Strained silicon for photonics applications

Silicon photonics is being considered as the future photonic platform, mainly for the reduction of photonic system costs and the increase of the number of functionalities on the same integrated chip by combining photonics and electronics. However, silicon is a centrosymmetric crystal, which inhibits Pockels effect: a second order nonlinear effect which allows for light modulation at speeds that are not limited by carriers and driven at very low power consumption. Nevertheless, this limitation can be overcome by straining the crystal lattice and breaking the crystal symmetry, which can be achieved by depositing a SiN high-stress overlayer. Over the last few years, much research has been done exploring Pockels effect in strained silicon. In this work, we present a general overview of the subject. Moreover, we experimentally demonstrate Pockels effect in silicon waveguides strained by a SiN overlayer deposited by PECVD, showing a second order nonlinear susceptibility as high as 336 pm/V. This is, for our knowledge, the highest reported value in the literature for such kind of structures, which proves to be a relevant step towards efficient optical modulation in strained silicon.