Optical nonlinearities and ultrafast absorption dynamics in structurally tunable a:SiNx thin films

• Published in: Optics and laser technology Vol. 185; p. 112589
• Main Authors: Kuriakose, Albin, Acharyya, Jitendra Nath, Adnan, Mohammad, Srivastava, Pankaj, Soma, Venugopal Rao, Vijaya Prakash, G.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2025
• Subjects: Amorphous silicon nitride; Carrier lifetimes; Excited state dynamics; Optical nonlinearities; Stoichiometry variation; Optical nonlinearities; Carrier lifetimes; Amorphous silicon nitride; Excited state dynamics; Stoichiometry variation
• ISSN: 0030-3992
• DOI: 10.1016/j.optlastec.2025.112589

[Display omitted] •Significant stoichiometric dependence on optical properties of a:SiNx thin films.•Enhanced third-order nonlinearity in Si-rich a:SiNx thin films.•Dependency of nonlinearities with bandgap and molecular polarizability.•Variation of ultrafast absorption dynamics with stoichiometry. Amorphous non-stoichiometric silicon nitride (a:SiNx) has a wide and diverse range of optical and structural characteristic features based on the stoichiometric variation of silicon/nitrogen content. Such unique features are widely utilized in photonic and optoelectronic coatings and device concepts. Here we provide a comprehensive study of various silicon rich a:SiNx thin films (R = [N]/[Si] from 0.22 to 1.16) from structural, linear and nonlinear optical properties and ultrafast absorption dynamics using diverse experimental approaches. While X-ray photoelectron spectroscopy provides a comprehensive understanding of Si/N chemical compositional variation, the linear optical studies confirm the stoichiometric dependency. Ultrafast pump–probe (transient absorption) spectroscopy was utilised to analyse the excited state dynamics, which shows a significant correlation with the optical bandgap variation due to the stoichiometric composition. The extensive study of femtosecond laser-based third-order nonlinear investigations with varied laser intensities and excitation wavelengths provide in-depth information related to nonlinear absorption and bandgap/ molecular polarisation dependency. The studies also witnessed a strong correlation of third-order nonlinearities with linear refractive index and optical bandgap. The significant structural dependent linear and nonlinear optical features and the understanding of excited state dynamics could be highly useful for many new ideas for photonic and optoelectronic novel device concepts.