EFFECT OF THE GAS AMBIENT ON THE INTENSITY OF THE VISIBLE PHOTOLUMINESCENCE FROM SI MICROCRYSTALLITES IN A SIO2 MATRIX FORMED BY ION-IMPLANTATION

The intensity of the visible photoluminescence at room temperature fro m Si nanocrystallites formed in SiO2 by Si+ ion implantation and subse quent annealing has been enhanced by employing a second anneal step in a forming gas ambient. Two different wafers were used; one was implan ted with a dose of 2 x 10(17) Si+ cm(-2) at an energy of 200 keV and t he other was implanted at energies of 200 and 150 keV with doses of 1 X 10(17) Si+ cm(-2) at each energy. The implanted samples were first a nnealed at 1300 degrees C for 30 minutes in a nitrogen ambient and sub sequently annealed at 400 degrees C to 1000 degrees C for 60 to 240 mi nutes in forming gas, Samples from the two wafers had different peak p hotoluminescent wavelengths at about 750 and 620 nm, respectively, aft er tile first anneal. Both exhibited an enhancement of peak photolumin escent intensity after the second anneal. In another experiment, nitro gen was used instead of forming gas but the increase in intensity was not as large. These phenomena are explained by bond re-ordering and th e passivation of the dangling bonds by the introduction of hydrogen.