A comparative study of a-SiCxOyHz thin films grown via chemical vapor deposition for silicon photonics

We have previously demonstrated strong room-temperature luminescence at 1540 nm from erbium-doped amorphous silicon oxycarbide (a-SiCxOyHz:Er) materials. In this study, pertinent details are presented regarding the role of growth conditions and post-deposition thermal treatment in engineering the structural and optical characteristics of these novel Si-based materials for optimized luminescence performance. Three different classes of a-SiCxOyHz materials were synthesized by thermal chemical vapor deposition, as classified by their carbon and oxygen concentrations: SiC-like; Si-C-O; and SiO2-like. Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, nuclear reaction analysis, and spectroscopic ellipsometry were used to characterize the effects of thermal annealing, as performed at temperatures in the range of 500 - 1100°C, on the structural and optical properties of the resulting films. As the material evolves from the SiC-like, through the Si-C-O, to the SiO2-like matrix, the mass density and refractive index are found to decrease, whereas the optical band gap actually increases. Thermal annealing also resulted in hydrogen desorption from and densification of the a-SiCxOyHz films and in an accompanying decrease in optical gap and an increase in film refractive index. This work suggests that silicon oxycarbide could be a promising Si-based matrix for high-performance Er-doped waveguide amplifiers.