Microstructure and photoluminescence of nanocrystalline silicon thin films

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Abstract
Nanometre-sized silicon crystallites were achieved using the crystallization of amorphous silicon thin films on silicon substrates by means of a thermal annealing process. Transmission electron microscopy and X-ray diffraction measurements indicate grain diameters from 3 nm to 10 nm, depending on the annealing conditions. The crystallization consists of a substrate induced process forming needle-like silicon crystallites and a strain induced process forming nanocrystalline regions. The crystallized thin films show intense violet and blue photoluminescence at room temperature which exhibit separated peaks at energies ranging from 2.5 eV to 3.5 eV and shows no intensity degradation. The luminescence from such small crystallites is suggested to be due to an enhancement effect on the oscillator strength of the confined levels in zero-dimensional systems. The observations of the violet and blue light emissions from silicon crystallites should be very important for novel optoelectronic device applications of silicon-based materials.