STUDY OF THERMOSTIMULATED CHANGES IN THE EDGE ABSORPTION SPECTRUM OF SIOx SUBOXIDE FILMS

In the spectral range of wavelengths λ = 400–750 nm, experimental transmission (T) and reflection (R) spectra of suboxide SiOx films (x » 1.3), deposited on quartz substrates by vacuum evaporation of silicon monoxide, were obtained before and after their annealing in a nitrogen atmosphere over a wide temperature range of 100–1100 °C. The evolution of the absorption spectrum A(λ) = 1-R-T of the studied samples with an increase in the annealing temperature Ta from the substrate temperature during deposition Td = 100 °C to 500 °C consists in its blue shift, and starting from Ta = 600 °C this trend changes to the opposite. The maximum red shift was observed at Ta = 910 °C. After annealing at 1100 °C, the absorption spectrum becomes close to the spectrum of the unannealed film. The maximum relative changes in absorption in the long-wave part of the spectrum can be associated with a decrease in defect absorption, and changes in absorption in the range λ ≈ 480-560 nm ― with a change in the width of the band gap of the film due to annealing. These conclusions are confirmed by the analysis of the absorption coefficient spectra, plotted in Urbach and Tauc coordinates. With an increase in the annealing temperature to 500 °C, there is a twofold decrease in the Urbach energy EU and an increase in the optical (Tauc) bandgap width Ego, which is explained by the structural ordering of the SiO1.3 film. With further growth of Ta up to 1010 °C, the increase of Ego changes to a decrease, while the value of EU changes little. Such behavior of Ego, EU is explained by the formation of amorphous silicon nanoparticles, whose optical bandgap and mobility gap Eg exhibit a size effect. The estimates of the value of Eg for both the SiO1.3 film and amorphous silicon nanoparticles agree well with the values ​​available in the literature, obtained from theoretical calculations. The values ​​of Ego and EU for the film annealed at 1100 °C indicate the appearance of silicon nanocrystallites in it.