Wavelength-tunable blue photoluminescence of <2 nm Si nanocrystal synthesized by ultra-low-flow-density PECVD Original Research Article

Strong blue photoluminescence (PL) spectra from Si nanocrystals (Si-ncs) embedded in Si-rich SiOx grown by PECVD at ultra-low N2O flow density and N2O/SiH4 flow ratios are characterized. The N2O flow density is kept as low as 25 sccm to restrict oxygen desorption and to completely facilitate SiH4 decomposition, thus minimizing the oxygen adsorption and suppressing the hydrogen-passivation on dangling bonds at the Si-nc surface. In contrast to the as-grown SiOx, the blue-shifted PL of the annealed SiOx is attributed to the small-size Si-ncs rather than to oxygen vacancy defects. High-resolution transmission electron microscopy analysis reveals dense Si-ncs with diameters of 1.7 ± 0.2 nm in annealed SiOx, contributing to a minimum PL wavelength of 370 nm. X-ray photoelectron spectroscopy indicates a critical O/Si composition ratio of >1.44 for precipitating small Si-ncs with significant Si–Si binding energy peak at 99.0 eV. The weakened hydrogen-passivation effect for precisely manipulating the Si-nc size blue PL is confirmed by Fourier transform infrared spectroscopy.