Size-Controlled Si Nanocrystals for Photonic and Electronic Applications

A new approach for the fabrication of ordered Si quantum dots fully compatible with normal Si technology is presented. The preparation of SiO/SiO2 superlattices represents a simple and efficient method for fabricating highly luminescent Si nanocrystals and allows independent control of size, size distribution, and density. The Si nanocrystals can be arranged to a specific depth and for a specific number of layers with a nanometer adjustment. The density of the Si nanocrystals is in the range of 1019/cm3. TEM and XRD investigations confirm control of the upper limit of the nanocrystal size to an average size of below 2.5 nm with a full width at half maximum of 0.6 nm. We report on TEM images showing early states of phase separation in SiO/SiO2 superlattices and combine these results with IR and PL investigations. Three different states of phase separation are distinguished and correlated to specific luminescence and infrared features. Photoluminescence experiments after crystallization show a size-dependent blue shift of the luminescence from 950 to 750 nm and a luminescence intensity comparable to porous Si. The nearly size-independent PL intensity observed in our SiO/SiO2 superlattices indicates the achievement of independent control of crystal size and number. In addition, PECVD preparation of amorphous SiO/SiO2 superlattices is reported which shows a similar size dependent luminescence after crystallization.