Improved near-infrared luminescence of Si-rich SiO₂ with buried Si nanocrystals grown by PECVD at optimized N₂O fluence

The optimized N₂O fluence for plasma enhanced chemical vapor deposition (PECVD) growing silicon-rich substoichiometric silicon oxide (SiO_x) with buried Si nanocrystals is demonstrated. Strong room-temperature photoluminescence (PL) at 550-870 nm has been observed in SiO_x thin films grown by PECVD with N₂O fluence varying from 105 to 130 seem. After annealing from 15 to 180 min, a 22-nm-redshift of the PL has been detected. The maximum PL intensity is observed for the 30-min annealed SiO_x growing at N₂O fluence at 120 seem. Larger N₂O fluence and longer annealing time causes a PL blueshift by 65 nm and 20 nm, respectively. Such a blueshift is attributed to shrinkage in the size of the Si nanocrystals under the participation of dissolved oxygen atoms from N₂O. The (220)-oriented Si nanocrystals with radius ranging from 4.4 to 5.0 nm are determined. The luminescent lifetimes lengthens from 20 μs to 52 μs as the nc-Si size extends from 4.0 to 4.2 nm. Optimal annealing times for SiO_x preparing at different N₂O fluences and an optimum N₂O fluence of 120 seem are reported. Serious oxidation effect at larger N₂O fluence condition is observed, providing smaller PL intensity at shorter wavelengths. In contrast, the larger size nc-Si will be precipitated when N₂O fluence becomes smaller, leading to a weaker PL at longer wavelength. These results provide the optimized growth condition for the Si-rich SiO₂ with buried Si nanocrystals.