Size-dependent optical absorption of silicon nanocrystals embedded in SiO2/Si3N4 hybrid matrix

Optical constants of silicon quantum dots (Si QDs) in SiO2/Si3N4 hybrid matrix on quartz substrates have been determined in the wavelength range of 350–2500 nm. Forouhi–Bloomer (F-B) dispersion model is applied to describe the optical properties of silicon nanocrystals and the mismatch due to global fitting is fixed point by point. To extract the specific optical bandgap of silicon nanocrystal samples, Tauc-plots with γ = 1/2 and γ = 1/3 are used and discussed for the spectral range of 2 eV–3 eV. The effect of quantum dot size on the optical bandgap is explored. The results from both Tauc-plot and photoluminescence show the trend that the optical bandgap increases with decreasing quantum dot size, which agrees with the prediction of quantum confinement.

► Si QDs in Si3N4/SiO2 hybrid matrix are synthesized by sputtering.
► F-B dispersion model and Hishikawa's method are combined to get optical constants.
► Optical bandgap are extracted by Tauc's method and PL.
► Tauc's method with γ = 1/2 and 1/3 is discussed.
► We obtained that the optical bandgap increases with the decreasing of QD size.