The effect of ion dose and annealing ambient on room temperature photoluminescence from Si nanocrystals in SiO₂

Photoluminescence from Si implanted silica is studied as a function of ion dose and annealing ambient. The photoluminescence emission intensity from samples as-implanted and after annealing at 1000°C in Ar is shown to exhibit a distinct maximum as a function of ion dose, increasing in intensity for doses up to a critical value and then decreasing at higher doses. The latter decrease is believed to result from the increasing probability of energy transfer between optically active and optically inactive crystallites as the crystallite concentration increases. A second stage anneal in forming gas (N₂/H₂) at 500°C increases the emission intensity and results in a red-shift of the emission peak. The increase in intensity is believed to result from H passivation of non-radiative defects. However, this effect is shown to be temporary, with the emission intensity returning to its pre-passivation value over a period of months. This is shown to be consistent with the diffusive loss of hydrogen from the sample. Interestingly, the red-shift is shown to be irreversible.