Photoluminescence studies have been performed on Si fine particles prepared by several different techniques. Orange light emission has been observed in oxidized fine Si particles prepared by gas evaporation. Spectral measurements have shown that the visible light emission has a broad peak at about 1.9 eV accompanied by a significant amount of higher-energy components. The shift in apparent optical band-gap observed in the study ( approximately 0.8 eV) from that of single-crystalline Si(1.1 eV) can be explained by the quantum size effect expected to be observed in Si particles with a radius of about 15 AA. Similar above-band-gap luminescence has been observed in hydrogen-terminated Si particles (prepared by evaporation in pure hydrogen) without oxidation, indicating that the emission indeed comes from Si particles and not from the oxide layer. According to transmission electron microscopic study of porous Si prepared under specific anodization conditions, ultra-fine Si particles or clusters are found in the texture of the porous layer. The dimension of the microstructure is of the order of 20 AA, which is small enough to explain the visible light emission from porous Si in terms of the quantum size effect.
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