Luminescence of Silicon Nanocrystals and Porous Silicon

Abstract

Silicon nanocrystals have been made by a high temperature aerosol method. When passivated with 0.5-1 nm of oxide, the crystallites luminescence with ca. 5% quantum yield at room temperature, at visible wavelengths about 1 eV above the bulk silicon band gap. Spectroscopy shows that the nanocrystals behave as indirect gap semiconductors with phonon induced spectra. The quantum yield at room temperature is high, not because the nanocrystals are somewhat direct gap like, but because the fast radiationless processes which dominate carrier dynamics in bulk silicon are suppressed in nanocrystal silicon. The dynamics become molecule-like in nanocrystal silicon.