Compositional and optical properties of SiOx films and (SiOx/SiOy) junctions deposited by HFCVD

In this work, non-stoichiometric silicon oxide (SiOx) films and (SiOx/SiOy) junctions, as-grown and after further annealing, are characterized by different techniques. The SiOx films and (SiOx/SiOy) junctions are obtained by hot filament chemical vapor deposition technique in the range of temperatures from 900 degrees C to 1,150 degrees C. Transmittance spectra of the SiOx films showed a wavelength shift of the absorption edge thus indicating an increase in the optical energy band gap, when the growth temperature decreases; a similar behavior is observed in the (SiOx/SiOy) structures, which in turn indicates a decrease in the Si excess, as Fourier transform infrared spectroscopy (FTIR) reveals, so that, the film and junction composition changes with the growth temperature. The analysis of the photoluminescence (PL) results using the quantum confinement model suggests the presence of silicon nanocrystal (Si-nc) embedded in a SiOx matrix. For the case of the as-grown SiOx films, the absorption and emission properties are correlated with quantum effects in Si-nc and defects. For the case of the as-grown (SiOx/SiOy) junctions, only the emission mechanism related to some kinds of defects was considered, but silicon nanocrystal embedded in a SiOx matrix is present. After thermal annealing, a phase separation into Si and SiO2 occurs, as the FTIR spectra illustrates, which has repercussions in the absorption and emission properties of the films and junctions, as shown by the change in the A and B band positions on the PL spectra. These results lead to good possibilities for proposed novel applications in optoelectronic devices.