Luminescence properties of Si nanocrystals embedded in optical microcavities

Strong room temperature photoluminescence (PL) in the wavelength range 700–950 nm has been observed from Si nanocrystals (nc) obtained by high-temperature annealing of SiOx thin films prepared by plasma enhanced chemical vapor deposition (PECVD). A marked redshift of the luminescence peak has been detected by increasing the Si concentration of the SiOx films or the annealing temperature, due to the larger Si nc mean size obtained under these conditions. Narrower and more intense PL spectra are observed by decreasing the Si concentration of the SiOx samples or by increasing the annealing temperature, but the overall performances remain still far from those required for application of this material in optoelectronic devices. On the other hand, by embedding Si nc within Si/SiO2 Fabry–Pérot microcavities, extremely narrow (Δλ∼1.5 nm) and very intense PL peaks can be obtained. The emitted wavelength can be tuned within a wide range by properly varying the cavity resonance. The PL intensity is more than an order of magnitude above that of similar samples outside the cavity and the luminescence is strongly directional.