Study of Luminescent Silicon-Rich Silicon Nitride and Cerium and Terbium Doped Silicon Oxide Thin Films

Abstract

<p>Silicon nanostructures formed in silicon-rich silicon nitride (SRSN) and cerium and terbium doped silicon oxide thin films grown using different types of plasma-enhanced chemical vapour deposition have been studied through photoluminescence (PL) and synchrotron-based X-ray absorption spectroscopies to determine the effects of deposition and processing parameters on the luminescent and structural properties of these materials. The SRSN films exhibited bright PL attributed to quantum confinement effects in the silicon nanoclusters (Si-ncs) as well as radiative defects in the silicon nitride host matrix. The peak emission energy could be tuned from the near-infrared across the entire visible spectrum by controlling the film composition and the post-deposition annealing temperature and time to change the size of the Si-ncs. Preliminary experiments on cerium doped SRSN samples indicated that although the cerium ions coordinate in the optically active trivalent oxidation state, they were not effectively sensitized by Si-ncs in the films tested, most likely due to the nanoclusters having bandgap energies that were unsuitable for this purpose. In cerium and terbium co-doped silicon oxide films, cerium disilicate (Ce₂Si₂O₇) nanocrystallites were formed by annealing at temperatures of 900°C and higher. The A-Ce₂Si₂O₇, G-Ce₂Si₂O₇, and Ce₆[Si₄O₁₃][SiO₄]₂ phases of cerium disilicate were observed to form under different deposition and annealing conditions. All three phases exhibited extremely bright violet-blue PL and were found to efficiently sensitize green emission from co-dopant Tb³⁺ ions in the films. The Tb³⁺ luminescence predominantly corresponded to the ⁵D₄→⁷F_3–6 emission lines, although weak ⁵D₃→⁷F_2–6 emission lines were also observed in films containing relatively high concentrations of terbium indicating that the sensitization of Tb³⁺ ions occurred through the ⁵D₃, ⁵L₁₀, or ⁵D₂ energy levels.</p>