Abstract
The optimized N <sub>2</sub> O fluence is demonstrated for plasma enhanced chemical vapor deposition (PECVD) of Si-rich substoichiometric silicon oxide (SiO <sub>x</sub> ) films with buried Si nanocrystals. Strong room-temperature photoluminescence (PL) at 550-870 nm has been observed in SiO <sub>x</sub> films grown by PECVD under a constant SiH <sub>4</sub> fluence of 20 seem with an N <sub>2</sub> O fluence varying from 105 seem to 130 seem. A 22-nm-redshift in the central PL wavelength has been detected after annealing from 15 min to 180 min. The maximum PL irradiance is observed from the SiO <sub>x</sub> film grown at the optimal N <sub>2</sub> O fluence of 120 seem after annealing for 30 minutes. Larger N <sub>2</sub> O fluence or longer annealing time leads to a PL band that is blue-shifted by 65 nm and 20 nm, respectively. Such a blue shift is attributed to shrinkage in the size of the Si nanocrystals with the participation of oxygen atoms from N <sub>2</sub> O incorporated within the SiO <sub>x</sub> matrix. The (220)-oriented Si nanocrystals exhibit radii ranging from 4.4 nm to 5.0 nm as determined by transmission electron microscopy (TEM). The luminescent lifetime lengthens to 52 (is as the nc-Si size increase to > 4 nm. Optimal annealing times for SiO <sub>x</sub> films prepared at different N <sub>2</sub> O fluences are also reported. A longer annealing process results in a stronger oxidation effect in SiO <sub>x</sub> films prepared at higher N <sub>2</sub> O fluences, yielding a lower PL irradiance at shorter wavelengths. In contrast, larger Si nanocrystals can be precipitated when the N <sub>2</sub> O fluence becomes lower; however, such a SiO <sub>x</sub> film usually exhibits weaker PL at longer wavelength due to a lower nc-Si density. These results indicate that a N <sub>2</sub> O/SiH <sub>4</sub> fluence ratio of 6:1 is the optimized PECVD growth condition for the Si-rich SiO <sub>2</sub> wherein dense Si nanocrystals are obtained after annealing. © 2005 Materials Research Society.