Defect absorption in selenium films by photothermal deflection spectroscopy

Sub-gap absorption spectra of selenium films are investigated by photothermal deflection spectroscopy. The selenium films are prepared by vacuum evaporation of selenium pellets. Raman spectroscopy reveals that as-deposited films are amorphous, and the films annealed at 100 °C are trigonal crystal. Photothermal deflection spectroscopy is extended to infrared light of 0.31 eV with maintaining high sensitivity, and detects weak absorption at energies below the band gap. Five absorption peaks and tail absorption are observed in selenium films, and the absorption peak energies are 1.32, 1.08, 0.47, 0.41 and 0.34 eV, respectively. These absorption tail and peaks are derived from selenium, and the origin of these absorptions is explained based on the oxygen impurity and the defect structure of the selenium film.