Optical properties of nanostructured silicon-rich silicon dioxide

We have conducted a study of the optical properties of sputtered silicon-rich silicon dioxide (SRO) thin films with specific application for the fabrication of erbium-doped waveguide amplifiers and lasers, polarization sensitive devices and devices to modify the polarization state of light. The SRO thin films were prepared through a reactive RF magnetron sputtering from a Si target in an 0 2/Ar gas mixture. The film stoichiometry was controlled by varying the power applied to the Si target or changing the percentage of 02 in the gas mixture. A deposition model is: presented which incorporates the physical and chemical aspects of the sputtering process to predict the film stoichiometry and deposition rate for variable deposition conditions. The as-deposited films are optically anisotropic with a positive birefringence (nTM > nTE) that increases with increasing silicon content for as-deposited films. The dependence of the birefringence on annealing temperature is also influenced by the silicon content. After annealing, samples with high silicon content (>45 at%) showed birefringence enhancement while samples with low silicon content (<45 at%) showed birefringence reduction. A birefringence of more than 3% can be generated in films with high silicon content (50 at% Si) annealed at 11000 C. We attribute the birefringence to the columnar film morphology achieved through our sputtering conditions. Er was incorporated through reactive co-sputtering from Er and Si targets in the same O2/Ar atmosphere in order to investigate the energy-transfer process between SRO and Er for low annealing temperatures. By studying the photoluminescence (PL) intensity of Er:SRO samples annealed in a wide range of temperatures, we demonstrated that the Er sensitization efficiency is maximized between 600'C and 700 C. Temperature-resolved PL spectroscopy on SRO and Er:SRO samples has demonstrated the presence of two different emission sensitizers for samples annealed at 6000 C and 1 100 0 C. This comparative study of temperature-resolved PL spectroscopy along with energy Filtered Transmission Electron Microscopy (EFTEM) has confirmed that the more efficient emission sensitization for samples annealed at 6000 C occurs through localized centers within the SRO matrix without the nucleation of Si nanocrystals. Er-doped SRO slab waveguides were fabricated to investigate optical gain and loss for samples annealed at low temperatures. Variable stripe length gain measurements show pump dependent waveguide loss saturation due to stimulated emission with a maximum modal gain of 3 ± 1.4 cm -' without the observation of carrier induced losses. Pump and probe measurements on ridge waveguides also confirms the presence of SRO sensitized signal enhancement for samples annealed at 6000C. Transmission loss measurements demonstrate a significant loss reduction of 1.5 cm' for samples annealed at 600'C compared to those annealed at 1000 0 C. These results suggest a possible route for the fabrication of compact, high-gain planar light sources and amplifiers with a low thermal budget for integration with standard Si CMOS processes. Thesis Advisor: Professor Lionel C. Kimerling Title: Thomas Lord Professor of Materials Science and Engineering Thesis Supervisor: Dr. John R. Haavisto Title: Principal Member of the Technical Staff, Charles Stark Draper Laboratory ACKNOWLEDGEMENTS This thesis was prepared at The Charles Stark Draper Laboratory, Inc., under Internal Research and Development Project # 18052 Flame Hydrolysis Deposition Process Development. Publication of this thesis does not constitute approval by Draper or the sponsoring agency of the findings or conclusions contained herein. It is published for the exchange and stimulation of ideas.