The influence of irradiation and subsequent annealing on Si nanocrystals formed in SiO2 layers

Luminescent Si nanocrystals formed in SiO2 layers were irradiated with electrons and He+ ions with energies of 400 and 25-130 keV, respectively. The effects of irradiation and subsequent annealing at 600-1000 degrees C were studied by the methods of photoluminescence and electron microscopy. After irradiation with low doses (similar to 1 displacement per nanocrystal), it was found that photoluminescence of nanocrystals was quenched but the number of them increased simultaneously. After irradiation with high doses (similar to 10(3) displacements per nanocrystal), amorphization was observed, which is not characteristic of bulk Si. The observed phenomena are explained in terms of the generation of point defects and their trapping by Si-SiO2 interfaces. Photoluminescence of nanocrystals is recovered at annealing temperatures below 800 degrees C; however, an annealing temperature of about 1000 degrees C is required to crystallize the precipitates. An enhancement of photoluminescence observed after annealing is explained by the fact that the intensities of photoluminescence originated from initial nanocrystals and from nanocrystals formed as a result irradiation are summed. (C) 2000 MAIK "Nauka/Interperiodica".