 5 μm-thick Te–Ge–Se amorphous films were deposited by thermal co-evaporation, and deposition conditions were chosen in such a way that a constant content in Ge, fixed at 15 at.%, was obtained. The homogeneity as well as the morphological, thermal and optical properties of the as-obtained nominal Te85 − xGe15Sex films were studied. The homogeneity in thickness and composition was very good on a region of about 4 cm in diameter. The vitreous transition temperature lies between 137 °C and 145 °C depending upon the film composition, and the thermal analysis curves of the films containing more than 60% of selenium did not show any crystallization peak. As expected, the replacement of tellurium by selenium in the films led to a displacement of the optical band gap to the near-infrared and a decrease in the film refractive index. To end, the Se-rich Te–Ge–Se thermal co-evaporated films were shown to be suitable for the fabrication of channel waveguides being operational at 4.2 μm and between 13 and 16 μm, opening the door to the fabrication of micro-sensors for CO2 detection.

► The study of selenium modified Te–Ge films elaborated by thermal co-evaporation
► The Te–Ge–Se films are shown to be more thermally stable than Te–Ge ones.
► The film refractive index can be fine-tuned by changing the Se content.
► The Te–Ge–Se films are transparent from 1 to 16 μm.
► The Te–Ge–Se films are promising candidates for the realization of CO2 micro-sensors.