Size limit on the phosphorous doped silicon nanocrystals for dopant activation

We studied the photoluminescence spectra of silicon nanocrystals doped with and without phosphorus as a function of isothermal annealing time. Silicon nanocrystals were prepared by the implantation of 80keV Si+ into a 500nm SiO2 film to an areal density of 8×1016 at/cm2. Half of the samples were co-implanted with P+ at 80keV to 5×1015 at/cm2. The photoluminescence of the annealed samples were photo-excited at wavelength of 405nm. For short anneal times, when the nanocrystal size distribution has a relatively small mean diameter, formation in the presence of phosphorus yields an increase in the luminescence intensity and a blue shift in the emission peak compared with intrinsic nanocrystals. As the mean size increases with annealing time, this enhancement rapidly diminishes and the peak energy shifts to the red. Our results indicate the donor electron generation depends strongly on the nanocrystal size. We also found a critical limit above which it allows dopant activation.