Visible luminescence in Si/SiO2 superlattices

Amorphous Si/SiO2 superlattices with periodicities from 2 to 5 nm have been grown on (100) Si wafers by several different techniques: molecular beam epitaxy, magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). With the first two methods little or no hydrogen was incorporated during growth and visible photoluminescence (PL) was obtained at wavelengths from 520 to 800 nm. The shift in the PL peak position with Si layer thickness is consistent with quantum confined emission. Annealing the sputtered superlattices at temperatures up to 1100 degrees C produced a very bright red PL that is similar in intensity to that found in porous Si. The PL was also considerably enhanced by deposition on aluminum-coated glass substrates. For large numbers of periods (e.g., 425) the pi, was strongly modulated in intensity owing to optical interference within the superlattice. Similar quantum-confined pi, was also observed in the PECVD grown superlattices, where the amorphous Si layers were heavily hydrogenated. The blue-red cathodoluminescence observed from sputtered superlattices is due primarily to defects in the SiO2 layers.