Optical properties of a microcavity containing silicon nanocrystals

In this study, silicon nanocrystals (nc-Si) were used as emitting material in a Bragg mirror based microcavity. nc-Si are synthesized by laser pyrolysis of silane with sizes ranging between 1.5 and 7 nm and with an average full width at half maximum of 0.8 nm Prior to the fabrication of the microcavity, the nc-Si were studied separately in order to fully characterize their optical properties. This is required for the design of a good optical microcavity. By using spectroscopic ellipsometry from 240 to 700 nm, the average optical indices of the nanocrystals were determined. The wavelength dependence of the optical response of the nc-Si layers showed a good agreement with a Tauc–Lorentz dispersion model. Both nc-Si refractive index and extinction coefficient spectra differed significantly from those of bulk crystalline and amorphous silicon. Microcavities were made of a silicon nanocrystals layer embedded in a half wave silicon oxide layer and surrounded by two Bragg mirrors. The mirrors were made of three and four couples of half wave bilayers of silicon oxide and titanium oxide. The cavity peak was centered at 680 nm. From photoluminescence angular distribution spectra, the microcavity effects are demonstrated.