Linear and nonlinear optical properties of Si nanocrystals in SiO2 deposited by plasma-enhanced chemical-vapor deposition

Abstract

Linear and nonlinear optical properties of silicon suboxide SiO x films deposited by plasma-enhanced chemical-vapor deposition have been studied for different Si excesses up to 24 at. %. The layers have been fully characterized with respect to their atomic composition and the structure of the Si precipitates. Linear refractive index and extinction coefficient have been determined in the whole visible range, enabling to estimate the optical bandgap as a function of the Si nanocrystal size. Nonlinear optical properties have been evaluated by the z-scan technique for two different excitations: at 0.80 eV in the nanosecond regime and at 1.50 eV in the femtosecond regime. Under nanosecond excitation conditions, the nonlinear process is ruled by thermal effects, showing large values of both nonlinear refractive index ͑n 2 ϳ −10 −8 cm 2 / W͒ and nonlinear absorption coefficient ͑␤ ϳ 10 −6 cm/ W͒. Under femtosecond excitation conditions, a smaller nonlinear refractive index is found ͑n 2 ϳ 10 −12 cm 2 / W͒, typical of nonlinearities arising from electronic response. The contribution per nanocrystal to the electronic third-order nonlinear susceptibility increases as the size of the Si nanoparticles is reduced, due to the appearance of electronic transitions between discrete levels induced by quantum confinement.

Photothermally Activated Two-Photon Absorption in Ion-Implanted Silicon Quantum Dots in Silica Plates

“…Nonlinear optical effects are strongly dependent on shape and size of Si nanoparticles. Nevertheless, these results are in good agreement with previous investigations performed with silicon nanoparticles measured at different wavelengths [25].…”

Si-nanocrystal-based LEDs fabricated by ion implantation and plasma-enhanced chemical vapour deposition

“…The samples are referred by P for PECVD and I for ion-implanted. A clear definition of the Si excess can be found in reference [14]. Deposited layers were fabricated with silane (SiH 4 ) and nitrous oxide (N 2 O) as source gases, by keeping constant the N 2 O flow and adjusting the N 2 O/SiH 4 ratio to the required Si contents.…”

Nonlinear Group IV photonics based on silicon and germanium: from near-infrared to mid-infrared

“…Silicon nano-crystals in silicon dioxide and silicon nitride have also been investigated as a nonlinear material, exhibiting higher nonlinear indices than crystalline silicon by an order of magnitude or more [36][37][38][39][40][41]. The values of n 2 , β TPA , and nonlinear FOM are also highly variable, if silicon excess, annealing temperature and wavelength change.…”

“…Materials engineering further enhanced the nonlinearity, e.g., in amorphous silicon under certain deposition conditions [31][32][33][34][35] and in Si-rich silicon oxide (SRO) and nitride (SRN) based on the formation of silicon nano-crystals [36][37][38][39][40][41].…”