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

Luminescent Si nanocrystals formed in SiO2 layers were irradiated with elec trons and He+ ions with energies of 400 and 25-130 keV, respectively. The e ffects of irradiation and subsequent annealing at 600-1000 degrees C were s tudied by the methods of photoluminescence and electron microscopy. After i rradiation with low doses (similar to 1 displacement per nanocrystal), it w as found that photoluminescence of nanocrystals was quenched but the number of them increased simultaneously. After irradiation with high doses (simil ar to 10(3) displacements per nanocrystal), amorphization was observed, whi ch is not characteristic of bulk Si. The observed phenomena are explained i n terms of the generation of point defects and their trapping by Si-SiO2 in terfaces. Photoluminescence of nanocrystals is recovered at annealing tempe ratures below 800 degrees C; however, an annealing temperature of about 100 0 degrees C is required to crystallize the precipitates. An enhancement of photoluminescence observed after annealing is explained by the fact that th e intensities of photoluminescence originated from initial nanocrystals and from nanocrystals formed as a result irradiation are summed. (C) 2000 MAIK "Nauka/Interperiodica".