Fabrication of nanometer sized Si dot multilayers and their photoluminescence properties

Silicon nanometer sized dot multilayers have been prepared by repeating low-pressure chemical vapor deposition (LPCVD) for dot formation and thermal oxidation for dot isolation. The multilayers show efficient photoluminescence after annealing at 1000°C, which reduces Si dangling bond density measured by electron spin resonance (ESR). The measured luminescence peak energy shifts from 1.25 to 1.64 eV as the dot height decreases from 15 to <1 nm. The optical bandgap measured by photothermal deflection spectroscopy (PDS) has a blue shift from 2.0 to 2.7 eV when the dot height changes from 6 to <1 nm. The photoluminescence (PL) efficiency for both single-layered and multilayered dots increases by two orders of magnitude as the dot height decreases from 15 to 5 nm and becomes constant for dots smaller than 5 nm. These results indicate that the luminescence is not caused by the band-to-band transition, but caused by the recombination through radiative centers existing in the Si/SiO2 interface region.