Light particle irradiation effects in Si nanocrystals

Si nanocrystals, formed by Si ion implantation into SiO2 layers and subsequ ent annealing at 1150 degrees C, were irradiated at room temperature either with He+ ions at energies of 30 or 130 keV, or with 400 keV electrons. Tra nsmission electron microscopy (TEM) and photoluminescence (PL) studies were performed. TEM experiments revealed that the Si nanocrystals were ultimate ly amorphized (for example at ion doses similar to 10(16) He cm(-2)) and co uld not be recrystallized by annealing up to 775 degrees C. This contrasts with previous results on bulk Si, in which electron- and very light ion-irr adiation never led to amorphization. Visible photoluminescence, usually asc ribed to quantum-size effects in the Si nanocrystals, was found to decrease and vanish after He+ ion doses as low as 3 x 10(12)-3 x 10(13) He cm(-2) ( which produce about 1 displacement per nanocrystal). This PL decrease is du e to defect-induced non-radiative recombination centers, possibly situated at the Si nanocrystal/SiO2 interface, and the pre-irradiation PL is restore d by a 600 degrees C anneal. (C) 1999 Published by Elsevier Science B.V. Al l rights reserved.