Microstructure of porous silicon (PS) was observed through high-resolution transmission electron microscope to study a relationship between the microstructure and a photoluminescence (PL) from PS. Three PS samples were made through anodization with different current densities. The samples had different PL spectra and were supposed to have different microstructures. Threadlike structures of Si and Si crystallites in the PS layer were observed in all the samples. The threadlike structure has the same density in all samples and has very little structural change, in spite of a significant change of PL spectra. The density of the Si crystallites varies for the samples and has a strong correlation with the PL intensity. No particular change of crystallites shape was observed. The size of the crystallites ranges from a few nanometers to a few tens of nanometers. Although no positive evidence to a quantum confinement is indicated, the Si crystallites are responsible for a light emission from PS.
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