Enriching Si quantum dots in a Si-rich SiN_x matrix for strong χ⁽³⁾ optical nonlinearity

To meet the demand of all-optical data processing applications, the SiN_x layer with enriching Si quantum dots (Si-QDs) for achieving strong optical nonlinearity is demonstrated with its χ⁽³⁾ coefficient enhanced by three orders of magnitude larger than that of stoichiometric Si₃N₄. With excessive Si concentration enriched from 16.3% to 23.4%, the dense Si-QDs apparently self-assemble in the SiN_x matrix with an average size of ∼0.95 nm and volume density of 5 × 10¹⁹ # cm⁻³. The Si-QD doped Si-rich SiN_x not only enlarges its third-order nonlinear absorption coefficient from 0.01 to 1.8 m GW⁻¹, but also increases its nonlinear refractive index from 5.7 × 10⁻¹³ to 9.2 × 10⁻¹² cm² W⁻¹ at a wavelength of 800 nm, as attributed to the localized excitons with decreased effective Bohr radius in quantum confined Si-QDs. Such a SiN_x:Si-QD material enables strong optical nonlinearity in compact nonlinear nanophotonic waveguide devices developed for future all-optical data processors.