Silicon-rich silicon nitride: tailoring material properties for photonic integrated circuits

Abstract

Silicon-rich silicon nitride is a promising hybrid material platform for use in photonic integratedcircuits. During the deposition process the silicon content of the bulk material can be altered, allowing the material properties of the new hybrid material to be tailored between those of silicon and silicon nitride. Customisation of the material platform between the advantages of high-index contrast systems and low-index contrast systems is therefore possible. Furthermore, the bandgap energy and nonlinear Kerr index are related to the refractive index. Hence, optimisation of these properties can be accomplished via the silicon content of the material platform. In this work a series of silicon-rich silicon nitride platforms with refractive indices from the stochiometic 1.97 to 2.95 at a wavelength of 1550 nm have been developed and their linear optical properties and bond structures analysed as the silicon content increases. Propagation losses were measured on waveguides fabricated from 500 nm thick films. Examination of the bandgap reveals a relationship between the bandgap energy and the refractive index, which agrees well with literature values for silicon and silicon nitride. Log-log plot analysis of this relationship is performed and an underlying cause of the change in optical properties is suggested. Furthermore, by dispersion engineering of waveguide geometry it proved possible to design waveguide samples capable of sustaining the nonlinear phenomenon of supercontinuum generation using the same waveguide dimensions. Using these samples, it was possible to confirm that increasing silicon content also increases the dispersion. Supercontinua were obtained using a 100 fs pulsed excitation, with a centre wavelength of 1560 nm. By optimising the waveguide geometry for each silicon-rich silicon nitride platform, larger supercontinua is anticipated to improve upon these measurements. These results are of particular importance when designing new chip-scale devices.