Photonic Materials & Devices › Optical modulators

Optical modulators

Strained silicon devices

The centrosymmetry of the silicon lattice prevents the development of active photonic components due to the absence of second-order non-linearities in the material. Strained silicon technology has been proposed as a new disruptive approach for enabling ultra-fast modulation devices based on the Pockels effect by breaking this symmetry by means of a highly stressed cover layer deposited on top of the silicon waveguide structure.

To explore this technology, an optimized plasma-enhanced CVD process has been developed at the NTC facilities to achieve highly stressed silicon nitride films to act as a stressor for different devices. Therefore, films with tensile and compressive stress have been obtained with values as high as 400MPa and -2GPa and making possible to compare the impact of both stresses types for the first time. Films have been characterized using Raman spectroscopy, determining its intrinsic stress, and studying key parameters related to film quality like the atomic bond arrangements in each composition. Strained silicon devices have also been developed to investigate the possible contribution of Pockels effect and to analyze the role played by free carriers and interface traps in the electro-optical response.

Figure 1

Figure 1. (a) Sketch of the fabricated device, (b) simulated strain inside the silicon waveguide for a silicon nitride cover layer with an intrinsic stress of -2GPa and (c) experimental results of the effective index change for strained silicon structures.


[1] I. Olivares, T. Angelova, & P. Sanchis, “On the influence of interface charging dynamics and stressing conditions in strained silicon devices.” Scientific Reports, 2017, vol. 7, no 1, p. 7241

[2] I. Olivares, T. I. Angelova, A. M. Gutierrez and P. Sanchis, "Recent advances in strained silicon devices for enabling electro-optical functionalities." 2017 19th International Conference on Transparent Optical Networks (ICTON), Girona, 2017, pp. 1-4.