Implantation energy effect on photoluminescence spectroscopy of Si nanocrystals locally fabricated by stencil-masked ultra-low-energy ion-beam-synthesis in silica

The present paper focuses on the effect of the implantation energy in the fabrication of pockets of silicon nanocrystals (Si-NCs) by stencil-masked ultra-low-energy ion-beam-synthesis (ULE-IBS). Si ion implantation was carried out into 10 nm SiO2 layers using energies ranging from 1 up to 3 keV and a fluence of 1 × 1016 Si+/cm2. After mask removal the samples are furnace annealed at 1050 °C for 30 min under N2 atmosphere. Control of Si-NCs characteristics was examined as a function of the stencil aperture size. Then, different patterns of Si-NCs pockets were synthesized such as squares and gratings of line arrays. Photoluminescence (PL) spectroscopy under a confocal microscope was employed to map the NCs pocket arrays. These PL images were found to perfectly mimic the mask geometry. A change in PL intensity and a blueshift of the PL energy peak were observed near the edge of the pockets. These local changes were attributed to both a smaller size and a higher density of Si-NCs in such areas, probably due to a local decrease of the implanted fluence. AFM measurements of the oxide swelling as a function of the elaboration conditions were combined to PL results to evaluate the real implanted fluence, which is lower than the nominal one. The implanted fluence was also found to decrease with decreasing aperture size, until a threshold for the absence of Si-NCs formation is reached in sub-micron patterns.