Interface state-related linear and nonlinear optical properties of nanocrystalline Si/SiO2 multilayers

Nanocrystalline Si (nc-Si)/SiO2 multilayers with dot size of 2.5 nm were prepared and their microstructures were characterized by cross-sectional transmission electron microscopy and Raman spectroscopy. A broad photoluminescence band centered at 870 nm was observed which can be ascribed to the recombination of photo-excited carriers via luminescence centers at the interfacial region of nc-Si/SiO2. Meanwhile, the nonlinear optical response of the multilayers under excitation of two laser pulse durations had been investigated through Z-scan technique, the pumping lasers were picosecond (λ = 1.06 μm, tp = 25 ps) and femtosecond (λ = 800 nm, tp = 50 fs) lasers, respectively. Under picosecond laser pumping, the saturation absorption was observed while the reverse saturation absorption happened under the femtosecond excitation. The model based on the interface state-assisted process was proposed to explain the observed optical nonlinearities.