MICROSTRUCTURE AND PHOTOLUMINESCENCE OF NANOCRYSTALLINE SILICON THIN-FILMS

Nanometre-sized silicon crystallites were achieved using the crystalli zation 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 consis ts of a substrate induced process forming needle-like silicon crystall ites and a strain induced process forming nanocrystalline regions. The crystallized thin films show intense violet and blue photoluminescenc e at room temperature which exhibit separated peaks at energies rangin g from 2.5 eV to 3.5 eV and shows no intensity degradation. The lumine scence from such small crystallites is suggested to be due to an enhan cement effect on the oscillator strength of the confined levels in zer o-dimensional systems. The observations of the violet and blue light e missions from silicon crystallites should be very important for novel optoelectronic device applications of silicon-based materials.