On the origin of the 417 and 437 nm double-peak emission in porous Si with crystallite sizes smaller than 3.0 nm

Abstract

Exploration of strong blue emission from Si nanostructures has been a subject of enormous experimental studies since the discovery of porous Si in 1990. It is revealed in this work that a strong blue double-peak (417 and 437 nm) photoluminescence (PL) can be obtained from fresh and thermally annealed porous Si with crystallite sizes smaller than 3.0 nm, when excited at the 370 nm line of a Xe lamp. The blue double-peak PL is stable in air and shows no crystallite size dependence. Its intensity varies with thermal annealing time, but its peak position remains unchanged. Spectral analyses suggest that the double-peak PL is closely related to the existence of small Si nanocrystallites, but cannot be explained by the quantum confinement effect. A theoretical calculation about electronic states caused by the vacancy defects in the gap of small Si balls is in good agreement with our experiments.