Optical properties of amorphous Selenium Thin Films prepared by Thermal Evaporation

Abstract

Selenium thin films were prepared by thermal evaporation on glass slides at a vacuum pressure of 1.9×10-5 Torr. The samples were annealed at temperatures of 373 and 423 K. The optical transmittance (T) and reflectance (R) of the films were recorded between 300 nm and 1000 nm using an Avantes UV Spectrophotometer. The percentage transmittance shows a decrease from 61% for the unannealed Se film to 34% when the film is annealed at 423 K. The extinction coefficient values show a similar trend as the absorption spectral. The skin depth shows a reduction with the increase of annealing temperature. The effect of annealing temperature on the energy band gap was also investigated. Optical energy band gap determined from the absorption coefficient shows a decrease from 2.38 eV for the unannealed sample to 1.98 eV and 1.88 eV when the film is annealed at 373 and 423 K respectively